Daytime titers of testosterone, LH, estrone, estradiol, and testosterone-binding protein: acute effects of LH and LH-releasing hormone in men

Bioavailable Testosterone Linearly Declines Over A Wide Age Spectrum in Men and Women From The Baltimore Longitudinal Study of Aging

BACKGROUND

Age-related changes in testosterone levels in older persons and especially in women have not been fully explored. The objective of this study was to describe age-related trajectories of total testosterone (TT), ammonium sulfate precipitation-measured bioavailable testosterone (mBT), and sex hormone-binding glycoprotein (SHBG) in men and women from the Baltimore Longitudinal Study of Aging, with special focus on the oldest adults.

METHODS

Participants included 788 White men and women aged 30-96 years with excellent representation of old and oldest old, who reported not taking medications known to interfere with testosterone. Longitudinal data were included when available. TT, mBT, and SHBG were assayed. Age-related trajectories of mBT were compared with those obtained using calculated bioavailable testosterone (cBT). Generalized least square models were performed to describe age-related trajectories of TT, mBT, and SHBG in men and women.

RESULTS

mBT linearly declines over the life span and even at older ages in both sexes. In men, TT remains quite stable until the age of 70 years and then declines at older ages, whereas in women TT progressively declines in premenopausal years and slightly increases at older ages. Differences in age-related trajectories between total and bioavailable testosterone are only partially explained by age changes in SHBG, whose levels increases at accelerated rates in old persons. Noteworthy, although mBT and cBT highly correlated with one another, mBT is a much stronger correlate of chronological age than cBT.

CONCLUSION

In both men and women, mBT linearly declines over the life span and even at old ages. Its relationship with age-related phenotypes should be further investigated.

Adolescent endogenous sex hormones and breast density in early adulthood

INTRODUCTION

During adolescence the breasts undergo rapid growth and development under the influence of sex hormones. Although the hormonal etiology of breast cancer is hypothesized, it remains unknown whether adolescent sex hormones are associated with adult breast density, which is a strong risk factor for breast cancer.

METHODS

Percentage of dense breast volume (%DBV) was measured in 2006 by magnetic resonance imaging in 177 women aged 25-29 years who had participated in the Dietary Intervention Study in Children from 1988 to 1997. They had sex hormones and sex hormone-binding globulin (SHBG) measured in serum collected on one to five occasions between 8 and 17 years of age. Multivariable linear mixed-effect regression models were used to evaluate the associations of adolescent sex hormones and SHBG with %DBV.

RESULTS

Dehydroepiandrosterone sulfate (DHEAS) and SHBG measured in premenarche serum samples were significantly positively associated with %DBV (all P trend ≤0.03) but not when measured in postmenarche samples (all P trend ≥0.42). The multivariable geometric mean of %DBV across quartiles of premenarcheal DHEAS and SHBG increased from 16.7 to 22.1 % and from 14.1 to 24.3 %, respectively. Estrogens, progesterone, androstenedione, and testosterone in pre- or postmenarche serum samples were not associated with %DBV (all P trend ≥0.16).

CONCLUSIONS

Our results suggest that higher premenarcheal DHEAS and SHBG levels are associated with higher %DBV in young women. Whether this association translates into an increased risk of breast cancer later in life is currently unknown.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov Identifier, NCT00458588 April 9, 2007; NCT00000459 October 27, 1999.

Testosterone and bioavailable testosterone help to distinguish between mild Cushing's syndrome and polycystic ovarian syndrome

Women with Cushing's syndrome (CS) and polycystic ovarian syndrome (PCOS) may present with similar symptoms. Subjects with mild CS lack clinical stigmata of classical CS and often have normal laboratory tests measuring hypercortisolism. Thus, distinguishing mild CS from PCOS may be difficult. We hypothesized that either total testosterone (TT) or bioavailable testosterone (BT) levels or the calculation of the free androgen index (FAI) would be low in patients with mild CS and elevated in patients with PCOS, and could help differentiate the two conditions. TT, BT, and FAI were measured in a group of 20 patients of reproductive age with mild CS and 20 PCOS patients matched for age and BMI. We used receiver operator characteristic (ROC) curves to assess the sensitivity and specificity of these measurements for the diagnosis of CS. TT (p<0.0001), BT (p=0.02), and FAI (p=0.003) were significantly elevated in PCOS patients compared to mild CS patients. Sex hormone-binding globulin was similar in both groups. The optimal cut-point for TT was 1.39 nmol/L, yielding a sensitivity of 95% and a specificity of 70%. The cut-point for BT was 0.24 nmol/L, resulting in a sensitivity of 75% and a specificity of 80%. The cut-point for FAI was 5.7, with a sensitivity of 88% and a specificity of 60%. We conclude that TT levels may be useful to discriminate between mild CS and PCOS. In patients with signs and symptoms consistent with CS and PCOS, a TT level of <1.39 nmol/L warrants a workup for CS.

Bioavailable Testosterone Should be Used for the Determination of Androgen Levels in Infertile Men

PURPOSE

We determined the relationship between total testosterone and bioavailable testosterone in men presenting with infertility. In addition, the effects of body mass index and age on testosterone levels were examined. To determine if total testosterone measurements are an accurate reflection of tissue available testosterone in infertile men, levels of total testosterone were compared to bioavailable testosterone levels.

MATERIALS AND METHODS

Males presenting with infertility were studied. A total of 73 patients underwent complete history and physical examination. Serum levels of total testosterone and bioavailable testosterone were measured as a morning sample in all patients. Patients were classified as having low, normal or high levels of total or bioavailable testosterone. To determine the effect of obesity, patient weight was converted to body mass index for analysis.

RESULTS

Of 73 patients evaluated 34 (47%) had low total testosterone levels while only 19 (26%) had low bioavailable testosterone levels. The discrepancy between total testosterone and bioavailable testosterone was even greater in men older than 40 years with 10 of 17 (59%) having low total testosterone levels and 8 (80%) having normal bioavailable testosterone levels. Body mass index negatively correlated with total testosterone and bioavailable testosterone levels.

CONCLUSIONS

Testosterone status should be determined by the measurement of bioavailable testosterone when evaluating infertile males.

A study of the relative roles of follicle-stimulating hormone and luteinizing hormone in the regulation of testicular inhibin secretion in the rhesus monkey (Macaca mulatta)

The purpose of this study was to examine the relative roles of FSH and LH in stimulating testicular inhibin secretion in the male rhesus monkey. Recombinant human (rh) FSH and rhCG were used as the gonadotropic stimuli, and juvenile rhesus monkeys, in which the endocrine activity of the pituitary-testicular axis was being driven in an adult manner with an intermittent i.v. GnRH infusion, were studied. Immunoactive inhibin levels were measured by the Monash RIA. Initiation of an intermittent i.v. infusion of rhFSH (10 IU every 3 h) resulted, after a delay of 5-6 h, in a progressive increase in the concentrations of immunoactive inhibin, which achieved, after 48 h of stimulation, a value twice that observed during vehicle treatment. Gel filtration chromatography revealed that the FSH-induced elevation in immunoactive inhibin was the result of an increase in three distinct mol wt fractions: peak I (100 kDa), peak II (50-60 kDa), and peak III (31 kDa). Although peak III accounted for most of the inhibin immunoactivity in vehicle-treated animals, peaks I and II were most responsive to FSH stimulation. Application of recently developed enzyme-linked immunosorbent assays for inhibin B and pro-alpha-C-related peptides provided additional insights into the nature of the FSH-sensitive forms of circulating immunoactive inhibin. Most notably, the 31-kDa fraction (peak III) was comprised of inhibin B and pro-alpha-C. In contrast to FSH stimulation, an intermittent infusion of rhCG (40 IU every 3 h), which markedly elevated testicular testosterone secretion, failed to increase immunoactive inhibin concentrations. These findings indicate that various forms of immunoactive inhibin are present in the circulation of the rhesus monkey, and that in this species, FSH is the principal stimulus of the secretion of testicular inhibins, including inhibin B. Additionally, they further underline the importance of the FSH-inhibin feedback loop in governing testicular function in primates.

5-alpha-reductase activity and risk of prostate cancer among Japanese and US white and black males

The incidence of prostate cancer varies widely between countries and ethnic groups. Black-Americans have the highest incidence rates world wide, whereas native Japanese have among the lowest. The reasons for this risk differential are unknown, although we have previously shown that higher circulating testosterone concentrations in young adult black men compared with young adult white men may explain the underlying differences in subsequent prostate cancer incidence between these two populations. We have now compared serum testosterone concentrations in young adult Japanese men with those of young adult whites and blacks, but found no significant differences. However, these white and black men had significantly higher values of 3 alpha, 17 beta androstanediol glucuronide (31% and 25% higher, respectively) and androsterone glucuronide (50% and 41% higher, respectively) than Japanese subjects. These two androgens are indices of 5 alpha-reductase activity. Our results raise the possibility that reduced 5 alpha-reductase activity has a role in producing the low prostate cancer incidence rates among Japanese. This finding may have important implications for prostate cancer prevention.

Hormone load tests in infertile male patients

The recognition that discreet hormonal abnormalities may cause ovulation disorders in women suggested that the male partner of infertile women might also suffer from unrecognized hormonal dysfunction amendable to substitution therapy. We obtained a combined stimulation test with gonadotropin-releasing hormone (GnRH), thyreotropin-releasing hormone (TRH), and ACTH in 225 males with childless spouses, when the couple sought to have children for at least one year. The following hormone levels were determined: estradiol (E), thyroid-stimulating hormone (TSH), prolactin, testosterone (T), dihydrotestosterone (DHT), androstenedione(A), 17-OH-pregnenolone (17-OH-Preg), 17-OH-progesterone (17-OHP), dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), cortisone (F), and 21-desoxycortisone (21DF). Basal and stimulated, and adrenal-testicular steroids with and without ACTH stimulation failed to demonstrate a relevant relationship to semen parameters. Gonadotropin levels had a significant negative correlation to all important semen parameters (testicular volume, sperm count, motility, morphology, and vitality) and were positively correlated to spermiogenetic defects. Stimulated LH values were more clearly associated with spermiogenetic defects than basal LH. Nonetheless, basal FSH concentrations were more informative than LH. Stimulated prolactin values were positively correlated with both gonadotropin and with sperm morphology. E concentrations had a significant positive correlation with both basal and poststimulation DHEAS values, and showed a highly negative correlation with sperm count, morphology, and vitality. In comparison, good sperm parameters were associated with high poststimulation T concentrations. The results of this study suggest that basal FSH and E concentrations, as well as the stimulated LH, T, and prolactin determinations, should be included in the evaluation of male sterility.

Serum oestrogen levels in postmenopausal women: comparison of American whites and Japanese in Japan

Serum oestrone (E1), oestradiol (E2) and sex hormone binding globulin (SHBG) levels were studied in postmenopausal Japanese women in Japan (n = 91) and postmenopausal American white women (n = 38). The Japanese women were deliberately chosen to be from a rural agricultural area in order to get samples which represent as closely as possible the traditional Japanese 'lifestyle' that gave rise to the low rates of breast cancer in Japan. E1 levels were 47%, and E2 levels 36%, greater in the American women; these differences were only reduced to 43% and 27% after adjustment for the lower weight of the Japanese. These results were all statistically highly significant. There was little difference in SHBG levels between the Japanese and the American women. These results for E1 and E2 could be an important part of the explanation why Japanese and American breast cancer rates continue to diverge further after the menopause.

Cigarette smoking in pregnancy results in marked decrease in maternal hCG and oestradiol levels

We have examined serum levels of oestradiol (E2), sex-hormone binding globulin (SHBG) and human chorionic gonadotrophin (hCG) during early pregnancy in relation to smoking status at the time of sampling in a series of 147 women. Smoking was associated with significantly depressed serum levels of E2, SHBG and hCG: in smokers, E2 levels were on average 17.6% lower (P = 0.037), SHBG levels were 12.4% lower (P = 0.15), and hCG levels were 21.5% lower (P = 0.044). There appeared to be a steady decline in these values with increasing cigarette consumption. These lower hormone levels in smokers may explain certain adverse effects of smoking in pregnancy.

Vasectomy, cigarette smoking, and age at first sexual intercourse as risk factors for prostate cancer in middle-aged men

A population-based case-control study was conducted in men aged 60 or less to assess the risk of prostate cancer associated with vasectomy and other factors. Data were obtained from 216 case-control pairs by telephone interviews; this number represented 55% of all eligible cases. The matched pairs relative risk (RR) for vasectomy in ever married men was 1.4 with a 95% confidence interval (CI) of 0.9-2.3. There was a positive association between the number of years since vasectomy and prostate cancer risk (1-sided P = 0.01). Early age at first sexual intercourse was associated with increased prostate cancer risk (age less than 17 vs. 21+, RR = 2.3, 95% CI = 1.3, 4.0) but there were no consistent associations with number of sexual partners or frequency of sexual intercourse. Cigarette smoking was also associated with increased risk of prostate cancer (RR = 1.9, 95% CI = 1.2, 3.0) and there was a positive dose-response relationship with years of smoking (1-sided P = 0.001). We discuss the possible implication of the low response rate on each of these findings. To determine whether the association with vasectomy might have a hormonal basis, we compared levels of testosterone (T) and testosterone binding globulin-binding capacity (TeBG-bc) in 33 of the vasectomized control men with levels in 33 non-vasectomized controls of the same age, weight and height. T levels were higher in vasectomized than in non-vasectomized controls (1-sided P = 0.06). The ratio of T to TeBG-bc (an index of bioavailable T) was 13.5% higher in vasectomized men (1-sided P = 0.03).

Hyperemesis gravidarum in relation to estradiol levels, pregnancy outcome, and other maternal factors: a seroepidemiologic study

Two studies were conducted to assess factors associated with increased risk of hyperemesis gravidarum during pregnancy with data and serum samples collected from participants in the Collaborative Perinatal Study. In the case-control study, 419 pregnant women with hyperemesis gravidarum were matched on medical center, date of study registration, and race with 836 pregnant women who did not vomit during the index pregnancy. Younger age, nulliparity, and high body weight were significantly associated with increased risk of hyperemesis. Women with hyperemesis had significantly reduced risk of fetal loss; however, their infants had higher risk of central nervous system malformations. In the second study, first-trimester pregnancy hormones were measured in the serum of 35 women with hyperemesis and 35 control women who were individually matched to cases on age, parity, and medical center. After adjusting for length of gestation, mean levels of total estradiol were 26% higher and mean levels of sex hormone binding-globulin binding capacity were 37% higher in patients with hyperemesis gravidarum than in control subjects. These differences were statistically significant. Although human chorionic gonadotropin concentrations were higher in control pregnancies, the differences were not statistically significant. The average amount of estradiol that was nonprotein bound (adjusted for length of gestation) was also higher in patients than in control subjects. These results are consistent with the hypothesis that elevated estrogen levels are responsible for excessive vomiting in pregnancy.

Breast stimulation in cycling women, pregnant women and a woman with induced lactation: pattern of release of oxytocin, prolactin and luteinizing hormone

Levels of oxytocin (OT) and PRL were measured in plasma drawn before and during intermittent mechanical pump and tactile stimulation of the breast in five normal cycling women and 19 women in the third trimester of pregnancy. OT was significantly increased above baseline in response to breast stimulation in two of five cycling women and PRL increased in one of the two OT responders. In pregnant women, mean OT post nipple stimulation was significantly higher than pre nipple stimulation whereas PRL did not increase significantly. The response of OT to nipple stimulation occurred in 18 of 19 pregnant women compared to only two of five normal cycling women but the magnitude of the OT response in pregnant women was less than in cycling women or post-partum lactating women previously studied in this laboratory. In one non post-partum woman who induced lactation for the purpose of breast-feeding an adopted infant, OT and PRL were measured before and during mechanical pump and tactile stimulation before initiation of breast-feeding. OT increased during mechanical pump and tactile stimulation of the breast, as well as suckling, whereas PRL increased only in response to suckling. Levels of LH were measured in plasma every 20 min for 160 min at the following times: before initiation of breast-feeding, during induced lactation while breast-feeding, and 30 d after discontinuation of breast-feeding. Despite the development of oligomenorrhoea during the period of breast-feeding, levels of progesterone were not suppressed and LH was released in a normal pulsatile fashion.

Testicular steroid response to continuous and pulsatile intravenous luteinizing hormone-releasing hormone administration in normal men

In 18 healthy normal men Leydig cell response was examined following intravenous luteinizing hormone-releasing hormone (LH-RH) administration under standardized conditions. The same total amount of LH-RH was administered for 3 hours both in a continuous (1 microgram/min; C (1,1)) and in a pulsatile fashion, by giving a 20 micrograms dose at 20 minutes intervals, P (20, 20), and a 60 micrograms dose at 60 minutes intervals, P (60, 60). Following the different modes of LH-RH administration which all caused 3-4 fold elevations of the mean endogenous luteinizing hormone (LH) concentrations and 1.7-2 fold elevations of the mean follicle-stimulating hormone (FSH) serum levels, an overt increase of the mean testosterone (T) levels was noticed up to 1.5 X the baseline value. No difference was observed in the total amount of T release among the investigated groups. The patterns of the T response, however, clearly differed from one another with a rapid increase, during the C (1, 1) and the P (20, 20) LH-RH administration, and a delayed but persistent T increase in the P (60, 60) experiment. The mean 17-hydroxyprogesterone (17-OHP) concentrations demonstrated a similar course to T in the P (60,60) experiment, while significant increases of the oestradiol (E 2) levels were never observed in all three experiments. In view of the comparable LH and FSH increments in response to LH-RH administration in either experiment the differences in T responses may be explained by assuming a direct effect of LH-RH on Leydig cell steroidogenesis in the men.

The gonadotropin-suppressive activity of androgen is increased in elderly men

The influence of aging on the responsiveness to sex steroid hormones in men was studied by comparing circulating gonadotropin concentrations, pulsatile LH release, and sex hormone-binding globulin (TeBG) levels. This was done before and during a four-day continuous infusion of testosterone (T) (7.5 mg/d), dihydrotestosterone (DHT) (7.0 mg/d), or estradiol (E2) (45 micrograms/d) in young adult men, ages 18 to 32, and healthy elderly men, ages 65 to 80. DHT reduced mean serum LH and FSH levels as well as the frequency of spontaneous LH secretory episodes to a greater extent (p less than 0.05) in old men than in young men. T administration also reduced serum LH levels more in aged than in young men (P less than 0.05); however, this difference was less pronounced than for DHT. During T infusion, the decrease in serum FSH levels was similar in the two groups. Spontaneous LH pulse amplitude also declined during both T and DHT infusion in aged, but not in young men. By contrast, infusion of E2 reduced both serum LH and FSH levels comparably in aged and young men. DHT infusion also reduced serum TeBG levels equally in old and young men. Finally, each steroid infusion produced comparable mean circulating levels of T, DHT, and E2 in both groups. These data indicate that elderly men are more responsive than are young men to the gonadotropin-suppressive effects of androgen, but not to DHT effects on circulating TeBG levels. The more pronounced deceleration of spontaneous LH secretory episodes during DHT infusion in aged men provides evidence for an alteration in hypothalamic function in male senescence.

Differential effect of luteinizing hormone-releasing hormone infusion on testicular steroids in normal men and patients with idiopathic oligospermia

Basal serum gonadotropin levels in 11 oligospermic men were significantly higher than in 9 euspermic control subjects, although most were still in the normal range. Basal serum testosterone (T), 17-hydroxyprogesterone (17-OHP), and estradiol levels and their ratios did not differ significantly. Continuous luteinizing hormone-releasing hormone (LH-RH) infusion (1 microgram/minute for 180 minutes) during integrated blood sampling evoked similar gonadotropin responses in both groups but had a differential effect on T: in the control subjects T increased (P less than 0.01) within 15 minutes to 1.5 times baseline, whereas in the oligospermic men T decreased (P less than 0.01). From 60 minutes on, however, T also significantly rose in the oligospermic men, but the maximum increment was about half lower (P less than 0.01) than in the euspermic men, despite virtually similar rises in 17-OHP. Only in the oligospermic men did the 17-OHP/T ratio increase (P less than 0.02) during LH-RH, which is compatible with the occurrence of a 17,20-lyase block. Serum estradiol did not increase in either group. In conclusion, continuous LH-RH infusion uncovers an intrinsic difference in acute Leydig cell stimulation between euspermic and oligospermic men.

Basal and adrenocorticotropic hormone-stimulated serum 17 alpha-hydroxyprogesterone in men with idiopathic infertility

Basal serum 17 alpha-hydroxyprogesterone (17-OHP) concentrations and the 17-OHP response to acute adrenocorticotropic hormone administration were studied in infertile men with idiopathic oligospermia to determine the prevalence of attenuated 21-hydroxylase deficiency. Mean (+/- standard error of the mean) basal serum 17-OHP levels in 50 infertile men (1.17 +/- 0.06 ng/ml) and 25 normal volunteers (1.09 +/- 0.08 ng/ml) were indistinguishable (not significant). However, two infertile men had 17-OHP levels which were above the normal range. Following the intravenous administration of 0.25 mg of synthetic adrenocorticotropic hormone (cosyntropin) to these two men and to eight additional infertile men, the mean increase in 17-OHP concentrations was 0.84 +/- 0.15 ng/ml, a response which was similar to that of normal men (0.94 +/- 0.26 ng/ml). No patient demonstrated the minimum fourfold rise in 17-OHP previously reported in men with attenuated 21-hydroxylase deficiency, suggesting the absence of this disorder among these subjects. This study suggests that subtle 21-hydroxylase deficiency is rare among infertile men with idiopathic infertility.

Estrogens and cytosolic estrogen receptors in aged male rats

To determine whether estrogens may play a role in the decline in Leydig cell function in aged rats, plasma levels of testosterone, estradiol, and estrone; intratesticular concentrations of testosterone and estradiol; as well as cytosolic estrogen receptors were studied. Plasma and intratesticular testosterone levels were reduced in aged Sprague-Dawley rats, but circulating levels of estrone and estradiol, as well as intratesticular estradiol concentrations, were similar in aged and young-adult animals. Furthermore, in both testicular and kidney cytosol, the dissociation constants for estradiol and the concentrations of estradiol binding sites remained unchanged during aging. These data suggest that estrogens are unlikely to be important mediators of the reduced Leydig cell function in old rats.

Studies of the human testis. XVI. Evaluation of multiple indexes of testicular function in relation to advanced age, idiopathic oligospermia, or varicocele

Testicular function was evaluated by morphologic and biochemical methods in 11 infertile men with idiopathic oligospermia, 12 men with varicocele, and 14 elderly men. The results indicate the presence of two separate subgroups with idiopathic oligospermia with distinct endocrine and morphologic parameters and suggest the involvement of different pathogenetic factors for testicular disorders among these four groups. Biochemical indexes provide further confirmation of the validity of the Leydig cell cluster index (number of Leydig cell clusters per tubular section) as a useful evaluation guide. The results support the importance of combined studies of circulating hormones and testicular histologic features in providing insight into spermatogenic disorders. Recognition of etiologic diversity is an essential basis for further efforts to delineate and apply current or new hormonal techniques for therapy.

Effect of long-term physical training on plasma testosterone, androstenedione, luteinizing hormone and sex-hormone-binding globulin capacity

The effect of 6-months' physical training on plasma testosterone, androstenedione and luteinizing hormone levels and the binding capacity of sex-hormone-binding globulin (SHBG capacity) were studied in thirty-nine army recruits. Highly significant increases in mean plasma testosterone (21%), androstenedione (25%) and LH (25%) were observed during the training period and were associated with a mean 16% increase in the estimated maximal oxygen uptake. The mean increases in hormone levels tended to be greater in the well conditioned group than in the poorly conditioned group. The mean ratio of testosterone to SHBG capacity increased by 32% (P less than 0.05), which may be in relationship with the various training-induced effects.

Effect of infusion of gonadotropin releasing hormone upon plasma concentrations of sex hormones in prepubertal and pubertal males

Plasma testosterone (T), dihydrotestosterone (DHT), 17-hydroxyprogesterone (17OHP), androstenedione (A), estradiol (E2), and dehydroepiandrosterone sulfate (DHAS) were measured by radioimmunoassay after celite chromatography prior to and after a 3-hour infusion of the synthetic gonadotropin releasing factor, GnRH, in normal prepubertal and pubertal boys. Plasma T levels rose (p less than 0.001) in the pubertal but not prepubertal boys. 17OHP concentrations increased in those boys who had an increment of T. A, DHT, E2 or DHAS levels did not increase after GnRH. Basal levels of T, DHT, A and DHAS correlated with the peak and mean serum LH levels attained during the GnRH infusion. These data confirm the greater Leydig cell responsivity to transient rises of endogenous gonadotropin in pubertal males and also suggest that there may be a relationship between adrenal androgen production and maturation of the hypothalamic-pituitary-gonadal system.