Reproductive endocrinologic alterations in female asymptomatic obesity
Ricardo Azziz, M.D.
Department of Obstetrics and Gynecology, Division of Reproductive Biology and Endocrinology, The University of Alabama at Birmingham, Birmingham, Alabama
Obesity is the most prevalent nutritional disor- der of affluent nations and has a broad and signifi- cant impact on many endocrinologic parameters. In reproductive endocrinology and gynecology, ex- cess body fat has been significantly associated with ovulatory dysfunction, hyperandrogenemia and hormone-sensitive carcinomas. To assess the im- pact of obesity, independent of the associated dis- ease process, the alterations in androgen, estrogen, insulin/glucose, gonadotropin and prolactin ho- meostasis in otherwise asymptomatic overweight females will be discussed. The effect of weight re- duction will also be described.
DEFINITION AND MEASUREMENT OF OBESITY
Obesity is the excess of body fat, a definition that requires the measurement of adipose tissue. Over- weightness, alternatively, denotes a body weight higher than some reference weight. Excess body fat and overweightness do not necessarily correlate, this relationship being determined by variations in body build and muscle mass. Relative weight can be further defined as the deviation of body weight in relationship to an arbitrary standard.
Direct measurements of total body fat are ex- tremely difficult, usually requiring autopsy analy- sis. Indirect measurements include: (1) simple rules used to estimate body fat (Broca index, “Magic 36” rule, ruler test, “Mirror test,” etc.); (2) anthropometric measurements (height/weight re- lationships, body relationships, body surface mea- surements, skinfold thicknesses, body circumfer-
ences, and diameters, etc.); (3) measures of body density; and (4) dilutional techniques.1 Dilutional methods involve the injection of a known quantity of isotope or other substance that, after equilibra- tion, allows an estimation of total body water, cell mass potassium, or fat cell mass. Alternatively, the measurement of body density by subject submer- sion into water uses an assumed average density of fat and nonfat tissues for the estimation of total body fat.
Anthropometric measurements, although sig- nificantly less accurate than dilutional techniques or densitometry, have the highest clinical utility. Height, weight, skinfold thickness, and body or limb circumference and diameter have been corre- lated with body fat content. It appears that weight/ height2 (body mass index or BMI) can be of value, although in women weight/height may be a more appropriate index.1 The ponderal index (height in inches/\ weight in pounds) appears to be the least satisfactory assessment of body fat when compared with body density or skinfold thickness measure- ments, although it is still frequently used.1 Deter- minations of subcutaneous skinfold thickness are also clinically useful. Unfortunately, there are a number of problems with this technique, including the selection of an appropriate instrument, of a site(s) for measurement, and observer reproduc- ibility. There is no single skinfold measurement that is a reliable index of total body fat for both men and women, and usually a combination of sites must be measured. The utility of skinfold thickness as a predictor of body fat decreases with age, be- cause body fat deposition occurs in areas other
than the subcutaneous tissue in older subjects.1 The measurement of limb or body circumferences and diameters can give a reliable estimate of body fat. Steinkamp and colleagues2 reported that in white females aged 25 to 44 years, the measure- ment of waist, iliac crest, arm and thigh circumfer- ences had a >85% correlation coefficient with body fat as measured by 40K and 137Cs dilution tech- niques. They also noted that weight alone had an 87% coefficient of correlation with estimated body fat.
Standardized weight/height tables are com- monly used for screening and categorizing subjects into different weight subsets. Various standards are available in the literature, the most popular be- ing those of the Metropolitan Life Insurance Com- pany, either of 19593 or 1983.4 The body weights at which the least mortality occurs (ideal body weight [IBW]) are slightly higher in the 1983 tables. Un- fortunately, these IBWs are still well below the av- erage weight for United States residents for each sex/height category. The use of these tables has a number of drawbacks in clinical investigation. First, they are based on individuals who are seeking life insurance, which may not represent a true cross-section of the United States population or of the population to be studied. In addition, each sub- ject is measured wearing shoes and clothes, which may vary in weight and height. Notwithstanding the arbitrary nature of these standards, they pro- vide a reasonable method for clinically screening and categorizing large populations.
Prevalence of Obesity
The prevalence of obesity in a population en- tirely depends on its definition, because weight is a continuum. If a body weight of >20% IBW is used (per 1959 Metropolitan Life Insurance Company standards), 40%, 46%, and 45% of women aged 40 to 49, 50 to 59, and 60 to 69 years are obese, respec- tively.5 Alternatively, using the 95th percentile of BMI, 5% of men and 3.8% of women in the United States are obese.6 If obesity is arbitrarily defined as a BMI over 30 kg/m2, 12% of females in the United States are obese.7
Obesity can be further classified into mild, mod- erate, and severe.8 Mild obesity denotes individuals weighing between 20% and 40% above IBW, and comprise about 90.5% of obese persons. Individuals who are between 41% and 100% overweight dem- onstrate moderate obesity and constitute 9% of obese subjects. Severe obesity (>100% IBW) is ex-
tremely rare and afflicts approximately 0.5% of obese subjects.
Fatness correlates with a number of demo- graphic characteristics. Women have a greater per- centage of body fat even in the same relative weight category as men. This difference is noticeable in early childhood and becomes more marked after puberty.9 In a complex fashion, socioeconomic sta- tus is negatively correlated with obesity in the United States.1 Obesity is consistently more com- mon in white than in black males. Alternatively, black women show a higher prevalence of obesity at all ages than do white women.1
Types of Obesity
In addition to the absolute quantity of excess body fat, the cell type and regional distribution of fat must also be considered. There appears to be two forms of excessive fat tissue. The first occurs through adipocyte hypertrophy leading to an in- creased cell size. The second presents as a hyper- plasia of adipose tissue or an increase in the num- ber of adipocytes.1º It was originally proposed that fat cells proliferate only in early life, and their number cannot be subsequently reduced.11 The propensity for obesity is then determined in early life. Subsequently, other investigators noted that the weight of each individual fat cell increases until total body fat approximates 30 kg.12 Beyond this amount of fat tissue, very little increase in the size of individual adipocytes occurs, whereas the num- ber of fat cells increases in a linear fashion. Thus all obese individuals demonstrate adipocyte hyper- trophy unless ill or attempting to lose weight. Pa- tients with more severe obesity will also have an increased fat cell number or hyperplasia.1º Unfor- tunately, it appears that once the fat cell number has increased, it cannot be reduced by dieting. There appears to be a closer association between metabolic disturbances and adipocyte size than with fat tissue hyperplasia. This may not hold true in all instances, because an increase in peripheral aromatase activity is correlated with a rise in the number of adipocytes and adipose tissue stromal cells but not with greater cell size.
The topographical distribution of fat cells throughout the body is also correlated with meta- bolic alterations. Men have a preponderance of adi- pose tissue accumulation in the abdominal region. Alternatively, women demonstrate fat accumula- tion in the midgluteal and femoral regions. This difference may relate to androgenicity13 and to
variations in insulin action on femoral/gluteal ver- sus abdominal fat.14 With the same degree of rela- tive excess weight, men have higher levels of tri- glycerides, fasting glucose and insulin, and higher sums of glucose and insulin levels during an oral glucose tolerance test (GTT). Men also have higher blood pressures. A male risk profile was identified in women who had an increase in abdominal obe- sity as determined by waist/hip circumference ra- tios (WHR).12 Evans and associates13 correlated a male-type fat topography in premenopausal fe- males with androgenicity. Hence, the quantity of excess body fat, its distribution and cell type should be considered when attempting to determine the metabolic/endocrine alterations of obesity.
Obesity is rarely the result of endocrinologic dis- orders. Alternatively, obesity can lead to a number of disturbances in androgen, estrogen, binding globulin, insulin/glucose, gonadotropin, and pro- lactin homeostasis. It is possible that some or all of these physiological alterations play a role in the genesis of obesity-related oligo-ovulation and hor- mone-sensitive carcinomas. It has been postulated that the increased incidence of oligo-ovulation in overweight women is due to a derangement in their sex steroid metabolism, in particular, of androgens.
ANDROGEN METABOLISM IN OBESITY
Oligo-ovulation and Obesity
Bayer15 reported in 1939 that increased body weight and decreased sugar tolerance was associ- ated with menstrual disturbances. Rogers and Mitchell16 noted that of 100 patients with men- strual disorders, 43 were >20% overweight. In a control group of eumenorrheic women, the inci- dence of obesity was only 13%. The association of corpulence and ovulatory disturbances has been confirmed in subsequent reports.17,18
One of the principal causes of oligo-ovulation is the so-called polycystic ovarian syndrome (PCOS)19 or the hyperandrogenic chronic anovula- tory syndrome. This syndrome is a heterogeneous disorder characterized by enlarged ovaries contain- ing multiple small (<5 mm) atretic follicles, hyper- androgenemia and a luteinizing hormone/follicle- stimulating hormone (LH/FSH) ratio of >3, with oligo-ovulation and/or hirsutism. Goldzieher and Green20, reviewing various reports, noted that the incidence of obesity among patients with PCOS ranged from 16% to 49%. These investigators nev- ertheless felt that there was a higher prevalence of
obesity among women with this syndrome. Hartz and associates21 reported that oligo-ovulatory hir- sute women were ≥30 pounds (13.6 kg) heavier (13.6 kg) than women with no menstrual abnor- malities, after adjusting for height and age. In this study, the incidence of anovulatory cycles was 8.4% for women weighing >74% IBW as compared with 2.6% for women within 20% of their ideal weight. In addition, a longer duration of obesity was associ- ated with increased facial hair.
The relationship between excess body fat and ovulatory disturbances appears to be stronger for early-onset obesity. Hartz and associates21 noted that the incidence of teenage obesity was greater among nulligravida married women than for pre- viously pregnant married females. In this study, teenage obesity was also more frequent among women undergoing surgery for polycystic ovaries than those having ovarian surgery for other rea- sons. In another report, 96% of women with the on- set of obesity after menarche reported normal men- ses as compared with 69% of women with a pre- menarchal onset of excess weight.22 Alternatively, Combes et al.17 reported that juvenile-onset obesity was less likely to be associated with later menstrual disorders (31%) when compared with pubertal or adult-onset obesity (53% and 51%, respectively). The relationship of peripubertal obesity and oligo- ovulation has been stressed by other investiga- tors.23
It is clear that weight loss will reestablish normal menstrual cycles in some of these obese oligo-ovu- latory women. In the study by Mitchell and Rog- ers,24 there was no clear correlation between the amount of weight lost and the return of menses. In another study, 13 obese anovulatory women, expe- riencing a reduction in body weight of >15%, re- sumed regular menstrual function.25 Ten of these women (77%) became pregnant without additional therapy. These observations have been confirmed by others.26 It should be noted that dietary restric- tion and starvation, independent of weight loss, have a significant effect on many endocrinologic systems. Nevertheless, weight loss clearly has a sal- utary effect on ovulatory function.
Women with PCOS exhibit multiple small (<5 mm) immature follicles throughout the ovarian cortex. Although there appears to be an association between obesity and PCOS, the ovarian changes observed in women with morbid obesity did not ap- pear to be similar to the pathological findings in PCOS27 or those seen after long-term androgen treatment.28 These data suggest that although
| Steroidb | Premenopausal/follicular | Postmenopausal | ||||
|---|---|---|---|---|---|---|
| Ovary | Adrenal | Peripheral | Ovary | Adrenal | Peripheralc | |
| A | 30-50 | 50-70 | 15 (D) | 10-25 | 75-85 | 15 (D) |
| T | 25 | 20 | 55 (A) | 30 | 30 | 45 (A) |
| 5 (D) | 5 (D) | |||||
| DHT | 0 | 0 | 80 (A) | 0 | 0 | 80 (A) |
| 20 (T) | 20 (T) | |||||
| DHA | 25 | 50 | 25 (DS) | 25 | 50 | 25 (DS) |
| DHA-S | 0 | 70 | 30 (D) | 0 | 70 | 30 (D) |
| 45-diol | 10 | 60-70 | 30 (D) | 5 | 60-70 | 30 (D) |
ª Modified from Vermeulen, A.29
৳ For additional abbreviations see text.
Within parenthesis is precursor for peripheral conversion.
there is a relationship between obesity and anovu- lation, PCOS and obesity-related oligo-ovulation are not identical.
Obesity appears to be associated with a higher risk of androgenic ovulatory dysfunction. It is not clear whether eumenorrheic, nonhirsute women demonstrate similar, if less dramatic, reproduc- tive-endocrinologic abnormalities. The alterations in the metabolism and control of androgens in eu- menorrheic and/or asymptomatic female obesity will be discussed.
Normal Androgen Metabolism
Androgens are secreted by the adrenal cortex and ovaries. Steroids with weak androgenic proper- ties can also be peripherally converted to stronger androgens. The origins of the principal circulating plasma androgens in pre- and postmenopausal women are summarized in Table 1. Androstenedi- one (A) is the most important precursor of testos- terone (T) and dihydrotestosterone (DHT), while dehydro-3-epiandrosterone (DHA) accounts for only 5% and 13% of circulating T in normal women.29,30
The clearance of androgens is accomplished by hepatic extraction and peripheral metabolism, which are highly dependent on the unbound por- tion of circulating steroid. Approximately 10% of T and 50% of A are metabolized peripherally in women.29 Clearance of androgens by the hepatic/ splanchnic circulation involves mainly catabolism via 5-a- and 5-6-reductase. Androgen metabolites are further conjugated by the liver (95% glucuronic and 5% sulfuric), facilitating their urinary excre- tion (Fig. 1). Some 15% of androgen sulfates are excreted in bile, of which 80% are reabsorbed in the gut.29
Abbreviations of peripheral sources: A, androstenedione; D, dehydroepiandrosterone; DS, dehydroepiandrosterone sulfate; T, testosterone.
Peripheral metabolism of androgens occurs in the various target tissues including skin, muscle, brain, and adipose tissue.29,31 A-ring (aromatiza- tion), 17-6-hydroxysteroid dehydrogenization, 5-a and 5-6 A-ring reduction, and 3-a and 3-8 oxo-re- duction give rise to potent androgens such as dihy- drotestosterone (DHT), or to weaker metabolites such as 5-a-androstane-3-a, 17-6-diol (3-a-diol), androsterone, and etiocholanolone (Fig. 1). These are subsequently conjugated by the liver and ex- creted in the urine and bile.
Androgens and Age
Before considering androgen metabolism in obe- sity, the effect of subject age and menopausal sta- tus on the production of A, T, and the adrenal an- drogens DHA and DHA-sulfate (DHA-S) should be considered. T levels are minimally lower in women after natural menopause when compared with premenopausal females. The clearance rate of T does not appear to change with menopause.32
Fourteen percent of A is converted to T, account- ing for 50% of total T production. A decrease in A levels with age and menopause probably explains the small difference between pre- and postmeno- pausal T levels. It is clear that the ovary continues to produce a significant amount of T in the post- menopause.32
In normal postmenopausal women, plasma con- centrations of A are about one-half that observed in premenopausal females. There is no difference in the clearance rate of this steroid between pre- menopausal and postmenopausal women.32 Andro- stenedione levels continue to decrease slowly after menopause, possibly due to a diminishing ovarian secretion with age.33 A decreasing adrenal produc-
Cholesterol
CH3
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-OH
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2
3
Pregnenolone
O
OH
Hydroxypregnenolone
Dehydroepiandrosterone (DHEA)
HO
OH
5-Androstene-3 3,17 ß -diol (Androstenediol)
0
0
0
1
CH3
C-O
OH
-OH
3
O
2
Progesterone
5
5
0
Hydroxyprogesterone
Androstenedione
O
Testosterone
O
7
Estrone
Estradiol
7
6
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OH
OH
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5a -Androstane dione
5 B -androstanedione (Etiocholanedione)
H
17 B-hydroxy-5 B -androstane-3-one
H
H
Dihydrotestosterone (DHT)
8
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8
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5 B -androstane -3ª, 17₿ -diol
5 @ -androstane- -3B. 17 ß-diol
5 a-androstane -3a, 17ß-diol
5 B -androstane-
17-on0
17-on0
17-one
(epi Androsterone) (ANDROSTERONEb) (epi Etiocholanolone) (ETIOCHOLANOLONEb)
17-oxo Pathway
17 ß -hydroxy Pathway
Free forms, and sulfate or glucuronide esters: To urine or bile
tion of androgens may also account for the drop- ping plasma A levels.
Adrenal androgen production clearly decreases with age in premenopausal34 and postmenopausal35 women. An impaired secretion of 17-hydroxy- progesterone, 17-hydroxypregnenolone, DHA, and A has been observed in postmenopausal women af- ter acute adrenal stimulation.36 Serum DHA-S concentrations decrease linearly with age, begin- ning at about 20 years, independent of meno- pause.35,37 In determining the effect of obesity on androgen metabolism, the age and menopausal state of the subjects must be considered.
Androgen Plasma Concentrations in Obesity
In adults or adolescents with eumenorrheic obesity, plasma concentrations of androgens do not appear to be increased and may actually be decreased with respect to normal weight con-
trols.38-42 When six precursors of T were considered as a group, a significant decrease in plasma levels was observed in obese eumenorrheic women.39 Un- bound T may be mildly increased in eumenorrheic premenopausal obesity. Zhang et al.39 observed in obese premenopausal females, that plasma levels of free T were increased by 70%, whereas total T and A remained normal. This difference did not reach statistical significance. Other studies did not con- firm an increase in the free T levels in premeno- pausal42 or postmenopausal43 subjects. Alterna- tively, Evans et al.13 noted that IBW and WHR correlated inversely with sex hormone-binding globulin (SHBG) levels and directly with the pro- portion of free T (Fig. 2).
It would appear that circulating levels of plasma androgens do not vary significantly with weight, and in fact may be slightly lower in overweight sub- jects. Because of an obesity-related decrease in the
2.0
r =- 0.49
r =- 0.44
P <0.001
P < 0.001
1.6
SHBG (µg/dl)
1.2
0.8
0.4
0
5
r = 0.44
r = 0.48
p < 0.001
P <0.001
4
% Free Testosterone
3
2
1
0
0.6
0.7
0.8
0.9
1.0
1.1
80
120
160
200
240
WHR
%IBW
circulating levels of SHBG (see below), the per- centage of free T may be somewhat elevated. Free T may be higher in women with upper body obesity than in other overweight women.
Androgen Clearance in Obesity
Samojlik et al.38 reported a higher production rate (PR) and metabolic clearance rate (MCR) of T, DHT, and 3-a-diol in obese eumenorrheic women when compared with normal weight sub- jects. The MCR of T was 1,256 ± 145 L/day and 740 ± 40 liters/day in obese and normal-weight women, respectively. Because serum androgen lev- els were the same or slightly lower, the calculated production rates of T, DHT, and 3-a-diol were 1.5- to 3-fold higher in obese subjects. This obesity-re- lated increase in MCR and PR was also reported for androstenedione and DHA (Fig. 3).44 Both BMI and WHR correlate with the MCR of androstene- dione and DHA, and the PR of androstenedione. The PR of DHA did not appear to be associated with the WHR, suggesting that the production of A is more important for the development of upper- body obesity.
The etiology of the obesity-related increase in androgen MCR maintaining normal circulating levels is not clear. T and DHT are bound by SHBG in the circulation.45 This carrier protein has a high affinity for these steroids, but a low carrying capac- ity. As will be discussed below, the circulating lev- els of SHBG decrease with obesity by a mechanism yet to be understood. As SHBG levels decrease, the
5000
p < 0.001
p < 0.05
☐ Normal
MCR L/24 hr
4000
T
☒
Obese
I
3000
T
2000
T
1000
0
700
n.s.
n.s
600
500
IC ng/dl
400
300
200
100
0
20
p < 0.05
p < 0.01
PR mg/24 hr
15
10
T
5
0
A
DHEA
MCR of T increases probably by increasing the fraction of unbound T available for hepatic extrac- tion and clearance.46,47 Because A, DHA or DHA- S are not bound significantly by SHBG (Table 2), variations in the concentration of this carrier pro- tein with obesity does not explain their increased
| % Activity€ | |
|---|---|
| Steroids w/ binding activityb | |
| DHT | 240 |
| T | 100 |
| 45-diol | 83 |
| E2 | 28 |
| Steroids w/o binding activityb (<5%*) | |
| F | |
| Progesterone | |
| E3 | |
| E1 | |
| A | |
| Androsterone | |
| Etiocholanolone |
ª Modified from Kato and Horton. 48
b For abbreviations see text.
” Relative activity of steroids determined by the displacement of 3H-testosterone from SHBG.
| Tissue/serum ratio€ | |
|---|---|
| Steroidb | |
| F | 0.4±0.7 |
| DHA | 13.2 ± 4.4 |
| A | 7.7±3.4 |
| T | 7.0± 3.0 |
| E1 + E2 | 2.2 ± 1.5 |
| Progesterone | 6.3 ± 7.0 |
| 17-hydroxyprogesterone | 4.0 ± 2.5 |
ª Modified from Feher and Bodrogi.49
b For abbreviations see text.
Mean ± standard error.
MCR. The increased clearance of these and other androgens may reflect adipose tissue sequestration or metabolism.
Fat tissue is able to sequester various steroids in- cluding androgens, probably secondary to their lipid solubility. Most sex hormones appear to be preferentially concentrated within human adipo- cytes rather than in plasma (Table 3).49 Only corti- sol and DHA-S are not significantly stored in fat tissue. Because the volume of fat in obese subjects is much larger than their intravascular space and the tissue steroid concentration is 2- to 13-fold higher than in plasma, the steroid pool of severely obese subjects is far greater than that of normal- weight individuals.
In addition to serving as a reservoir, fat tissue can be the site of steroid metabolism. Androgens can be irreversibly aromatized to estrogens or con- verted to other androgens, a reversible process (Fig. 1).51 17-6-hydroxysteroid dehydrogenase ac- tivity, which leads to the interconversion of A and T, has been observed in vitro in adipose tissue,52-54 although other investigators have failed to demon- strate its presence.55 Perel and Killinger52 reported that the intraconversion of T and A was demon- strated in both adipocytes and tissue stroma, al- though no comparison of their activities was made. They observed that the conversion of A to T was greater than that of T to A at similar substrate con- centrations. Alternatively, Bleau et al.54 reported a conversion rate of 0.95% for A to T and 12.2% for T to A. These same researchers were unable to demonstrate aromatase activity in adipose tissue, which may suggest a problem with their particular experimental model. In vitro, both DHA and DHA- S were observed to inhibit 17-6-hydroxysteroid de- hydrogenase (as measured by the conversion of es- tradiol [E2] to estrone [E]].53 Aromatase activity in
adipose tissue (A to E] conversion) was not inhib- ited by adrenal androgens. This suggests that an increase in the adipose tissue concentration of DHA could alter androgen and estrogen intercon- version.
In vivo experiments suggest that adipose tissue contributes 5% to 10% of the overall conversion of A to T, but >2% of T to A.56 The level of unbound T correlates directly with the conversion of T to A.46 In spite of the in vitro data, there does not ap- pear to be a significant correlation between obesity and the conversion of T and A in vivo.57
The presence of 3-6-dehydrogenase activity in adipose tissue could lead to the conversion of DHA to A and 45-androstenediol (45-diol) to T. Horton and Tait30 observed that 6.5% of DHA was con- verted to A, while 0.7% was further metabolized to T in normal-weight women. They estimated that this conversion rate was in reasonable agreement with the hepatic metabolism of these steroids and concluded that no significant conversion of DHA to A or T occurred in peripheral tissues, includ- ing fat.
5-a-reductase activity was not observed in adi- pose tissue in vitro.55 The only significant activity these investigators noted in hamster adipose tissue. was 3-«-hydroxysteroid-oxido-reduction. This en- zymatic process encourages the formation of 3-a- diol from DHT (Fig. 1). They postulated that this enzymatic profile discourages the formation of DHT by adipose tissue and stimulates the forma- tion of the less androgenic T. In postmenopausal women, the level of unbound T correlated posi- tively with the conversion of T to DHT.46 Unfortu- nately, in this study, the association of 5-a-reduc- tase activity and body weight was not investigated.
Alterations in hepatic and urinary excretion may also influence the clearance of androgens. Feher and Halmy58 observed a deficient metabolism of DHA to DHA-S with a normal DHA-S to DHA conversion rate in obese women. The urinary ex- cretion of DHA was 10-fold higher in overweight subjects, whereas the excretion rate remained con- stant for DHA-S. These data suggested an obesity- related decrease in the sulfoconjugation of DHA or an increase in the desulfation of DHA-S. The in- creased urinary excretion of DHA may be second- ary to the higher glomerular filtration rate ob- served in obese women or to the intrinsic natri- uretic action of DHA.58 In addition, Samojlik et al.38 noted an increase in plasma and urinary levels of T and 3-a-diol glucuronide, with normal plasma concentrations of unconjugated steroids. These
data suggest that obesity is associated with an ac- celerated rate of hepatic conjugation and ex- traction maintaining normal androgen-circulating levels.
Between 1% and 5% of circulating A is converted to E1 in women. 47,51,57,59 Peripheral aromatization is responsible for a large fraction of androgen clear- ance and will be discussed further in the section on estrogen metabolism and obesity. In addition to aromatization, adipose tissue demonstrates a small degree of 17-ß-hydroxysteroid dehydrogenase ac- tivity, thus encouraging the conversion of A to T. Little other androgen metabolism occurs in adi- pose tissue. Adiposity also contributes to androgen clearance through steroid sequestration. Obesity- related alterations in hormone conjugation and ex- tractions may also play a role. Finally, the decrease in SHBG levels noted in obesity contributes to the increased MCR of T and other bound sex hor- mones.
Androgen Production in Obesity
It is possible that the obesity-related increase in androgen PR simply reflects a gonadal and adrenal compensation for the higher MCR observed, a ser- vocontrol mechanism.44 Alternatively, an increase in the ovarian or adrenal production of androgens may initially result in their higher circulating lev- els. The consequent decrease in the hepatic pro- duction and plasma concentration of SHBG leads to the increased MCR of bound steroids. In addi- tion, androgens may stimulate upper body fat de- position with a further increase in the steroidal MCR through adipose tissue sequestration and an- drogen metabolism.
There is no evidence that the ovarian enzymatic function is altered in euandrogenic obesity. An in- crease in the ovarian production of T and A may reflect the influence of other circulating factors al- tered in obesity, including insulin, gonadotropins, and prolactin. Alternatively, the obesity-related in- crease in the PR of A, DHA, and DHA-S may relate to alterations in adrenocortical function.
Adrenocortical Function in Obesity
Plasma cortisol (F), its circadian secretion, and the response of F to metyrapone or adrenocortico- tropic hormone (ACTH), are not altered in obe- sity.60-65 Normal plasma F levels are maintained in spite of an accelerated PR and MCR.62,66,67 A 30% to 50% increase in the urinary excretion of 17-hy- droxycorticosteroids is noted in obesity,61,62,67 but
this increase does not completely normalize when corrected for body surface area.62 It is felt that the increased MCR of F in obesity is secondary to a decrease in cortisol-binding globulin plasma con- centrations. Slavnov and associates68 have re- ported a slight increase in plasma ACTH levels in obese subjects, possibly explaining the increased F production. This obesity-related acceleration in the overall adrenocortical function may also lead to an increase in adrenal androgen production.
Urinary 17-ketosteroids (17-KS) measure vari- ous androgen metabolites including etiocholanol- one, androsterone, DHA, and epiandrosterone. Urinary 17-KSs have been reported to be elevated in obesity,69,70 although not all investigators agree.71 Hendrikx et al.72 observed that urinary an- drosterone and etiocholanolone were elevated in hirsute but were normal in nonhirsute, obese women. In addition, although anthropometric measurements correlated well with urinary gluco- corticoid levels, no significant correlation was noted for the 17-KS. This suggests that hyperan- drogenemia and not obesity is more closely related to the elevated levels of urinary adrenal androgen metabolites.
As previously noted, the circulating levels of DHA, A, and DHA-S are normal or slightly de- creased in obese subjects.13,40,44 In spite of this, an increased adrenal androgen PR and MCR have been reported. Feher and Halmy58 observed a higher PR of DHA and DHA-S in premenopausal obesity. In this study, an obesity-related increase in the MCR was observed for DHA-S, but not for DHA. Alternatively, Kurtz et al.44 reported that both the PR and MCR of DHA were elevated in obese women (Fig. 3). These authors noted a sig- nificant correlation between upper body obesity (WHR) and the MCR of DHA and A. Although the PR of A also was correlated to the WHR, the PR of DHA was not. This could suggest that an in- creased PR of A, but not of DHA, encouraged upper body fat deposition with its related aberrations in insulin/glucose homeostasis (see below).
Although the increased PR of adrenal androgens may occur solely in compensation for an increasing MCR, there appears to be alterations in adrenocor- tical dynamics in obese individuals. Brody and as- sociates reported a positive correlation between body weight and the change in DHA and the DHA/ 17-hydroxyprogesterone ratio after ACTH admin- istration, suggesting a hyperresponsiveness of adrenal androgens in obesity.73 The relative sen- sitivity and responsiveness of serum F, A, and
20
· Obese
15
· Normal
Cortisol ug/dl
4
10
5
0
800
A
600
DHEA ng/dl
400
200
0
100
75
4
A
ng/dl
50
25
0
0
30 60
120
240
ACTH ng/1.5m2/ hr
480
DHA to exogenous adrenocorticotropic hormone (ACTH) stimulation was studied in 16 obese eu- menorrheic premenopausal women.65 Using incre- mental doses of 1 to 24 ACTH, the relative respon- siveness of the steroids to ACTH was the same in obese and normal weight women: F > DHA > A (Fig. 4). The slope of the DHA response versus time was higher in obese women, indicating a greater “responsivity” to stimulation. Further- more, in obese women, the ACTH dose at which A began to rise was significantly lower (greater sensi- tivity) than in normal weight subjects. The sensi- tivity of the response of F or DHA to incremental doses of ACTH was not different in obese subjects. These investigators postulated an enhancement of ACTH-stimulated adrenal androgen production in asymptomatic obese women. Preliminary data in our laboratory have not confirmed any difference in the adrenal response to acute ACTH stimulation between eumenorrheic obese and normal weight premenopausal women.
Alterations in the adrenocortical production of adrenal androgens may reflect the influence of other factors, including adrenal androgens them- selves. Couch and associates74 reported significant
in vitro inhibition of human adrenocortical 17,20- desmolase activity by DHA, pregnenolone, and progesterone. 17-hydroxylase was inhibited to a much lesser degree. The increased adipose tissue sequestration and the higher urinary excretion of DHA could produce lower intra-adrenal concentra- tions of this steroid. This could lead to a reduced inhibition of adrenal 17,20-desmolase activity with a selective increase in the production of DHA and its metabolites.
Circulating estrogens may also influence adreno- cortical dynamics. As will be discussed below, the production of estrogens appears to increase with excess body fat. Lobo et al. reported that both oral conjugated estrogens75 and E2 pellets76 increased circulating adrenal androgen levels in postmeno- pausal women. An increase in the activity of adre- nal 3-ß-hydroxysteroid dehydrogenase and a de- crease in 17,20-desmolase function was observed in estrogen-treated women.75 In addition, obese women receiving E2 pellets had higher levels of A5- diol, A, and free T, and a higher androgen/estrogen ratio when compared with their nonobese counter- parts.76 Although other investigators have also doc- umented a rise in DHA and DHA-S concentrations after exogenous estrogen administration,77 most do not agree.78-79 Other researchers have also not ob- served an increase in 3-6-hydroxysteroid dehy- drogenase activity after exogeneous estrogen ad- ministration,80 and some have even reported an in- hibitory effect.81
In addition to adrenal androgens and estrogens, elevated testosterone with obesity may affect adre- nocortical function. A recent report by Vermesh et al.82 observed that the intravenous infusion of T re- sulted in a subtle inhibition of 21- and/or 11-hy- droxylase activity as measured by acute adrenal stimulation. They did not document any alter- ations in 17,20-desmolase or 3-6-hydroxysteroid dehydrogenase function. From this report, it ap- pears that short-term elevations in T levels do not produce an increase in the secretion of DHA and/ or DHA-S. It is not known whether chronic in- creases in circulating T have the same effect. Al- though the circadian rhythms of adrenal androgens and glucocorticoids correlate well,83 there are many circumstances in which their secretions diverge, i.e., trauma, suppressive therapy, adrenarche, and adrenopause.84- 84-86
Potentially, the factor(s) or mechanism(s) re- sponsible for the dissociation of cortisol and adre- nal androgen secretion could play a role in the ele- vated adrenal androgen production observed in
obesity. Prolactin (PRL) levels may also influence adrenal androgen secretion. Hyperprolactinemia has been associated with an elevation in serum DHA-S, reflecting primarily an increased DHA-S PR.87 The increased DHA-S production may be secondary to an elevated adrenal 17,20-desmolase activity, increased peripheral sulfokination, and/ or a decreased adrenal 3-6-hydroxysteroid hydrog- enase activity. Nonetheless, obesity does not ap- pear to be associated with elevated levels of circu- lating PRL (see below). Finally, insulin levels and insulin resistance are known to increase with ex- cess body fat (see below). Acute short-term hyper- insulinemia was associated with a slight decline in serum DHA-S levels,88 and a negative correlation was observed between DHA-S levels and insulin binding.89 These data suggest that obesity-related hyperinsulinemia may lead to a slight decrease in DHA-S levels, whereas elevated DHA-S levels may actually enhance insulin binding.
An increase in the PR of adrenal androgens can lead to the increased production of their metabo- lites. 45-diol, the 17-6-hydroxysteroid-dehydroge- nated metabolite of DHA, has unique estrogenic properties (Fig. 1). It is able to compete with the estrogen receptor, inhibits E2 metabolism, and in- creases the free fraction of E2 by displacing it from SHBG.84 Deslypere et al.53 noted a significant con- centration of 45-diol in abdominal and breast fat tissue. It is not known whether obesity is associ- ated with an increased production of 45-diol.
Weight Loss and Androgen Metabolism
If the alterations in androgen metabolism noted in obesity occur secondary to the excess body fat, a normalization should be expected after weight loss. Kopelman et al.90 observed increased serum levels of T and A and a decreased SHBG plasma concen- tration in massively obese women before weight loss. After jejunoileal bypass surgery, with an aver- age weight loss of 39.5 kg, a normalization in the levels of T, A, and SHBG was observed. Neither serum DHT nor F values varied with weight loss.90 Most reports have not observed a difference in the prediet total T levels and consequently do not re- port any change with weight loss.40,91,92 In these studies, the average weight loss ranged from 6.5 to 18 kg, somewhat less than was observed in Kopel- man’s study. Kim et al.92 reported a decrease in free T levels after weight reduction, which was depen- dent on the degree of weight loss. In their study, only women with an increase in ponderal index of
>0.5 demonstrated a significant decrease in free T and an increase in SHBG. Total T did not change.
Kopelman et al.90 noted a decrease in the plasma concentration of A after weight reduction. Alterna- tively, Grenman et al.40 observed an increase in A levels after an average weight loss of 13.2 kg. This study reported a lower initial A level in obese sub- jects than was in normal weight women. Other in- vestigators have also observed an increase in A lev- els with weight reduction.93 Pintor et al.,94 investi- gating peripubertal girls, reported a decrease in DHA levels after weight loss, whereas the plasma concentration of A decreased only in older prepu- bertal children. This report did not specify the de- gree of weight loss.
Starvation, independent of weight loss, may al- ter sex hormone levels. Acute fasting (7 to 10 days), with little weight loss, has a well-documented, det- rimental effect on adrenocortical function. Urinary and serum measurements of adrenal androgens and cortisol are noted to decrease acutely during the fasting period.95-97 Alternatively, O’Dea et al.91 studied obese postmenopausal women before, dur- ing, and after a supplemented fast and did not ob- serve a change in the total T level during these peri- ods. The metabolic alterations due to acute starva- tion independent of weight loss must be considered when interpreting steroid changes during weight reduction. Nevertheless, it appears that obesity-re- lated aberrations in the plasma concentration of androgens normalize after weight reduction in a linear fashion.
In summary, in eumenorrheic obesity, the PR and MCR of ovarian and adrenal androgens are in- creased, whereas serum levels are maintained nor- mal. The increased MCR may be due to an obesity- related decrease in the plasma concentration of SHBG. Steroid sequestration by fat may also in- crease steroid clearance, leading to an extremely large pool of sex hormones in obese individuals. Adipose tissue metabolism of steroids, including aromatization and 17-8-hydroxysteroid dehydro- genation, also contributes to the increased MCR of androgens, whereas alterations in hepatic conjuga- tion and extraction can also be a contributing fac- tor. The increased PR may simply be due to the operation of a servocontrol mechanism compensat- ing for the increased MCR. Alternatively, an aber- rant ovarian steroidogenesis may be present lead- ing to an elevated androgen production, although this remains to be demonstrated. In addition, changes in adrenocortical dynamics appear to fa- vor adrenal androgen secretion in obese eumenor-
rheic women. The increased ovarian and adrenal production and abnormal adrenal steroidogenesis noted in obesity may reflect changes in the intra- glandular and/or circulating concentration of an- drogens, estrogens, prolactin, insulin, and other unidentified factors. Notwithstanding the normal circulating concentrations of steroids in obesity, the accelerated turnover of androgens may in- crease the tissue exposure to these steroids, leading to a greater androgen effect. Although weight re- duction corrects any abnormality noted in steroid levels, it is not known whether the elevated PR and MCR of androgens also normalize after weight re- duction.
ESTROGEN METABOLISM IN OBESITY
Excess body fat leads to alterations in estrogen metabolism, which in turn may affect the hypotha- lamic-pituitary-ovarian axis leading to ovulatory dysfunction. Functional hyperestrogenism in obe- sity has also been associated with an increased risk of breast and endometrial carcinoma.
Obesity and the Development of Hormone- Sensitive Carcinoma
Wynder et al.98 reported that 48% of patients with endometrial carcinoma (Ca) were overweight, compared with 18% of the control population. The association between obesity and endometrial Ca has been stressed by others.99,100 The risk appears to increase linearly with the degree of excess weight and is 10-fold higher in subjects weighing 25 kg in excess of their IBW.101 The incidence of breast can- cer is also higher in obesity, being 48% greater for women weighing >80 kg than for those weighing less.102 This finding was significant only for women > 50 years of age. The risk of breast carcinoma ap- pears to be linearly correlated with the degree of excess weight.103 The mortality of breast malig- nancy and the risk of recurrence are also increased in overweight women. 104,10
Several mechanisms have been postulated to ac- count for the association between obesity and hor- mone-sensitive carcinomas. Overweight women may ingest greater quantities of lipid-soluble pre- carcinogens due to their preference for high-fat foods.106 Alternatively, exogenous carcinogens or precarcinogens may be lipid-soluble, leading to a greater accumulation in the adipose tissue in obese subjects, regardless of their particular dietary pref- erence.107 A change in the enteric flora of obese
women, with the production of endogenous carcin- ogens from biliary steroids may also occur.108 More prevalent is the hypothesis that stresses the associ- ation between the endocrinologic alterations of obesity, in particular estrogen metabolism, and cancer risk.
Estrogen Plasma Concentrations in Obesity
The production of estrogen and its precursors, including A and T, decreases with age and meno- pause.32 In reviewing estrogen metabolism in eu- menorrheic obesity, premenopausal and post- menopausal patients need to be examined sepa- rately. In premenopausal women, Trichopoulos et al.109 did not observe a difference in spot urinary E1 and E2 concentrations in women of different weights. Other investigators have also noted that the circulating serum levels of total E1 and E2 were no different between obese and normal weight pre- menopausal, eumenorrheic women42,110 or were slightly lower.40 In an attempt to eliminate the variability of single plasma measurements, the se- rum levels of E1 and E2 were assayed every 20 min- utes for 24 hours.39,111 No significant difference in the mean 24 hour concentration of E1 and E2 was observed in obese women. Eumenorrheic obese women demonstrate lower circulating SHBG lev- els13 (Fig. 2), suggesting that the free fraction of circulating E2 may be higher in obesity. Nonethe- less, Dunaif et al.42 were unable to confirm this.
In postmenopausal obese women, serum levels of E1 and E2 are mildly correlated with the degree of obesity and fat mass.112-115 Sex hormone-binding globulin concentrations are also lower in these older obese women, suggesting elevated E2 concen- trations. Investigating the role of free E2 in post- menopausal women with and without endometrial cancer, Davidson et al.116 noted that body size cor- related positively with total and free E2 plasma lev- els. E1- and E2-circulating concentrations progres- sively decrease with age in postmenopausal fe- males.112,113 The decrease in E1 and E2 serum levels begins 4 to 5 years earlier in obese women com- pared with normal weight controls.112 Thus chro- nologic age must be taken into consideration when comparing obese postmenopausal women with nor- mal weight controls. These data suggest that the circulating levels of E1 and total and/or free E2 are slightly higher in obese postmenopausal women. These increments are overshadowed in premeno- pausal women by the ovarian estrogen production, although free E2 may also be slightly elevated.
Peripheral Production of Estrogens in Obesity
West et al.117 first reported the aromatization of T to estrogens in castrated, adrenalectomized women. The aromatization of A to E1 by human adipose tissue has been demonstrated in vitro118,119 and in vivo in premenopausal51,59 and in postmeno- pausa157,120 women. Aromatase activity is detected primarily in the stroma of adipose tissue and not in intact adipocytes.121,122 Peripheral aromatization increases with age and is two- to fourfold higher in postmenopausal women.123 The efficiency of aro- matization increases secondary to a rise in the spe- cific activity of the aromatase enzyme in adipose stromal cells, independent of the greater levels of gonadotropins associated with menopause, but lin- early correlated with chronologic age.124,125 In two reports from the same laboratory, the average A- to-E1 conversion rate for premenopausal women was 1.5%59 compared with 3.9% in postmenopausal women.120
Androstenedione is the major substrate for pe- ripheral estrogen formation, 0.74% being aroma- tized.51 Only 0.15% of T is converted to E2, al- though this may be clinically significant, because this estrogen is much more potent than E1. Long- cope et al.57 reported a significant association be- tween body weight and the conversion of T to E2. DHA contributes very little to circulating estro- gens (0.05%) via its conversion to A.126
Although adipose tissue is a significant source of aromatase activity in women, Longcope et al.31 noted that muscle accounts for 25% to 30% of total peripheral aromatization and adipose tissue for 10% to 15% in men. The liver and other organs ac- count for the remaining portion of extragonadal aromatization. Nevertheless, the rate of peripheral A-to-E1 conversion is clearly correlated with body weight in premenopausal59 and postmenopausal women57,120,127 (Fig. 5). Because the majority of adi- pose tissue aromatase resides within the stromal compartment and most overweight patients do not have hyperplastic obesity, it is surprising to ob- serve such a consistent rise in A-to-E1 conversion with excess body fat. Either the quantity of adipose tissue stroma increases regardless of obesity cell type, or the activity of other sources of extragona- dal aromatization (e.g., hepatic) increases as well. This latter possibility is suggested by the data of Takaki et al.,128 who observed a rise in A-to-E1 con- version after significant weight loss. In addition, in vitro studies have suggested that the increase in A to E1 conversion observed in obesity occurs because
CONVERSION OF PLASMA ANDROSTENEDIONE TO ESTRONE
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of an increase in fat cell numbers and not to a change in the specific activity of the enzyme.124,125
The interconversion of E1 to E2 has been demon- strated in vivo129 and in vitro in adipose tissue.53 The conversion of E1 to E2 is approximately 5%, whereas 15% of E2 is converted back to E1 in pre- menopausal women.129 Adipose tissue 17-6-hy- droxysteroid dehydrogenase activity (measured by the conversion of E1 to E2) was higher in premeno- pausal than in postmenopausal women, and all fe- males had a greater activity than males.53 The con- version of E1 to E2 was also greater in omental than in subcutaneous abdominal fat, and was noncom- petitively inhibited by DHA and DHA-S. The sig- nificance of this finding is not clear, but it appears that circulating adrenal androgens may influence peripheral estrogen metabolism. Although estro- gen interconversion is observed in adipose tissue in vitro, Longcope et al.57 were not able to demon- strate an association between body fat and inter- conversion rates in vivo.
The metabolism of estrogens may also be altered in obesity. Normal estrogen metabolism begins with E2, which is subsequently oxidized to E1. E1 is metabolized to estriol (E3) via the 16-a-hydroxyla- tion pathway, or to catechol-estrogens via C2-hy- droxylation. Fischman et al.130 reported that obe- sity was associated with a significant decrease in C2-hydroxylation and an increased 16-a-hydroxyl- ation. A later report by the same laboratory con- firmed the obesity-related decrease in C2-hydroxyl- ation, although they were not able to demonstrate an alteration in the 16-a pathway.131 These meta-
bolic alterations can lead to a higher E3/catechol- estrogen ratio. Because E3 has significantly more estrogenic activity than 2-hydroxyestrone (a cate- chol-estrogen), the altered estrogen metabolism may contribute to the functional hyperestrogenism noted in obesity. Notwithstanding these metabolic disturbances, E3 probably contributes little to the overall estrogenic activity of normal premeno- pausal women regardless of weight.132
Estrogens are not a passive byproduct of obesity but can also promote adipose tissue proliferation. 17-6-estradiol, but not 17-a-estradiol, induced the replication and proliferation of adipocyte precur- sors in vitro. This growth stimulation was noted at physiological concentrations of estradiol.133
Weight Loss and Estrogen Metabolism
The effect of weight reduction on estrogen me- tabolism has not been clearly defined. DeWaard et al.134 reported that, after an average weight loss of 4.5 kg, urinary concentrations of E2 and E1 were slightly decreased in postmenopausal females. Ko- pelman and associates90 also observed a decrease in serum E2 levels after a 13.2-kg weight reduction in premenopausal women. E1 levels remained un- changed. Alternatively, other investigators have observed that after a 13- to 14-kg weight loss, se- rum E1 levels increased, whereas E2 remained the same in postmenopausal62 and premenopausal obese women.40 The effect of starvation, indepen- dent of weight reduction, must be considered. O’Dea and associates91 noted a significant decrease in serum E2 levels with fasting, although these val- ues returned to normal when the thinned subjects began refeeding.89 Surprisingly, Takaki et al.128 demonstrated an increase in the conversion of A to E1 in obese women losing an average of 45 kg. The stromal cells of adipose tissue are the major source of peripheral aromatase activity,122 so reduction in the size of the adipocytes should not significantly alter the stromal component or the A-to-E1 conver- sion rate. These authors suggested that starvation and weight loss may actually accentuate any obesi- ty-related increase in hepatic aromatization.
In summary, there is an increased production of estrogens, in particular E1, in obese women. The bulk of the increased estrogen PR is due to the aro- matization of circulating androgens by adipose-tis- sue stromal cells. The major substrate for periph- eral estrogen production is A through conversion to the weak estrogen E1. Testosterone contributes to a lesser degree via its conversion to E2, although
this activity probably is clinically significant due to the greater estrogenic activity of E2. Notwith- standing the increased peripheral aromatization noted in obesity, no consistent alteration in the plasma levels of E1 and E2 is observed in premeno- pausal women, due to the large quantity of ovarian estrogen secretion. Postmenopausal females dem- onstrate a slight increase in E1, E2, and free E2 plasma concentrations. Older subjects demon- strate a greater efficiency of peripheral aromatiza- tion and minimum ovarian secretion. Weight re- duction per se does not significantly change circu- lating levels of E2, whereas E1 levels and the conversion of A to E1 may actually increase.
SERUM BINDING OF SEX HORMONES IN OBESITY
Sex hormone-binding globulin (SHBG) is a cir- culating a-globulin produced by the liver, which binds in a high-affinity but low-capacity fashion, many of the circulating sex steroids. Some of these same steroids are also bound by albumin and by other less well-described carrier proteins.135 Sex hormone-binding globulin binds with varying affinity to the different steroids (Table 2).48
Traditionally, only the free fraction of sex hor- mone has been considered available for tissue ac- tion. More recently, the albumin-bound fraction of sex steroids also appears to be available for tissue interaction. Using a rat-brain perfusion model, Partridge et al.45 have demonstrated that albumin- bound steroid is readily transported into the brain substance, whereas antibody or SHBG-bound hor- mone is not. Tissue utilization of albumin-bound steroid depends on how closely the tissue-capillary transit time approximates the half-time of the hor- mone-protein dissociation rate. Tissues with high capillary transit time (e.g., liver, +5 seconds) will “strip” the steroid from albumin better than or- gans with short transit times (e.g., brain, +1 sec- ond). The percent of E2 not bound to SHBG or al- bumin is 2% to 3% in normal women, whereas un- bound T constitutes 1.5% to 2% of the total, as determined by in vitro experiments.136
Alterations in SHBG levels have a profound im- pact on the metabolism and action of bound ste- roids. A decrease in SHBG plasma concentration is associated with an increase in the MCR and free fraction of T46 and E2. 137,138 Furthermore, the blood conversion rates of T to A and T to DHT are posi- tively correlated with the free T fraction but are independent of total plasma T.46,139
The lower affinity of SHBG for E2 relative to T leads to an “estrogen amplification” effect with de- creasing SHBG plasma levels.45,136 Because of the high capillary transit time of the liver, free, albu- min-bound, and SHBG-bound E2 is available for hepatic metabolism and clearance. Due to its shorter capillary time, the brain only has free and albumin-bound E2 available for transport. Because SHBG has a fivefold greater affinity for T, only free and albumin-bound T are available for transport into the brain and liver. Thus with decreasing SHBG levels, the liver and other similar organs will experience a greater E2 effect relative to T. Subsequently, the E2/T clearance ratio decreases linearly with dropping SHBG levels. In conclusion, the differential affinity of SHBG for E2 versus T amplifies the effect of E2 on sensitive tissues, in particular, the liver.45
Sex hormone-binding globulin plasma concen- trations are influenced by a number of factors in- cluding estrogens, androgens, and obesity. It is known that the administration of estrogen leads to the increased hepatic production of various carrier proteins including cortisol-binding globulin, thyro- xine-binding globulin, ceruloplasmin, plasmino- gen, and transferrin. Alternatively, albumin, hap- toglobins, and total protein are decreased.139-142 The dosages of exogenous estrogens required to al- ter SHBG levels are usually large, achieving plasma levels similar to those observed during pregnancy.143 Lesser elevations, such as the endog- enous rise in E2 during the normal menstrual cycle, do not cause any significant change in SHBG levels. 143,144
Androgens decrease the circulating levels of SHBG and CBG,139,145 although they do not appear to alter the level of total proteins, albumin, hapto- globins, ceruloplasmins, or plasminogen. Thus the effect of androgens on the hepatic production of carrier proteins is not exactly opposite to that of estrogens. In addition, glucocorticoids may inhibit and thyroid hormones increase SHBG levels in normal subjects. 136
The mechanism by which estrogens and andro- gens affect the hepatic production and circulating levels of SHBG is not clear. Sex hormone-binding globulin levels appear to be relatively sensitive to the ratio of circulating androgen/estrogens throughout life. Before puberty there are no sexual differences in the levels of SHBG. At puberty, plasma SHBG concentrations decrease slightly in females and markedly in males,136 such decrease being attributed to the increased androgen produc-
tion noted at that time. Alternatively, Cunning- ham and associates146 studied men with untreated isolated gonadotropin deficiency and subjects with complete androgen insensitivity. They observed a decrease in SHBG levels during the second decade of life irrespective of androgen activity. These data suggest that the decrease in SHBG levels during the second decade of life is not entirely due to the increasing androgen levels. A fall in total T levels in men after 50 is associated with a slight increase in SHBG plasma concentrations, 136 although there does not appear to be any consistent change in the postmenopausal woman.
Obesity is clearly associated with lower SHBG levels in otherwise normal women (Fig. 2).39,40,110,147 Women who weighed >65 pounds (29.4 kg) above IBW had an SHBG capacity one-third that of indi- viduals within 5 pounds (2.26 kg) of IBW.147 Evans et al.13 also noted a linear correlation between SHBG plasma concentrations and WHR (Fig. 2), although other investigators have not confirmed this.40 A parallel reduction in binding capacity and SHBG concentration occurs in obese postmeno- pausal females. This indicates that the reduced plasma-binding capacity of SHBG in obesity is not due to impaired steroid binding but to a decrease in the number of circulating SHBG molecules.148
The mechanism by which obesity decreases the production of SHBG is not clear. As discussed above, obesity leads to a mildly hyperestrogenic state with greater E1 and possibly free E2 levels. As SHBG levels decrease, E2 should exert a greater effect on the liver than T (estrogen amplification effect). Although estrogens have been noted to in- crease the hepatic production of SHBG, this effect is observed only at supraphysiologic estradiol lev- els (e.g., with supraovulation) or with the oral ad- ministration of estrogens. Testosterone appears to exert a greater negative effect on the hepatic syn- thesis of SHBG than is E2 a positive influence. It is possible that obesity-related hyperandrogenemia (adrenal or ovarian) leads to an initial decrease in SHBG levels, a greater MCR of T and E2, and a new sex-hormone equilibrium.
Reed et al.149 have recently presented data corre- lating dietary lipid intake with plasma levels of SHBG. Six normal men consuming a high-fat diet for 2 weeks demonstrated an increase in mean plasma cholesterol levels and a decrease in SHBG level. Changing the diet to low-fat resulted in a sig- nificant reduction in plasma cholesterol and an in- crease in mean SHBG levels.149 The exact mecha- nism for dietary lipid-related SHBG decrease is not
clear. Overweight women consume a greater amount of fat in their diet than do normal weight individuals, and the decreased SHBG levels ob- served in obesity may be, in part, secondary to this dietary preference.
Most investigators90-93 report an increase in SHBG plasma concentrations after weight reduc- tion, and the extent of the rise in SHBG correlates linearly with the amount of weight loss.92 This in- crease is independent of whether exercise is part of the dietary plan. It appears that starvation has a synergistic effect with weight reduction in increas- ing SHBG levels.91 Women who were fasting and who had lost an average of 20 kg had higher SHBG levels than subjects who had lost an average of 25 kg but were not fasting.
In summary, obesity lowers the plasma concen- tration of SHBG by decreasing hepatic production through a mechanism yet to be elucidated. The drop in circulating SHBG leads to greater levels in the unbound fraction of free E2, T, and other sex steroids. In addition, secondary to the greater affinity of SHBG for T over E2, the influence of E2 on sensitive tissues is increased in obesity. As SHBG levels are reduced, the MCR for both E2 and T subsequently increases, and the conversion of T to DHT and T to A increases. Weight reduction serves to normalize the SHBG plasma concentra- tions.
INSULIN/GLUCOSE HOMEOSTASIS IN SIMPLE OBESITY
It is generally agreed that most obese women have an increased insulin resistance demonstrated by an elevated fasting serum insulin/glucose ratio, increased insulin levels after a GTT and an in- creased requirement for insulin during euglycemic clamp testing.150-153 Although fasting glucose plasma levels are similar in obese and nonobese women throughout the day, plasma insulin concen- trations are significantly higher in obese individu- als.154,155 The insulin resistance noted in most obese subjects appears to be secondary to a decrease in receptor number in the various tissues in- volved.152,156,157 In more severely obese individuals, postreceptor defects are also noted in vivo156 and in vitro.152 Although insulin is a potent antilipolytic hormone, free fatty acid levels are higher in obese hyperinsulinemic euglycemic individuals.154 This decreased ability of insulin to regulate free fatty acid levels was found to be independent of plasma glucagon or growth hormone concentrations. It ap-
pears that obese individuals have elevated levels of insulin and fatty acids in face of normal circulating plasma glucose and glucagon concentrations. These abnormalities in insulin/glucose homeosta- sis resolve on weight reduction.158-161
The relationship of insulin and androgens has received considerable attention in the study of pa- tients with PCOS. Nevertheless, insulin homeosta- sis in obese eumenorrheic subjects is not clear. Burghen et al. observed in six normal androgenic obese women a significant correlation between the basal levels of A and T, the basal levels of plasma insulin, and the insulin response to an oral GTT.162 Other investigators did not confirm these find- ings.42 Stuart et al.,163 using the euglycemic insulin clamp technique, observed that plasma A levels were augmented by the insulin infusion, whereas T concentrations did not change significantly. This alteration in plasma A levels was observed in both normal weight and obese women. Other investiga- tors88 have demonstrated in normal weight females that T levels remain unchanged during insulin in- fusion, whereas DHA-S concentrations actually decrease. A recent study by Schriock et al.89 ob- served a positive correlation between the insulin response curve levels after an oral GTT, and basal serum T, in normal weight women. Alternatively, a negative correlation between basal DHA-S and the insulin response was noted. These authors con- cluded that DHA-S may enhance insulin-binding action, whereas T has the opposite effect. In a study of 80 premenopausal women of various weights, no correlation between the various mea- sures of insulin activity and the plasma concentra- tions of T, A, DHA-S, or E2 was observed.13 Never- theless, this study reported that the percent of free T correlated directly with fasting plasma insulin levels and the insulin response to an oral GTT.
Female adiposity occurs predominately in the gluteal/femoral region possibly because of differ- ences in insulin binding and action between ab- dominal and femoral fat.14 Evans et al.13 and oth- ers12 have observed that an increase in upper body fat (higher WHR) was positively correlated with basal glucose and insulin levels and with the insu- lin response to an oral GTT. In addition, a high WHR also correlated with an elevated free T and with lower circulating SHBG levels (Fig. 2). Fur- thermore, there was a significant correlation be- tween the size of the adipocytes, the various mea- sures of androgenicity, and the insulin response to glucose loading.13 These data suggest that in- creased tissue exposure to unbound androgens may
lead to the localization of fat in the upper body, with enlargement of abdominal adipocytes, and the accompanying imbalance in glucose/insulin ho- meostasis. In a later study,164 these investigators reported that the decline in hepatic insulin extrac- tion and peripheral insulin sensitivity observed in obesity was partially mediated by an increased an- drogenic activity. In this study, the increase in pan- creatic insulin production noted with increasing weight was independent of androgenicity.164 Alter- natively, insulin receptors appear to be more nu- merous in the femoral fat of obese women, leading to an augmented glucose metabolism in this tis- sue.14 It is suggested that the higher insulin stimu- lation of glucose metabolism may promote the for- mation of a-glycerol phosphate within femoral fat cells and contribute to a more pronounced ability of femoral fat to synthesize and store acylglycerols. Hence, the distribution of fat in females (abdomi- nal vs. femoral) may hinge on the interaction of an- drogens and insulin.
In summary, obesity increases circulating levels of insulin by decreasing the number of the insulin receptors. Greater degrees of obesity may be also associated with postreceptor defects. These abnor- malities resolve with weight loss. There appears to be a positive correlation between insulin activity and the circulating level of androgens, in particular free T and A, in eumenorrheic women. This corre- lation is nevertheless weak and appears to be inde- pendent of weight. It is possible that a stronger cor- relation between androgens, insulin levels, and obesity is present if body fat topography is consid- ered. It is also possible that not all androgens have a detrimental influence on insulin activity, with DHA-S having a favorable effect.
GONADOTROPIN SECRETION IN OBESITY
Comparing premenopausal obese women with normal weight subjects of the same age, most inves- tigators have noted no difference in the basal or 24-hour luteinizing hormone (LH) and follicle- stimulating hormone (FSH) plasma concentra- tions,39,42,90 whereas some have observed a decrease in basal40 and 24-hour mean plasma concentra- tions.165 No significant difference in the LH pulsa- tility has been observed between normal weight and obese adolescent73 or premenopausal women.39 No abnormality in the LH and FSH response to the intravenous administration of gonadotropin- releasing hormone (GnRH)/thyrotropin-releasing hormone (TRH),110 or GnRH alone, 42 was observed
in eumenorrheic obese women. Follicle-stimulat- ing hormone- and LH-circulating levels are similar in obese and normal weight perimenopausal and postmenopausal women. Nevertheless, the peri- menopausal rise in FSH occurs 3 to 4 years earlier in overweight subjects.93,112
Weight reduction does not appear to have a great influence on premenopausal basal LH- and FSH- circulating levels.40,90,166 The response of gonado- tropins to GnRH was reported to be the same in obese subjects before and after weight reduction.165 Weight loss in postmenopausal females appears to increase FSH,91,93 with LH having a similar but less marked trend.91 The acute effect of starvation on serum and urinary gonadotropins in obese post- menopausal women was investigated, indicating that short-term fasting led to the excretion of large quantities of urinary gonadotropins.167 Notwith- standing, serum concentrations of LH and FSH did not change. The increased urinary concentration of gonadotropins was attributed to a starvation-re- lated inability of the renal proximal tubular cells to reabsorb and metabolize small proteins, including gonadotropins.
In general, eumenorrheic obesity does not ap- pear to be associated with gross alteration in go- nadotropin levels or their hypothalamic-pituitary control. Weight reduction may slightly increase FSH levels in obese postmenopausal women, al- though it has little effect on premenopausal circu- lating levels.
PROLACTIN IN EUMENORRHEIC OBESITY
Most reports note that the basal or 24-hour con- centration of PRL is normal in obese premeno- pausal and postmenopausal women,39,69,168-170 al- though a slight increase in the basal level of PRL was noted for obese prepubertal girls aged 7 to 9 years.64 No such difference was observed in over- weight girls aged 10 to 11 years. Weight reduction appears to have a limited effect on circulating PRL levels,40 although a slight decrease in the 24-hour concentration was observed after a 12-day fast.167 In spite of normal serum PRL values in obese sub- jects, the MCR and, subsequently, the PR of PRL correlate with body surface area.170
It is known that PRL levels have a nocturnal sleep-entrained peak. Copinschi and associates168 reported that the PRL peak was significantly de- layed in obese patients under basal conditions, oc- curring between 4:30 and 11:00 A.M. and after awakening in 4 to 5 subjects. This abnormality was
corrected by a 12-day fast (average weight loss of 8 kg). Alternatively, Kwa et al.172 noted that evening blood samples (5:30 to 8:30 P.M.) revealed higher PRL levels in nulliparous postmenopausal women weighing >70 kg than in their normal weight coun- terparts. This difference was not observed in par- ous postmenopausal women and was not confirmed by other studies of nocturnal hormonal profiles in obesity.173 In addition, neither the study by Kwa and associates172 nor Copinschi et al.168 specify the clinical characteristics of their patients. In eumen- orrheic premenopausal women, Zhang and associ- ates39 did not observe a difference in the 24-hour PRL pulse frequency or amplitude between obese and normal weight subjects.
Evidence has been presented supporting an ab- normality of PRL hypothalamic-pituitary control in obesity. The intravenous administration of TRH has been associated with a deficient rise in PRL in obese women.169,170 Impaired PRL release was also noted after insulin administration169,174 and arginine.174 Alternatively, Wilcox175 reported a normal PRL and TSH response to the administra- tion of TRH in obese premenopausal women. Al- though Cavagnini et al.174 also reported a normal PRL response to TRH in obese premenopausal subjects, the PRL rise after insulin and arginine infusion was impaired. Differences in PRL re- sponse to the administration of TRH could be at- tributed to the greater intravascular volume of obese subjects. Nevertheless, in obese women Donders et al.170 demonstrated a decreased PRL se- cretion after TRH infusion but an increased TSH response. These authors hypothesize that a central deficiency in serotonin may account for the dispar- ity in TSH and PRL responses to TRH in obesity.
Hyperprolactinemia has been associated with el- evations in the serum levels and the PR of DHA- S.87 Grenman et al.40 also noted a significant corre- lation between the WHR and PRL levels.40 In- creasing WHR is related to greater androgenicity. These data suggest that obesity-related androgeni- city, rather than obesity itself, is associated with subtle increases in serum PRL concentrations.
In summary, obese women do not appear to dem- onstrate any significant difference in baseline or 24-hour PRL concentrations. The circadian secre- tion of PRL and its hypothalamic control may be subtly impaired, although this remains to be con- firmed. Obesity-related abnormalities in PRL me- tabolism may be more closely associated with an- drogenicity than with excess body fat.
SUMMARY
Excess body fat has been clearly associated with an increased risk of oligo-ovulation and endome- trial/breast carcinoma. The connection has been assumed to lie within derangements of the meta- bolic/endocrine compartments, particularly of es- trogens and androgens. To differentiate the effect of obesity from its related disease process, an at- tempt has been made to define the reproductive- endocrinologic alterations encountered in other- wise asymptomatic obese women.
Androgen metabolism is accelerated in obesity. It is not clear whether the increased clearance pre- cedes or follows the accelerated production of an- drogens. A servocontrol mechanism appears to be operative in these asymptomatic individuals, maintaining plasma steroid levels normal. The un- bound fraction of T may be somewhat increased in overweight women with predominantly upper body fat deposition. The increased clearance of andro- gen may arise from an obesity-related depression in SHBG concentration (e.g., for T, E2, 45-diol, etc.). Adipose tissue, by virtue of the lipid solubility of most of these steroids, concentrates androgens, estrogens, and progesterone. This steroid seques- tration not only contributes to the obesity-related increase in androgen clearance but also leads to an extremely enlarged total body steroid pool. Fat tis- sue sequestration also increases the concentration of androgens in the vicinity of adipose stromal cells, possibly encouraging their aromatization. Adipose tissue also has a moderate degree of 17- hydroxysteroid dehydrogenase activity, which ap- pears to stimulate the conversion of A to T. Finally, alterations in peripheral and hepatic conjugation and an accelerated urinary excretion may contrib- ute to the elevated clearance of androgens.
The accelerated PR of androgens may simply re- sult as compensation for the elevated MCR in obe- sity. Nonetheless, evidence of alteration(s) in adre- nocortical steroidogenesis has been presented sug- gesting a selective obesity-related enhancement in adrenal androgen secretion. These remain to be confirmed. Nonetheless, adrenocortical abnormal- ities may arise secondary to the influence of other circulating and intra-adrenal factors, including in- sulin, prolactin, estrogens, and androgens. It is not known whether the accelerated androgen metabo- lism or the aberrant adrenal steroidogenesis im- prove with weight reduction.
Excess body fat increases androgen aromatiza- tion which, together with an obesity-related de-
crease in SHBG, is associated with mildly elevated levels of E1 and free E2 in postmenopausal women. Although premenopausal obese individuals have the same tendency, the far greater ovarian estrogen secretion overshadows any differences. The bulk of aromatization activity in fat lies in the stromal comportment. The major substrate for peripheral estrogen production is A. Testosterone also con- tributes to the estrogen pool via its conversion to E2. An increase in hepatic aromatization may also be present in obese individuals but remains to be clearly demonstrated. Weight reduction does not alter estrogen levels significantly, and the A-to-E1 conversion may actually increase.
Sex hormone-binding globulin plasma concen- trations and probably its hepatic production, are inversely correlated with body weight. The mecha- nism is not clear but may relate to the circulating androgen/estrogen ratio. The decreased SHBG levels are associated with higher free fractions of E2, T, 45-diol, and with an elevated MCR of bound steroids. The greater affinity of SHBG for T over E2 serves to amplify the effect of this estrogen on sensitive tissue. Sex hormone-binding globulin cir- culating levels normalize after weight loss.
Obesity is associated with insulin resistance sec- ondary to a decrease in receptor numbers, although postreceptor defects may also be present. In eu- menorrheic individuals, the correlation between obesity, insulin resistance, and hyperandrogene- mia is weak but appears to be stronger in women with upper body obesity. Individuals with a greater degree of upper body fat are also more susceptible to glucose/insulin and lipid abnormalities (male risk profile); although T levels may be positively associated with insulin resistance, DHA-S is prob- ably not. Abnormalities in insulin/glucose homeo- stasis return to normal after weight loss.
Gonadotropin secretion and control are not sig- nificantly different in obese women compared with normal weight subjects. Although abnormalities in the hypothalamic-pituitary control of PRL may be present in overweight individuals, circulating PRL levels remain normal. Accelerated MCR and PR of PRL are observed in obesity. In general, obesity leads to a hyperandrogenic/hyperestrogenic envi- ronment. Asymptomatic women are able to main- tain normal circulating plasma levels of steroids, although this does not preclude an increased expo- sure of sensitive tissues to the sex hormones. Obe- sity-related abnormalities in steroid metabolism and insulin/glucose, gonadotropin, and PRL ho- meostasis may play a role in their higher risk for
oligo-ovulation and/or hormone-sensitive carci- noma.
REFERENCES
1. Bray GA: The obese patient. In Major Problems in Inter- nal Medicine, Vol 9, Edited by LH Smith, Jr. Philadel- phia, WB Saunders Co., 1976, p 1
2. Steinkamp RC, Cohen NL, Gaffey WR, McKee YT, Bron G, Siri WE, Sargeant TW, Isaacs E: Measures of body fat and related factors in normal adults-II. J Chron Dis 18: 1291, 1965
3. New weight standards for men and women. Stat Bull Met- ropol Life Insur Co 40:1, 1959
4. 1983 Metropol height and weight tables. Stat Bull Metro- pol Life Insur Co 64:3, 1988
5. Frequency of overweight and underweight. Stat Bull Met- ropol Life Insur Co 41:4, 1960.
6. Health implications of obesity. Ann Intern Med 103:1073, 1985
7. Bray GA: Overweight is risking fate. In Human Obesity. Edited by RJ Wurtman, JJ Wurtman. New York, The New York Academy of Sciences, 1987, p 14
8. Stunkard AJ, Stinnett JL, Smoller JW: Psychological and social aspects of the surgical treatment of obesity. Am J Psychiatry 143:417, 1986
9. Weil WB Jr: The demographic characteristics of fatness and obesity. In Controversies in Obesity, Edited by BC Hansen. New York, Paeger Publisher, 1983, p 274
10. Sjostrom L: Fat cells and body weight. In Obesity, Edited by AJ Stunkard. Philadelphia, WB Saunders Co, 1980, p 72
11. Hirsch J, Knittle JL: Cellularity of obese and nonobese human adipose tissue. Fed Proc 29:1516, 1970
12. Krotkiewski M, Bjorntor P, Sjostrom L, Smith U: Impact of obesity on metabolism in men and women. J Clin Invest 72:1150, 1983
13. Evans DJ, Hoffmann RG, Kalkhoff RK, Kissebah AH: Relationship of androgenic activity to body weight topog- raphy, fat cell morphology, and metabolic aberrations in premenopausal women. J Clin Endocrinol Metab 57:304, 1983
14. Bolinder J, Engfeldt P, Ostoman J, Arner P: Site differ- ences in insulin receptor binding and insulin action in sub- cutaneous fat of obese females. J Clin Endocrinol Metab 57:455, 1983
15. Bayer LM: Build in relation to menstrual disorders and obesity. Endocrinology 24:260, 1939
16. Rogers J, Mitchell GW Jr: The relation of obesity to men- strual disturbances. N Engl J Med 247:53, 1952
17. Combes R, Altomare E, Tramoni M, Vague J: Obesity in menstrual disorders. In Medical Complications of Obesity, Serono Symposi, Vol 26, Edited by M Mancini, B Lewis, F Contaldo. New York, Academic Press, 1979, p 285
18. Nagata I, Kato K, Seki K, Furuya K: Ovulatory distur- bances. J Adolesc Health Care 7:1, 1986
19. Adamis J, Polson DW, Franks S: Prevalence of polycystic ovaries in women with anovulation and its idiopathic hir- sutism. Br Med J 293:355, 1986
20. Goldzieher JW, Green JA: The polycystic ovary. I. Clinical and histologic features. J Clin Endocrinol Metab 22:325, 1962
21. Hartz AJ, Barboriak PN, Wong A, Katayama KP, Rimm AA: The association of obesity with infertility and related menstrual abnormalities in women. Int J Obes 3:57, 1979
22. Friedman CI, Kim MH: Obesity and its effect on reproduc- tive function. Clin Obstet Gynecol 28:645, 1985
23. Yen SSC, Chaney C, Judd HL: Functional aberrations of the hypothalamic-pituitary system in polycystic ovary syndrome: a consideration of the pathogenesis. In The En- docrine Function of the Human Ovary, Edited by VHT James, M Serio, G Guisti. New York, Academic Press, 1976, p 373
24. Mitchell GW, Jr, Rogers J: The influence of weight reduc- tion on amenorrhea in obese women. N Engl J Med 249: 835, 1953
25. Bates GW, Whitworth NS: Effect of body weight reduc- tion on plasma androgens in obese, infertile women. Fertil Steril 38:406, 1982
26. Harlass FE, Plymate SR, Fariss BL, Belts RP: Weight loss is associated with correction of gonadotropin and sex ste- roid abnormalities in the obese anovulatory female. Fertil Steril 42:649, 1984
27. Fisher ER, Gregorio R, Stephan T, Nolan S, Danowski TS: Ovarian changes in women with morbid obesity. Ob- stet Gynecol 44:839, 1974
28. Amirikia H, Savoy-Moore RT, Sundareson AS, Moghissi KS: The effects of long-term androgen treatment on the ovary. Fertil Steril 45:202, 1986
29. Vermeulen A: Androgen secretion by adrenals and gonads. In Hirsutism and Virilism, Edited by VB Mahesh, RB Greenblatt. Boston, John Wright/PSG Inc, 1983, p 17
30. Horton R, Tait JF: In vivo conversion of dehydroisoan- drosterone to plasma androstenedione and testosterone in man. J Clin Endocrinol Metab 27:79, 1967
31. Longcope C, Pratt JH, Schneider SH, Fineberg SE: Aro- matization of androgens by muscle and adipose tissue in vivo. J Clin Endocrinol Metab 46:146, 1978
32. Judd HL: Hormonal dynamics associated with the meno- pause. Clin Obstet Gynecol 19:775, 1976
33. Purifoy FF, Koopmans LH, Tatum RW: Steroid hor- mones and aging: free testosterone, testosterone and an- drostenedione in normal females aged 20-87 years. Hum Biol 52:181, 1980
34. Musey VC, Collins DC, Musey PI, Martino-Saltzman D, Preedy JRK: Age-related changes in the female hormonal environment during reproductive life. Am J Obstet Gyne- col 157:312, 1987
35. Vermeulen A: Adrenal androgens and aging. In Adrenal Androgens. Edited by AR Genazzani, JHH Thijssen, PK Siiteri. New York, Raven Press, 1980, p 207
36. Vermeulen A, Deslypere JP, Schelfhout W, Verdonck L, Rubens R: Adrenocortical function in old age: response to acute adrenocorticotropin stimulation. J Clin Endocrinol Metab 54:187, 1982
37. Orentreich N, Brind JL, Rizer RL, Vogelman JH: Age changes and sex differences in serum dehydroepiandros- terone sulfate concentrations throughout adulthood. J Clin Endocrinol Metab 59:551, 1984
38. Samojlik E, Kirschner MA, Silber D, Schneider G, Ertel NH: Elevated production in metabolic clearance rates of androgens in morbidly obese women. J Clin Endocrinol Metab 59:949, 1984
39. Zhang Y-W, Stern B, Rebar RW: Endocrine comparison
of obese menstruating and amenorrheic women. J Clin Endocrinol Metab 58:1077, 1984
40. Grenman S, Ronnemaa T, Irjala K, Kaihola HL, Gronroos M: Sex steroid, gonadotropin, cortisol, and prolactin levels in healthy, massively obese women: correlation with ab- dominal fat cell size and effect of weight reduction. J Clin Endocrinol Metab 63:1257, 1986
41. Kaufman ED, Mosman J, Sutton M, Harris MV, Carmi- chael CW, Yen SSC: Characterization of basal estrogen and androgen levels and gonadotropin release patterns in the obese adolescent female. J Pediatr 98:990, 1981
42. Dunaif A, Mandeli J, Fluhr H, Dobrjanski A: The impact of obesity and chronic hyperinsulinemia on gonadotropin release and gonadal steroid secretion in the polycystic ovary syndrome. J Clin Endocrinol Metab 66:131, 1988
43. Brody S, Carlstrom K, Lagrelius A, Lunell NO, Moller- strom G, Pousette A: Serum sex hormone binding globulin (SHBG), testosterone/SHBG index, endometrial pathol- ogy and bone mineral density in postmenopausal women. Acta Obstet Gynecol Scand 66:357, 1987
44. Kurtz BR, Givens JR, Komindr S, Stevens MD, Karas JG, Bittle JB, Judge D, Kitabchi AE: Maintenance of normal circulating levels of 44-androstenedione and dehydroepi- androsterone in simple obesity despite increased meta- bolic clearance rates: evidence for a servo-controlled mechanism. J Clin Endocrinol Metab 64:1261, 1987
45. Pardridge WM: Transport of protein-bound hormones into tissues in vivo. Endocr Rev 2:103, 1981
46. Vermulen A, Ando S: Metabolic clearance rate and inter- conversion of androgens and the influence of the free an- drogen fraction. J Clin Endocrinol Metab 48:320, 1979
47. Rosenfield RL: Studies of the relation of plasma androgen levels to androgen action in women. J Steroid Biochem 6: 695,1975
48. Kato T, Horton R: Studies of testosterone binding globu- lin. J Clin Endocrinol Metab 28:1160, 1968
49. Feher T, Bodrogi L: A comparative study of steroid con- centrations in human adipose tissue and peripheral circu- lation. Clin Chim Acta 126:135, 1982
50. Mahesh VB: Personal communication.
51. Longcope C, Kato T, Horton R: Conversion of blood an- drogens to estrogens in normal adult men and women. J Clin Invest 48:2191, 1969
52. Perel E, Killinger DW: The interconversion and aromati- zation of androgens by human adipose tissue. J Steroid Biochem 10:623, 1979
53. Deslypere JP, Verdonck L, Vermuulen A: Fat tissue: A steroid reservoir and site of steroid metabolism. J Clin En- docrinol Metab 61:564, 1987
54. Bleau G, Roberts KD, Chapdelaine A: In vitro and in vivo uptake and metabolism of steroids in human adipose tis- sue. J Clin Endocrinol Metab 39:236, 1974
55. Blohm TR, Laughlin ME: Androgen metabolism in adi- pose tissue: conversion of 5-a-dihydrotestosterone to 3-a- androstenediol by hamster tissue. J Steroid Biochem 9: 603, 1978
56. Longcope C, Pratt JH, Schneider SH, Fineberg SE: The in vivo metabolism of estrogens by muscle and adipose tis- sue of normal men. Steroids 28:521, 1976
57. Longcope C, Baker R, Johnston CC Jr: Androgen and es- trogen metabolism: relationship to obesity. Metabolism 35:235, 1986
58. Feher T, Halmy L: Dehydroepiandrosterone and dehy-
droandrosterone sulfate dynamics in obesity. J Biochem 53:215, 1975
59. Edman CD, MacDonald TC: Effect of obesity on conver- sion of plasma androstenedione to estrone in ovulatory and anovulatory young women. J Obstet Gynecol 130:456, 1978
60. Kobberling J, Von zur Muhlen A: The circadian rhythm of free cortisol determined by urine sampling at two-hour intervals in normal subjects and in patients with severe obesity or Cushing’s syndrome. J Clin Endocrinol Metab 38:313, 1974
61. Scheingart DE, Gregerman RI, Conn JW: A comparison of the characteristics of increased adrenocortical function in obesity and in Cushing’s syndrome. Metabolism 12:484, 1963
62. Migeon CJ, Green OC, Eckert JP: Study of adrenocortical function in obesity. Metabolism 12:718, 1963
63. Laurian L, Herzberg M, Balas L: Metopirone test in over- weight subjects. Acta Endocrinol (Copenh) 51:261, 1966
64. Genazzani AR, Pintor C, Corda R: Plasma levels of gonad- otropins, prolactin, thyroxin, and adrenal and gonadal ste- roids in obese prepubertal girls. J Clin Endocrinol Metab 47:974, 1978
65. Komindr S, Kurtz BR, Stevens MD, Karas JG, Biddle JB, Givens GR: Relative sensitivity and responsivity of serum cortisol and to adrenal androgens to «-adrenocortico- tropin (1-24) in normal and obese, nonhirsute, eumenor- rheic women. J Clin Endocrinol Metab 63:860, 1986
66. Dunkelman SS, Fairhurst B, Plager J, Waterhouse C: Cor- tisol metabolism in obesity. J Clin Endocrinol Metab 24: 832, 1964
67. O’Connell M, Danforth E, Jr, Horton ES, Salans L, Sims EAH: Experimental obesity in men. III. Adrenocortical function. J Clin Endocrinol Metab 36:323, 1973
68. Slavnov VN, Epshtein EV: Somatotrophic, thyrotrophic, and adrenocorticotrophic functions of the anterior pitu- itary in obesity. Endocrinologie 15:213, 1977
69. Simkin V: Urinary 17-ketosteroid and 17-ketogenic ste- roid excretion in obese patients. N Engl J Med 264:974, 1961
70. Cigolini M, Micciolo R, Pelloso M, Vosello O: Urinary ex- cretion of androgens in obese women. In Medical Compli- cations of Obesity, Serono Symposia Vol 26, Edited by M Mancini, B. Lewis, F Contaldo. New York, Academic Press, 1979, p 289
71. Lobo RA, Paul WL, Goebelsmann U: Dehydroepiandros- terone sulfate as an indicator of adrenal androgen func- tion. Obstet Gynecol 57:69, 1981
72. Hendrikx A, Meulepas E, Heyns W, De Moor P: A com- parative study of the urinary excretion of glucocorticoids in 11-deoxy-17-ketosteroids in a group of obese women. Ann Endocrinol (Paris) 35:508, 1974
73. Brody S, Carlstrom K, Lagrelius A, Lunell N-O, Moller- strom G: Adrenal steroids in post-menopausal women: re- lation to obesity and bone mineral content. Maturitas 9: 25,1987
74. Couch RM, Muller J, Winter JSD: Regulation of the activ- ities of 17-hydroxylase and 17,20-desmolase in the human adrenal cortex: genetic analysis and inhibition by endoge- nous steroids. J Clin Endocrinol Metab 63:613, 1986
75. Lobo RA, Goebelsmann U, Brenner PF, Mishell DR, Jr: The effects of estrogen on adrenal androgens in oophorec- tomized women. Am J Obstet Gynecol 142:471, 1982
76. Lobo RA, March CM, Goebelsmann U, Mishell DR, Jr: The modulating role of obesity and 17-8-estradiol (E2) on bound and unbound E2 and adrenal androgens in oopho- rectomized women. J Clin Endocrinol Metab 54:320, 1982
77. Abraham GE, Maroulis GB: Effect of exogenous estrogen on serum pregnenolone, cortisol and androgens in post- menopausal women. Obstet Gynecol 45:271, 1975
78. Rose DP, Fern M, Liskowski L, Milbrath JR: Effect of treatment with estrogen conjugates on endogenous plasma steroids. Obstet Gynecol 49:80, 1977
79. Lucky AW, Marynick SP, Rebar RW, Cutler GB, Glen M, Johnsonbaugh RE, Loriaux DL: Replacement oral ethi- nyloestradiol therapy for gonadal dysgenesis: growth in adrenal androgen studies. Acta Endocrinol (Copenh) 91: 519, 1979
80. Anderson DC, Yen SSC: Effects of estrogens on adrenal 3-ß-hydroxysteroid dehydrogenase in oophorectomized women. J Clin Endocrinol Metab 43:561, 1976
81. Sobrinho LG, Kase NG, Grunt JA: Changes in adrenocor- tical function of patients with gonadal dysgenesis after treatment with estrogen. J Clin Endocrinol Metab 33:110, 1971
82. Vermesh M, Silva PD, Rosen GF, Vijod AG, Lobo RA: Effect of androgen on adrenosteroidogenesis in normal women. J Clin Endocrinol Metab 66:128, 1988
83. Huq MS, Pfaff M, Jespersen D, Zucker IR, Kirschner MA: Concurrence of aldosterone, androgen, and cortisol secre- tion in adrenal venous effluents. J Clin Endocrinol Metab 42:230, 1976
84. Adams JB: Control of secretion and the function of C19- 45-steroids of the human adrenal gland. Mol Cell Endocri- nol 41:1, 1985
85. Parker CR, Jr, Baxter CR: Divergence in adrenal steroid secretory pattern after thermal injury in adult patients. J Trauma 25:508, 1985
86. Avgerinos PC, Cutlers GB Jr, Tsokos GC, Gold PW, Feu- illan P, Gallucci WT, Pillemer SR, Loriaux DL, Chrousos GP: Dissociation between cortisol and adrenal androgen secretion in patients receiving alternate day prednisone therapy. J Clin Endocrinol Metab 65:24, 1987
87. Schiebinger RJ, Chrousos GP, Cutler GB, Jr, Loriaux DL: The effect of serum prolactin on plasma adrenal andro- gens and the production and metabolic clearance rate of dehydroepiandrosterone sulfate in normal and hyperpro- lactinemic subjects. J Clin Endocrinol Metab 62:202, 1986
88. Nestler JE, Clore JN, Strauss JF III, Blackard WG: The effects of hyperinsulinemia on serum testosterone, proges- terone, dehydroepiandrosterone sulfate, and cortisol lev- els in normal women and in a women with hyperandrogen- ism, insulin resistance, and acanthosis nigricans. J Clin Endocrinol Metab 64:180, 1987
89. Schriock ED, Buffington CK, Hubert GD, Kurtz BR, Ki- tabachi AE, Buster JE, Givens JR: Divergent correlations of circulating dehydroepiandrosterone sulfate and testos- terone with insulin levels and insulin receptor binding. J Clin Endocrinol Metab 66:1329, 1988
90. Kopelman PG, White N, Pilkington TRE, Jeffcoate SL: The effect of weight loss on steroid secretion and binding in massively obese women. Clin Endocrinol (Oxf) 14:113, 1981
91. O’Dea JPK, Wieland RG, Hallberg MC, Llerena LA, Zorn EM, Gunuth SM: Effect of dietary weight loss on sex ste-
roid binding, sex steroids, and gonadotropins in obese postmenopausal women. J Lab Clin Med 93:1004, 1979
92. Kim MH, Friedman CI, Barrows H, Rosenfield RL: Serum androgen concentrations in the massively obese reproduc- tive women: the response to weight loss. Trans Am Gyne- col Obstet Soc 1:26, 1982
93. Klinga K, von Holst TH, Runnebaum B: Serum concen- trations of FSH, oestradiol, oestrone, and androstenedi- one in normal and obese women. Maturitas 4:9, 1982
94. Pintor C, Genazzani AR, Buggioni R, Carboni G, Faedda A, Pisano E, Orani S, Fanni T, D’Ambrogio G, Corda R: Effect of weight loss on adrenal androgen plasma levels in obese prepubertal girls. In Adrenal Androgens, Edited by AR Genazzani, JHH Thijssen, PK Siiteri. New York, Ra- ven Press, 1980, p 59
95. Van Riet HG, Schwarz F, Der Kinderen PJ: Metabolic ob- servations during the treatment of obese patients by peri- ods of total starvation. Metabolism 13:291, 1964
96. Schultz AL, Kerlow A, Ulstrom RA: Effect of starvation on adrenal cortical function in obese subjects. J Clin En- docrinol Metab 24:1253, 1964
97. Hendrikx A, Heyns W, de Moor P: Influence of a low-calo- rie diet fasting on the metabolism of dehydroepiandroster- one sulfate in adult obese subjects. J Clin Endocrinol Metab 28:1525, 1968
98. Wynder EL, Escher GC, Mantel N: Epidemiological in- vestigation of cancer of the endometrium. Cancer 19:489, 1966
99. Damon A: Host factors in cancer of the breast and uterine cervix and corpus. J Natl Cancer Inst 24:43, 1960
100. MacMahon B: Risk factors for endometrial cancer. Gyne- col Oncol 2:122, 1974
101. Elwood JM, Cole P, Rothman KJ, Kaplin SD: Epidemiol- ogy of endometrial cancer. J Natl Cancer Inst 59:1055, 1977
102. Staszewski J: Breast cancer and body build. Prev Med 6: 410, 1977
103. Paffenbarger RS Jr, Kampert JB, Chang H-G: Character- istics that predict risk of breast cancer before and after the menopause. Am J Epidemol 112:258, 1980
104. Donegan WL, Hartz AJ, Rimm AA: The association of body weight with recurring cancer of the breast. Cancer 41:1590, 1978
105. Tartter PI, Papatestas AE, Ioannovich J, Mulvihill MN, Lesnick G, Aufses AH, Jr: Cholesterol and obesity as prog- nostic factors in breast cancer. Cancer 47:2222, 1981
106. Miller AV, Kelly A, Choi NW, Matthews V, Morgan RW, Munan L, Burch JD, Feather J, Howe GR, Jain M: A study of diet and breast cancer. Am J Epidemol 107:499, 1978
107. Beer AE, Billingham RE: Adipose tissue, a neglected fac- tor in etiology of breast cancer? Lancet 2:296, 1978
108. Hill MJ, Goddard P, Williams REO: Gut bacteria and eti- ology of cancer of the breast. Lancet 2:472, 1971
109. Trichopoulos D, Polychronopoulou A, Brown J, MacMa- hon B: Obesity, serum cholesterol, and estrogens in pre- menopausal women. Oncology 40:227, 1983
110. Kopelman PG, Pinlkington TRE, White N, Jeffocate SL: Abnormal sex steroid secretion in binding in massively obese women. Clin Endocrinol 12:363, 1980
111. Zumoff B, Strain GW, Kream J, O’Connor J, Levin J, Fu- kushima DK: Obese young men have elevated plasma es-
trogen levels but obese premenopausal women do not. Me- tabolism 30:1011, 1981
112. Klinga K, von Holst T, Runnebaum B: Influence of severe obesity on peripheral hormone concentrations in pre- and postmenopausal women. Eur J Obstet Gynecol Reprod Biol 15:103, 1983
113. Vermeulen A: Sex hormone status of the postmenopausal woman. Maturitas 1:81, 1980
114. Meldrum DR, Davidson BJ, Tataryn IV, Judd HL: Changes in circulating steroids with aging in postmeno- pausal women. Obstet Gynecol 57:624, 1981
115. Vermulen A, Verdonck L: Sex hormone concentrations in post-menopausal women. Clin Endocrinol 9:59, 1978
116. Davidson BJ, Gambone JC, Lagasse LV, Castaldo TW, Hammond GL, Siiteri PK, Judd HL: Free estradiol in postmenopausal women with and without endometrial cancer. J Clin Endocrinol Metab 52:404, 1981
117. West CD, Damast BL, Sarro SD, Pearson OH: Conversion of testosterone to estrogens in castrated, adrenalecto- mized human females. J Biol Chem 218:409, 1956
118. Schinder AE, Ebert A, Friedrich E: Conversion of andro- stenedione to estrone by human fat tissue. J Clin Endocri- nol Metab 35:627, 1972
119. Nimrod A, Ryan KJ: Aromatization of androgens by hu- man abdominal and breast fatty tissue. J Clin Endocrinol Metab 40:367, 1975
120. Macdonald PC, Edman CD, Hemsell DL, Porter JC, Siit- eri PK: Effect of obesity on conversion of plasma andro- stenedione to estrone in postmenopausal women with and without endometrial cancer. Am J Obstet Gynecol 130: 448, 1978
121. Ackerman GE, Smith ME, Mendelson CR, MacDonald PC, Simpson ER: Aromatization of androstenedione by human adipose tissue stromal cells in monolayer culture. J Clin Endocrinol Metab 53:412, 1981
122. Cleland WH, Mendelson CR, Simpson ER: Aromatase ac- tivity of membrane fractions of human adipose tissue, stromal cells and adipocytes. Endocrinology 113:2155, 1983
123. Hemsell DL, Grodin JM, Brenner PF, Siiteri PK, Mac- Donald PC: Plasma precursors of estrogen. II. Correlation of the extent of conversion of plasma androstenedione to estrone with age. J Clin Endocrinol Metab 38:476, 1974
124. Forney JP, Milewich L, Chen GT, Garlock GL, Schwarz BE, Edman CD, MacDonald PC: Aromatization of andro- stenedione to estrone by human adipose tissue in vitro. Correlation with adipose tissue mass, age, and endome- trial neoplasia. J Clin Endocrinol Metab 53:192, 1981
125. Cleland WH, Mendelson CR, Simpson ER: Effects of aging and obesity on aromatase activity of human adipose cells. J Clin Endocrinol Metab 60:174, 1985
126. MacDonald PC, Edman CD, Kerber IJ, Siiteri PK: Plasma precursors of estrogen. III. Conversion of plasma dehydroisoandrosterone to estrogen in young nonpreg- nant women. Gynecol Invest 7:165, 1976
127. Rizkallah TH, Tovell HMM, Kelly WG: Production of es- trone and fractional conversion of circulating androstene- dione to estrone in women with endometrial carcinoma. J Clin Endocrinol Metab 40:1045, 1975
128. Takaki NK, Siiteri PK, Williams J, Tredway DR, Lewis SB, Daane TA: The effect of weight loss on peripheral es- trogen synthesis in obese women. Int J Obes 2:386, 1978
129. Longcope C, Layne DS, Tait JF: Metabolic clearance rates
and interconversions of estrone and 17-6-estradiol in nor- mal males and females. J Clin Invest 47:93, 1968
130. Fishman J, Boyar RM, Hellman L: Influence of body weight on estradiol metabolism in young women. J Clin Endocrinol Metab 41:989, 1975
131. Schneider J, Bradlow HL, Strain G, Lebin J, Anderson K, Fishman J: Effect of obesity on estradiol metabolism: Decreased formation of nonuterotropic metabolites. J Clin Endocrinol Metab 56:973, 1983
132. Flood C, Pratt JH, Longcope C: The metabolic clearance and blood production rates of estriol in normal, non-preg- nant women. J Clin Endocrinol Metab 42:1, 1976
133. Roncari DAK, Van RLR: Promotion of human adipocyte precursor replication by 17-6-estradiol in culture. J Clin Invest 62:503, 1977
134. de Waard F, Poortman J, de Pedro-Alvarez Ferrero M, Baanders-van Halewisn EA: Weight reduction and oestro- gen excretion in obese post-menopausal women. Maturi- tas 4:155, 1982
135. O’Brien TJ, Higashi M, Kanasugi H, Gibbons WE, Mar- row CP: A plasma/serum estrogen-binding protein dis- tinct from testosterone-estradiol-binding globulin. J Clin Endocrinol Metab 54:793, 1982
136. Anderson DC: Sex-hormone-binding globulin. Clin Endo- crinol 3:69, 1974
137. Pardridge WM, Mietus LJ, Frumar AM, Davidson BJ, Judd HL: Effects of human serum on transport of testos- terone and estradiol into rat brain. Am J Physiol 239: E103, 1980
138. Nisker JA, Hammond GL, Davidson JB, Frumar AM, Ta- kaki NK, Judd HL, Siiteri PK: Serum sex hormone-bind- ing globulin capacity and the percentage of free estradiol in postmenopausal women with and without endometrial carcinoma. Am J Obstet Gynecol 138:638, 1980
139. Vermeulen A, Verdonck L, Van Der Straeten M, Orie N: Capacity of the testosterone-binding globulin in human plasma and influence of specific binding of testosterone on its metabolic clearance rate. J Clin Endocrinol Metab 28: 1470, 1969
140. Doe RP, Mellinger GT, Swaim WR, Coseal US: Estrogen dosage effects on serum proteins: a longitudinal study. J Clin Endocrinol Metab 27:1081, 1967
141. Musa BU, Doe RP, Coseal US: Serum protein alterations produced in women by synthetic estrogens. J Clin Endo- crinol Metab 27:1463, 1967
142. Laurell C-B, Kullander S, Thorell J: Effect of administra- tion of a combined estrogen-progesterone contraceptive on the level of individual plasma protein. Scand J Clin Lab Invest 21:337, 1968
143. Pearlman WH, Crepy O, Murphy M: Testosterone-bind- ing levels in the serum of women during the normal men- strual cycle, pregnancy, and the post-partum period. J En- docrinol Metab 27:1012, 1967
144. Wu C-H, Motohashi T, Abdel-Rahman HA, Flickinger GL, Makhail G: Free and protein-bound plasma estradiol 17-a during the menstrual cycle. J Clin Endocrinol Metab 43:436, 1976
145. Dickinson P, Zineman HH, Swaim WR, Doe RP, Coseal US: Effects of testosterone treatment on plasma proteins and aminoacids in men. J Clin Endocrinol Metab 29:837, 1969
146. Cunningham SK, Loughlin T, Culliton M, McKenna TJ: Plasma sex hormone-binding globulin levels decrease dur-
ing the second decade of life irrespective of pubertal sta- tus. J Clin Endocrinol Metab 58:915, 1984
147. Siiteri PK, Hammond GL, Nisker JA, Tataki N: Adrenal androgen, metabolism and conversion in humans. In Adrenal Androgens, Edited by AR Genazzani, JHH Thijs- sen, PK Siiteri. New York, Raven Press, 1980, p 109
148. Lee IR, Greed LC, Hahnel R: Comparative measurements of plasma-binding capacity and concentration of human sex hormone binding globulin. Clin Chim Acta 137:131, 1984
149. Reed MJ, Cheng RW, Simmonds M, Richmond W, James VHT: Dietary lipids: An additional regulator of plasma levels of sex hormone binding globulin. J Clin Endocrinol Metab 64:1083, 1987
150. Arendt EC, Pattee CJ: Studies on obesity. I. Metab 16:367, 1956
151. Sims EAH, Danforth E, Jr, Horton ES, Bray GA, Glennon JA, Salans LB: Endocrine and metabolic effects of experi- mental obesity in man. Rec Prog Horm Res 29:457, 1973
152. Pagano G, Cassader M, Bozzo C, Masciola P, Trovati M, Lenti G: Insulin resistance in human obesity: in vivo stud- ies by “insulin clamping” and in vitro by insulin binding and biologic activity on isolated adipocytes. In Obesity: Pathogenesis and Treatment, Serono Symposium, Vol 28, Edited by G Enzi, G Crepaldi, G Pozza, AE Renold. New York, Academic Press, 1981, p 175
153. Debry G, Martin JM, Pointel JP, Drouin P, Megean L: Comparative study of glucose tolerance and stimulated in- sulin secretion in obesity by oral and intravenous glucose tolerance and tolbutamide tests. In Medical Complica- tions of Obesity, Serono Symposia, Vol 26, Edited by M Mancini, B Lewis, F Contaldo. New York, Academic Press, 1979, p 59
154. Golay A, Swislocki ALM, Chen Y-D I, Jaspan JB, Reaven GM: Effect of obesity on ambient plasma glucose, free fatty acid, insulin, growth hormone, and glycogen concen- trations. J Clin Endocrinol Metab 63:481, 1986
155. Koivisto VA, Yki-Jarvinen H, Hartling SG, Pelkonen R: The effect of exogenous hyperinsulinemia on proinsulin secretion in normal man, obese subjects, and patients with insulinoma. J Clin Endocrinol Metab 63:1117, 1986
156. Kolterman OG, Insel J, Saekow M, Olefsky JM: Mecha- nisms of insulin resistance in human obesity. J Clin Invest 65:1272, 1980
157. Grunberger G, Taylor SI, Dons RF, Gorden P: Insulin re- ceptors in normal and diseased states. Clin Endocrinol Metab 12:191, 1983
158. Bagdade JD, Bierman EL, Porte D, Jr: The significance of basal insulin levels in the evaluation of insulin response to glucose and diabetic and nondiabetic subjects. J Clin Invest 46:1549, 1967.
159. El-Khodary AZ, Ball MF, Oweiss IM, Canary JJ: Insulin secretion in body composition in obesity. Metabolism 21: 641, 1972
160. Olefsky J, Reaven JM, Farquhar JW: Effects of weight re- duction on obesity. J Clin Invest 53:64, 1974
161. Bar RS, Gorden P, Roth J, Khn CR, Mayts PD: Fluctua- tions in the affinity and concentration of insulin receptors on circulating monocytes of obese patients. J Clin Invest 58:1123, 1976
162. Burghen GA, Givens JR, Kitabchi AE: Correlation of hy-
perandrogenism with hyperinsulinism in polycystic ovar- ian disease. J Clin Endocrinol Metab 50:113, 1980
163. Stuart CA, Prince MJ, Peters EJ, Meyer WJ III: Hyperin- sulinemia and hyperandrogenemia: in vivo androgen re- sponse to insulin infusion. Obstet Gynecol 69:921, 198
164. Peiris AN, Mueller RA, Struve MF, Smith GA, Kisseb AH: Relationship of androgenic activity to splanchnic in- sulin metabolism and peripheral glucose utilization in pre- menopausal women. J Clin Endocrinol Metab 64:162, 1987
165. Zumoff B, Strain GW, Kream J, Levin J, Fukushima DK: Subnormal 24-hour mean plasma LH concentration and elevated plasma FSH/LH ratio in obese premenopausal women. J Reprod Med 28:843, 1983
166. Newmark SR, Rossini AA, Aftolin FI, Todd R, Rose LI, Cahill GF, Jr: Gonadotropin profiles in fed and fasted obese women. Am J Obstet Gynecol 133:75, 1979
167. Beitins IZ, Shah A, O’Loughlin K, Johnson L, Ostrea TR, Van Wart J, McArthur JW: The effects of fasting on se- rum and urinary gonadotropins in obese postmenopausal women. J Clin Endocrinol Metab 51:26, 1980
168. Copinschi G, De Laaet M-H, Brion JP, Leclercq R, L’Agrmite M, Robyn C, Virasoro E, Van Cauter E: Simul- taneous study of cortisol, growth hormone and prolactin nyctohemeral variations in normal and obese subjects: in-
fluence of prolonged fasting in obesity. Clin Endocrinol 9: 15, 1978
169. Kopelman PG, Pilkington TRE, White N, Jeffocate SL: Impaired hypothalamic control of prolactin secretion in massive obesity. Lancet 1:747, 1979
170. Donders SHJ, Pieters JGGM, Heevel JG, Ross HA, Smals AGH, Kloppenborg PWC: Disparity of thyrotropin (TSH) and prolactin responses to TSH-releasing hormone in obesity. J Clin Endocrinol Metab 61:56, 1985
171. Cooper DS, Ridgway EC, Kliman B, Kjellberg RN, Maloof F: Metabolic clearance and production rates of prolactin in man. J Clin Invest 64:1669, 1979
172. Kwa HG, Bulbrook RD, Clenton F, Verstraeten AA, Hay- ward JL, Wang DY: An abnormal early evening peak of plasma prolactin in nulliparous and obese post-meno- pausal women. Int J Cancer 22:691, 1978
173. Kalucy RS, Crisp AH, Chard T, McNeilly A, Chen CNN, Lacey JH: Nocturnal hormonal profiles in massive obe- sity, anorexia nervosa in normal females. J Psychosom Res 20:595, 1976
174. Cavagnini F, Maraschini C, Pinto M, Dubini A, Polli EE: Impaired prolactin secretion in obese patients. J Endocri- nol Invest 4:149, 1981
175. Wilcox RG: Triiodothyronine, TSH, and prolactin in obese women. Lancet 1:1027, 1977
Received September 27, 1988.
Reprint requests: Ricardo Azziz, M.D., Assistant Professor, Department Obstetrics and Gynecology, The University of Alabama at Birmingham, 549 Old Hillman Building, Birmingham, Alabama 35294.
Supported in part by National Cancer Institute grant CA-28103 of The Clinical Nutrition Research Unit of the University of Alabama at Birmingham.