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Regulation of FSH secretion in the male involves a complex balance between stimulation by GnRH from the hypothalamus, inhibitory feedback by sex steroids (T and E2) and inhibin B (Inh B) from the gonads, and autocrine/paracrine modulation by activin and follistatin within the pituitary. The aim of the present study was to delineate the feedback control of FSH in the human male with specific reference to the relative roles of sex steroids vs. Inh B. Two experimental human models were used: 1) normal (NL) men subjected to acute sex steroid withdrawal (-T, -E2, + Inh B), and 2) functional castrate males (-T, -E2, -Inh B). Nine NL men (age range, 25-45 yr) and three castrate males (age range, 23-47 yr) were studied. The NL men underwent acute sex steroid suppression using high dose ketoconazole (1-g loading dose, followed by 400 mg, orally, four times daily for 150 h). Gonadotropin secretion was characterized by frequent blood sampling every 10 min for 12 h at baseline and on d 3 and 6 of sex steroid ablation. In the three castrate subjects, blood sampling was performed every 5 min for 24 h 8 wk after discontinuing androgen replacement therapy. In the NL men, treatment with ketoconazole resulted in a decline to castrate levels in T (451 +/- 20 to 38 +/- 7 ng/dl; P < 0.0005) and E2 (39 +/- 4 to 15 +/- 2 pg/ml; P < 0.005) and a modest, but significant, decline in Inh B levels, which remained within the normal range (183 +/- 19 to 136 +/- 13 pg/ml; P < 0.005). This suppression of sex steroids was associated with a more marked increase in mean LH (9.5 +/- 0.9 to 24.9 +/- 2.0 IU/liter; P < 0.0001) than FSH levels (5.1 +/- 0.7 to 10.0 +/- 1.5 IU/liter; P < 0.005), with the latter not exceeding the normal adult male range. The castrate subjects had a mean T level of 66 +/- 8 ng/dl, an E2 level of 20 +/- 1 pg/ml, and undetectable Inh B levels. Despite a similar sex steroid milieu, the mean FSH levels observed in NL men after acute sex steroid ablation were approximately 6-fold lower than those seen in the castrate subjects (10.0 +/- 1.5 vs. 59.5 +/- 17.7 IU/liter; P < 0.0005). In contrast, mean LH levels in the NL men were less than 3-fold lower than those in castrate subjects (24.9 +/- 2.0 vs. 66.8 +/- 20.1 IU/liter; P < 0.005). From this human model of acute sex steroid withdrawal, we conclude that Inh B is likely to be the major feedback regulator of FSH secretion in the human male.

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The physical changes that herald the onset of puberty result from the combination of adrenarche and gonadarche. To examine adrenal maturation and associated changes in growth without the confounding effects of changes in the gonadal steroid milieu, we performed a longitudinal study in 14 young girls with idiopathic central precocious puberty during long-term pituitary-gonadal suppression. Beginning at the mean age of 2.9 yr, dehydroepiandrosterone sulfate levels, linear growth, skeletal maturation, body mass index, and secondary sexual development were evaluated at 3- to 6-month intervals for up to 12.3 yr. In 12 of the girls, levels of dehydroepiandrosterone, androstenedione, 17-hydroxypregnenolone, and 17alpha-hydroxyprogesterone were determined before and after acute ACTH stimulation every 6 months to investigate the maturation of adrenal steroidogenic enzyme activity. Serum dehydroepiandrosterone sulfate levels rose progressively throughout the study. An exponential model fit the longitudinal datasets well and indicated that dehydroepiandrosterone sulfate levels increased approximately 22%/yr from the youngest age onward. Increasing activity of 17-20 lyase (CYP17) and decreasing activity of 3beta-hydroxysteroid dehydrogenase were also evident in preadrenarchal subjects. When controlled for chronological age, no significant associations were noted between weight, body mass index, or body surface area and dehydroepiandrosterone sulfate levels. However, similar analyses revealed modest correlations of both height and growth velocity with dehydroepiandrosterone sulfate levels. Our results suggest that adrenarche is not the result of sudden rapid changes in adrenal enzyme activities or adrenal androgen concentrations; rather, adrenarche may be a gradual maturational process that begins in early childhood.

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Human puberty begins with the reemergence of GnRH secretion from its relative quiescence during childhood, activating a cascade of pituitary-gonadal maturation. This transition begins across a wide range of ages, and the rate of subsequent sexual maturation can be quite varied. The factors that regulate the hypothalamic-pituitary-gonadal axis and modulate the timing of puberty remain elusive, but it is clear that some regulation is under genetic control. Here, we discuss how new advances in genetic research may provide the tools to help unravel this long-standing mystery.

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Mutations in the GnRH receptor (GnRH-R) gene have been reported to cause idiopathic hypogonadotropic hypogonadism (IHH). Herein, we describe a 26-yr-old male with a mild phenotypic form of IHH, the fertile eunuch syndrome (IHH in the presence of normal testicular size and some degree of spermatogenesis), associated with a homozygous mutation (Gln106Arg) in the GnRH-R. This mutation, located in the first extracellular loop of the GnRH-R, has been previously shown to decrease but not eliminate GnRH binding. The proband had hypogonadal testosterone levels, detectable but apulsatile gonadotropin secretion, and a normal adult male testicular size of 17 mL at baseline. After only 4 months of treatment with hCG alone, he developed sperm in his ejaculate and his wife conceived. Following cessation of hCG therapy, the patient demonstrated reversal of his hypogonadotropism as evidenced by normal adult male testosterone levels and the appearance of pulsatile luteinizing hormone secretion. This case thus expands the emerging clinical spectrum of GnRH-R mutations, provides the first genetic basis for the fertile eunuch variant of IHH and documents the occurrence of reversible IHH in a patient with a GnRH-R mutation.

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Studies of sex steroid regulation of gonadotropin secretion in the human male have focused primarily on the respective site(s) of negative feedback of testosterone (T) and estradiol (E(2)). The use of pharmacological doses of sex steroids in these studies has precluded conclusions about the relative roles of T and E(2) in gonadotropin feedback. Thus, the aims of the present study were to 1) determine the relative contributions of T vs. E(2) to the sex steroid component of gonadotropin regulation, and 2) distinguish the feedback effects of T that that are direct (i.e. mediated by the androgen receptor) vs. indirect (mediated by aromatization to E(2)). Two experimental interventions were used: 1) inhibition of aromatization by a selective aromatase inhibitor to examine the impact of selective E(2) withdrawal; and 2) acute medical castration to examine the effect of ablating both T and E(2). Sixteen normal (NL) men (mean age, 30.5 +/- 2.2 yr) were studied. Nine NL subjects were treated with the aromatase inhibitor, anastrozole (10 mg, orally, daily, for 5 days). Twelve NL men underwent medical castration with ketoconazole (1-g loading dose followed by 400 mg, orally, four times a day for 5 days). Ketoconazole-treated subjects received concomitant treatment with dexamethasone (0.5 mg twice daily) to prevent the development of adrenal insufficiency. Single blood samples were drawn daily between 0800-1000 h. To ensure that dexamethasone was not altering the gonadotropin response to sex steroid ablation by a direct pituitary effect, five GnRH-deficient men (mean age, 37.6 +/- 3.9 yr) underwent GnRH dose-response studies at baseline and after treatment with dexamethasone (0.5 mg twice daily). Aromatase blockade caused significant lowering of E(2) (33 +/- 3 to 14 +/- 1 pg/mL; P: < 0.0005) with a corresponding increase in T levels (563 +/- 42 to 817 +/- 81 ng/dL; P: < 0.05). Treatment with ketoconazole resulted in equivalent suppression of E(2) (41 +/- 4 to 14 +/- 1 pg/mL; P: < 0.0005), but also induced castrate levels of T (491 +/- 28 to 40 +/- 3 ng/dL; P: < 0.0005). Both treatment regimens were associated with a significant increase in gonadotropin levels. For LH, the percent increase in serum levels after castration was almost 3-fold greater than that seen after selective E(2) withdrawal (275 +/- 23% with ketoconazole vs. 95.6 +/- 21% with anastrozole; P: < 0.005). Despite the divergent changes in T levels with these two maneuvers (a marked decrease after ketoconazole and a significant increase with anastrozole), the percent rise in FSH levels was similar in the two protocols (91 +/- 6% vs. 71 +/- 7%, respectively; P: = NS). Inhibin B levels were unchanged after selective E(2) withdrawal (156 +/- 23 vs. 176 +/- 19 pg/mL), but decreased slightly with ketoconazole (156 +/- 15 to 131 +/- 11 pg/mL; P: < 0.05). In contrast to the effects of glucocorticoid administration on gonadotropin secretion in women, no significant changes were observed in the GnRH-deficient men treated with dexamethasone in terms of mean LH levels (19.8 +/- 3.2 vs. 23.3 +/- 5.4 IU/L), mean LH pulse amplitude after GnRH (16.0 +/- 2.5 vs. 19.0 +/- 5.1 IU/L), or mean FSH levels (8.0 +/- 1.9 vs. 9.2 +/- 2.4 IU/L, pre vs. post). These studies provide evidence of differential regulation of gonadotropin secretion by T in the human male. T exerts both direct and indirect feedback on LH secretion, whereas its effects on FSH appear to be mediated largely by aromatization to E(2). From these data we conclude that in terms of sex steroid feedback, E(2) is the predominant regulator of FSH secretion in the human male.

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The preponderance of evidence states that, in adult men, estradiol (E2) inhibits LH secretion by decreasing pulse amplitude and responsiveness to GnRH consistent with a pituitary site of action. However, this conclusion is based on studies that employed pharmacologic doses of sex steroids, used nonselective aromatase inhibitors, and/or were performed in normal (NL) men, a model in which endogenous counterregulatory adaptations to physiologic perturbations confound interpretation of the results. In addition, studies in which estrogen antagonists were administered to NL men demonstrated an increase in LH pulse frequency, suggesting a potential additional hypothalamic site of E2 feedback. To reconcile these conflicting data, we used a selective aromatase inhibitor, anastrozole, to examine the impact of E2 suppression on the hypothalamic-pituitary axis in the male. Parallel studies of NL men and men with idiopathic hypogonadotropic hypogonadism (IHH), whose pituitary-gonadal axis had been normalized with long-term GnRH therapy, were performed to permit precise localization of the site of E2 feedback. In this so-called tandem model, a hypothalamic site of action of sex steroids can thus be inferred whenever there is a difference in the gonadotropin responses of NL and IHH men to alterations in their sex steroid milieu. A selective GnRH antagonist was also used to provide a semiquantitative estimate of endogenous GnRH secretion before and after E2 suppression. Fourteen NL men and seven IHH men were studied. In Exp 1, nine NL and seven IHH men received anastrozole (10 mg/day po x 7 days). Blood samples were drawn daily between 0800 and 1000 h in the NL men and immediately before a GnRH bolus dose in the IHH men. In Exp 2, blood was drawn (every 10 min x 12 h) from nine NL men at baseline and on day 7 of anastrozole. In a subset of five NL men, 5 microg/kg of the Nal-Glu GnRH antagonist was administered on completion of frequent blood sampling, then sampling continued every 20 min for a further 8 h. Anastrozole suppressed E2 equivalently in the NL (136 +/- 10 to 52 +/-2 pmol/L, P < 0.005) and IHH men (118 +/- 23 to 60 +/- 5 pmol/L, P < 0.005). Testosterone levels rose significantly (P < 0.005), with a mean increase of 53 +/- 6% in NL vs. 56 +/- 7% in IHH men. Despite these similar changes in sex steroids, the increase in gonadotropins was greater in NL than in IHH men (100 +/- 9 vs. 58 +/- 6% for LH, P = 0.07; and 85 +/- 6 vs. 41 +/- 4% for FSH, P < 0.002). Frequent sampling studies in the NL men demonstrated that this rise in mean LH levels, after aromatase blockade, reflected an increase in both LH pulse frequency (10.2 +/- 0.9 to 14.0 +/- 1.0 pulses/24 h, P < 0.05) and pulse amplitude (5.7 +/- 0.7 to 8.4 +/- 0.7 IU/L, P < 0.001). Percent LH inhibition after acute GnRH receptor blockade was similar at baseline and after E2 suppression (69.2 +/- 2.4 vs. 70 +/- 1.9%), suggesting that there was no change in the quantity of endogenous GnRH secreted. From these data, we conclude that in the human male, estrogen has dual sites of negative feedback, acting at the hypothalamus to decrease GnRH pulse frequency and at the pituitary to decrease responsiveness to GnRH.

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Concern has been raised that children with central precocious puberty (CPP) are prone to the development of obesity. Here we report longitudinal height, weight, and body mass index (BMI) data from 96 girls and 14 boys with CPP before, during, and after GnRH agonist (GnRHa) administration. Skinfold thickness (n = 46) and percent body fat by dual energy x-ray absorptiometry (n = 21) were determined in subsets for more accurate assessment of body composition and to validate the use of the BMI SD score as an index of body fatness in our subjects. Before the initiation of therapy (PRE), the girls with CPP had a mean BMI SD score for chronological age (CA) of 1.1+/-0.1 and for bone age (BA) of 0.1+/-0.1. By the end of the study, 12-24 months after the discontinuation of GnRHa, the mean BMI SD score was 0.9+/-0.1 for CA and 0.6+/-0.1 for BA. At the visit when GnRHa was discontinued, 41% and 22% of the girls had a BMI SD score for CA more than the 85th and 95th percentiles, respectively, indicating that obesity was present at a high rate among our subjects; the BMI SD score for CA at the PRE visit was its strongest predictor. Indeed, 86% of the girls with BMI SD score for CA above the 85th percentile when GnRHa was discontinued also had BMI SD score for CA above the 85th percentile at the PRE visit. The proportion of boys with elevated BMI SD score for CA was also high. Fifty-four percent and 31% of the SD scores were greater than the 85th and 95th percentiles after 36 months of GnRHa therapy; the BMI SD score for CA PRE had been above the 85th percentile in 71% of these overweight subjects. Obesity occurs at a high rate among children with CPP, but does not appear to be related to long term pituitary-gonadal suppression induced by GnRHa administration. Children with CPP should have a baseline BMI SD score calculated, and those at risk for obesity should be counseled appropriately.

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A small number of young girls with unsustained or slowly progressive puberty have been described, but few data regarding their final heights and adult reproductive function have been reported. We have conducted a study that delineates the initial presentation and 12-yr follow-up of 20 patients who initially presented with unsustained or slowly progressive puberty as young girls. The patients were first seen between 1984-1987. They all underwent extensive clinical and hormonal studies, including frequent blood sampling and pelvic ultrasound to characterize pituitary-gonadal function. Twelve years later, we were able to locate 17 of the patients, and 16 of these agreed to participate in a questionnaire-based follow-up study. Follow-up data about the other patients were gleaned from available medical records as were corroborative data regarding the 16 study participants. Our results indicate that this form of early puberty is a benign entity. Seventy percent of our patients experienced cessation of their early pubertal development, whereas the remainder reported a slowly progressive course. Those with a slowly progressive course were older than those with an unsustained course [mean age of the larche, 6.1 vs. 3.4 yr (P < 0.01); age of pubarche, 6.0 vs. 4.0 yr (P = 0.02); age at our evaluation, 7.1 vs. 5.2 yr (P = 0.02)]. They also had more advanced skeletal maturation (bone age, 10.2 vs. 7.3 yr; P = 0.04) at the time of our evaluation. Both groups, however, had similar outcomes with respect to linear growth and young adult reproductive function. On the average, the study patients reached their genetic targets for final height (mean final height, 165.5 +/- 2.2 cm; mean genetic target height, 164.0 +/- 1.1 cm; P = NS). The average age of menarche was 11.0 +/- 0.4 yr. Twenty-three percent of our patients have evidence of anovulatory menstrual cycles, which is comparable to the 28% found in normative studies of similarly aged women. Two of the patients have become pregnant to date. Unsustained or slowly progressive puberty in young girls does not warrant therapy with GnRH agonists. Thus, when evaluating patients with early pubertal development, one should ensure that sexual maturation is continually progressive before initiating potentially unnecessary therapy.

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Several studies have suggested that sufficient serum leptin levels may be involved in the initiation of puberty. To assess further the relationship between leptin and the onset of puberty in humans, we measured the serum leptin concentration in children with central precocious puberty (CPP). We studied 65 children with either idiopathic (IPP; n = 50 girls and 3 boys) or neurogenic central precocious puberty (NPP; n = 5 girls and 7 boys). The serum leptin levels in these patients were compared with normative data from healthy children and adolescents using SD scores that adjust for body mass index (BMI) and Tanner stage. The mean SD scores of IPP and NPP girls were +0.4 +/- 0.1 and +1.0 +/- 0.5, respectively, compared with that of age-matched prepubertal girls and +0.7 +/- 0.2 and +1.6 +/- 0.6 compared with that of girls matched for pubertal stage. The CPP girls with lower BMIs contributed larger SD scores, such that the leptin SD score was negatively correlated with BMI. A similar, modest increase in leptin levels in the CPP girls was evident when additional normative data were considered. The mean leptin SD scores of IPP and NPP boys were -0.9 +/- 0.5 and +0.7 +/- 0.3, respectively, compared with that of normal boys at Tanner stage 3-4. Serum leptin levels in the boys with CPP were not different from those in healthy boys in any of the normative studies. These data should be interpreted cautiously, but they suggest that girls with CPP have modestly elevated serum leptin concentrations compared with those in healthy children and adolescents. In addition, the negative correlation between the leptin SD score and BMI suggests that sufficient leptin levels may be associated with initiation of puberty in girls.

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Although considerable strides have been made in charting the physiology and pathophysiology of inhibin in the human, further progress awaits the development of recombinant inhibin suitable for administration in human studies. Measurements of total serum inhibin, although inadequate to chart the dynamic changes associated with normal and disordered pituitary-gonadal function, have proven to be of value as indices of ovarian tumor activity. Although the roles of specific dimeric inhibin measurements in clinical practice have not been clearly established, advances in our understanding of inhibin physiology and pathophysiology in the human suggest that inhibin B may have value as a marker of Sertoli cell function in men with infertility and as a prognostic indicator in women undergoing ovulation induction therapy.

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Serum leptin concentrations increase during childhood in both sexes. During sexual maturation, levels rise further in girls, but decrease in boys. These data suggest that testosterone either directly suppresses leptin levels or induces changes in body composition that result in lower leptin concentrations. To examine further the relationship between sex steroids and leptin, we performed a longitudinal study in children with central precocious puberty (28 girls and 12 boys) before, during, and after discontinuation of GnRH agonist-induced pituitary-gonadal suppression. Nighttime and daytime leptin levels were measured to determine whether the activity of the pituitary-gonadal axis affects their diurnal variation. In the boys, suppression of testosterone increased leptin levels, whereas resumption of puberty was associated with decreased leptin levels [3.5 +/- 0.8 vs. 9.5 +/- 3.1 ng/dL (P = 0.005) and 12.2 +/- 4.5 vs. 7.0 +/- 2.6 ng/dL (P = 0.012), respectively]. Serum leptin levels did not change in the girls with alteration of the pituitary-ovarian axis and consistently exceeded those in boys. Nighttime levels were consistently greater than daytime values by an average of 38.3% in the girls and 29.4% in the boys. These serial observations during reversible pituitary-gonadal suppression suggest that testosterone decreases leptin concentrations, but that estrogen, at least in this childhood model, has no discernible effect. In addition, our data indicate that the presence of the diurnal rhythm in leptin concentrations is independent of the state of the reproductive axis.

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BACKGROUND: Men with isolated gonadotropin-releasing hormone (GnRH) deficiency typically present with an absence of pubertal development. We describe an adult-onset form of idiopathic hypogonadotropic hypogonadism that develops after puberty. METHODS: We studied 10 men (age, 27 to 57 years) with normal sexual maturation, idiopathic infertility, sexual dysfunction, low serum testosterone concentrations, and apulsatile secretion of luteinizing hormone on frequent blood sampling. All the men had otherwise normal anterior pituitary hormone secretion and sellar anatomy. We compared the results of semen analyses and measurements of testicular volume, serum testosterone, inhibin B, and gonadotropins in these men with the results in 24 men with classic GnRH deficiency before and during GnRH-replacement therapy and in 29 normal men of similar age. RESULTS: Serum gonadotropin concentrations in the men with adult-onset GnRH deficiency were similar before and during pulsatile GnRH administration to those in the men with classic GnRH deficiency. However, as compared with men with classic GnRH deficiency, men with adult-onset hypogonadotropic hypogonadism had larger mean (+/-SD) testicular volumes (18+/-5 vs. 3+/-2 ml, P<0.001), serum testosterone concentrations (78+/-34 vs. 49+/-20 ng per deciliter [2.7+/-1.2 vs. 1.7+/-0.7 nmol per liter], P=0.004), and serum inhibin B concentrations (119+/-52 vs. 60+/-21 pg per milliliter, P<0.001). Treatment with GnRH reversed the hypogonadism and restored fertility in each of the five men who received long-term therapy. CONCLUSIONS: The recognition of adult-onset hypogonadotropic hypogonadism in men as a distinct disorder expands the spectrum of GnRH deficiency and identifies a treatable form of male infertility.

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Despite recent advances in the understanding of the pathophysiology of Kallmann's syndrome (KS), the patterns of inheritance in the majority of cases of GnRH deficiency in human subjects remain unclear. To define further the genetic and phenotypic variability of this syndrome, detailed family histories were reviewed in 106 cases of GnRH deficiency with or without anosmia [i.e. KS or idiopathic hypogonadotropic hypogonadism (IHH)]. The great majority of cases appeared to be sporadic, with only 19 probands (18%) having at least 1 family member with GnRH deficiency. However, of the families in which the proband was the sole member affected by KS or IHH, 9 had individuals with isolated anosmia, and 8 had a strong history of delayed puberty. If these phenotypes were considered as alternative manifestations of the same genetic defect that presented as KS or IHH in the proband, 34% of the cases in the present series could be considered familial. In these families, the most likely modes of transmission were assessed in several ways, including analysis of probands with KS as a distinct subset, and separate determinations based upon whether the phenotypes of isolated anosmia and/or delayed puberty were considered relevant to the inheritance of KS or IHH. The proportion of familial cases that could be attributable to an X-linked mode of inheritance was no greater than 36% in any of these analyses. We conclude that 1) most cases of GnRH deficiency in humans are sporadic and, thus, could represent new mutations; 2) the X-linked form is the least common among familial cases of KS or IHH; 3) defects in at least two autosomal genes can results in GnRH deficiency; and 4) associated clinical defects may well represent clues to the nature and/or location of these autosomal genes.

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To evaluate the physiology of inhibin B in the human male, we measured serum concentrations in normal adult men and men with isolated GnRH deficiency before and during long-term replacement with pulsatile GnRH. At baseline, inhibin B levels in the GnRH-deficient men (n = 31) were significantly lower than normal controls (85 +/- 10 pg/mL vs. 239 +/- 14 pg/mL; P < .01) and correlated positively with pretreatment testicular volume (r = .80, P = .001) and a history of spontaneous puberty, suggesting additional maturational influences on the both testicular volume and inhibin B secretion. Pulsatile GnRH administration was associated with significant increases in inhibin B, with levels averaging 108 +/- 7 pg/mL when serum LH, FSH, and T concentrations had reached the normal adult male range (n = 22; P = .02 vs. baseline). Continued GnRH administration for at least an additional year was not associated with further increases in inhibin B concentrations. Throughout the course of long-term pulsatile GnRH replacement, serum FSH levels were negatively correlated with inhibin B concentrations (e.g. r = -.71, P < 0.01; n = 14 treated 12 months after normalization of T). Although inhibin B concentrations did not correlated with sperm density during therapy, rates of fertility were higher in patients with higher baseline levels (inhibin B > or = 60 pg/mL). Increases in serum concentrations of inhibin B occurring during GnRH replacement demonstrate the gonadotropin regulation of gonadal inhibin B secretion. However, the variation in baseline inhibin B levels before GnRH administration suggests an additional gonadotropin-independent level of modulation. The negative correlation between FSH and inhibin B secretion in GnRH-deficient men receiving long-term GnRH replacement is consistent with a putative role of inhibin B in the negative feedback regulation of FSH, although direct confirmation of this role requires further investigation.

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To examine the role of inhibin B in the feedback regulation of FSH secretion in the human male, we determined serial levels in 18 men with idiopathic hypogonadotropic hypogonadism (IHH) during their initial 8 weeks of GnRH replacement. Pulsatile GnRH was administered every 2 h, with the dose increased at 2-week intervals (5-50 ng/kg/bolus). Every 2 weeks, sera were assayed for inhibin B, FSH, LH, and testosterone. Serial comparisons were performed within the IHH group as well as vs. normal men (n = 20). The baseline inhibin B level in IHH patients averaged 68 +/- 11 pg/mL (mean +/- SEM), significantly less than that in normal men (239 +/- 14 pg/mL; P < 0.001). After 8 weeks of pulsatile GnRH, inhibin B levels in the IHH patients increased significantly to 118 +/- 14 pg/mL (P = 0.003). During GnRH replacement, FSH concentrations correlated negatively with inhibin B concentrations at all doses. Patients previously treated with testosterone began with somewhat lower inhibin B levels but demonstrated a significantly greater increase in serum concentrations than patients who had received prior gonadotropin or GnRH therapy. A history of cryptorchidism did not have a significant impact on inhibin B concentrations before or during GnRH replacement. The low inhibin B levels in IHH men at baseline and their prompt increase in response to pulsatile GnRH suggest acute regulation by gonadotropin stimulation of the testis. The variation in inhibin B levels at baseline and in response to GnRH suggest that prior gonadotropin exposure and seminiferous tubular development also modulate inhibin B secretion. The consistent negative correlation between FSH and inhibin B during the induction of sexual maturation with GnRH supports the role of gonadal inhibin B secretion as an important endocrine regulator of FSH in the human male.

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GnRH pulse frequency, amplitude, and interpulse interval have all been demonstrated to regulate gonadotropin secretion individually. We tested the hypothesis that the contour of the GnRH pulse also modulates gonadotropin output in 10 men with isolated GnRH deficiency in whom a fixed GnRH dose was administered at a constant physiologic frequency by either instantaneous bolus or by 1-, 5-, or 30-min infusions. LH, FSH and free alpha subunit (FAS) responses were also compared to spontaneous gonadotropin secretion in normal adult men. While the LH and FAS pulses following the instantaneous bolus and 1-min infusion of GnRH were indistinguishable, further increases in the duration of gonadotrope stimulation by GnRH were associated with progressive decreases in all parameters of gonadotropin secretion (mean levels, amplitude, peak levels, AUC). FSH secretion was also decreased following variations in the contour of the GnRH pulse, although overall changes were less dramatic than for LH and FAS. The LH pulses following the bolus GnRH stimulation were indistinguishable from spontaneous LH pulses occurring in normal men whereas those stimulated by the 1-, 5-, and 30-min infusions of GnRH became progressively blunted with the lowest levels of secretion occurring after the longest infusion. In sharp contrast, FAS pulse parameters in the GnRH-deficient subjects greatly exceeded those of normal men regardless of the contour of the GnRH stimulus, whereas mean FSH levels were all modestly (although significantly) higher than those of normal adult men. These results demonstrate that the pituitary is sensitive to subtle changes in the contour of the GnRH stimulus, with a more prolonged duration of GnRH stimulation resulting in a diminished pituitary response. Alterations of the contour of endogenous GnRH secretion may represent an additional mechanism for altering gonadotrope function and provide additional evidence for the differential regulation of LH, FAS, and FSH by GnRH. However, the previously reported elevated levels of FAS secretion in GnRH-deficient men undergoing long-term GnRH replacement are not explained by abnormalities of GnRH contour.

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During long term replacement with a GnRH regimen that restores their gonadotropin and sex steroid levels to normal, men with idiopathic hypogonadotropic hypogonadism (IHH) exhibit excessive secretion of pituitary free alpha-subunit (FAS). To characterize further the dose and duration of exogenous GnRH required to elicit this response, FAS, LH, FSH, and testosterone were determined during the first 8 weeks of GnRH administration in 10 men with IHH. The GnRH dose was increased stepwise every 2 weeks from 5 to 100 ng/kg every 2 h. Hormonal responses were compared with normative data for both pubertal boys and adult men. Low baseline levels of LH (mean +/- SEM, 0.9 +/- 0.03 IU/L), FSH (2.5 +/- 0.4 IU/L), FAS (148 +/- 21 ng/L), and testosterone (2.5 +/- 0.3 nmol/L) increased progressively after GnRH replacement. Mean FAS levels and pulse amplitudes significantly exceeded those in normal adult men by 4-6 weeks when their LH responses to GnRH administration remained below adult norms. By week 8 (50 ng GnRH/kg every 2 h), mean levels of LH, FSH, and FAS (13.7 +/- 2.1 IU/L, 15.4 +/- 4.0 IU/L, 627 +/- 75 ng/L, respectively) significantly exceeded adult male concentrations (P < 0.03). However, mean LH and FSH concentrations were not significantly different from midpubertal controls, in whom FAS levels were comparable to those in normal adults, verifying the excessive nature of FAS secretion relative to intact gonadotropins in the IHH patients. As this imbalance between FAS and dimeric gonadotropin secretion was established early in the current study when low doses of GnRH presumably resulted in low levels of receptor occupancy in vivo, it does not appear to result from partial pituitary desensitization induced by pharmacological GnRH stimulation. Rather, it appears to represent an inherent property of the GnRH-deficient state that is unmasked when GnRH input to the pituitary is restored. Further work will be necessary to elucidate the mechanism of this apparent defect in FAS regulation in GnRH-deficient men.

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Gonadotropin-independent precocity (GIP) is a syndrome marked by precocious pubertal development in the absence of pubertal levels of gonadotropins. To investigate the discrete patterns of central nervous system, gonadal, adrenal, and skeletal maturation in this syndrome, we conducted longitudinal studies spanning up to 10 yr in two such affected individuals. A cross-sectional analysis of adrenal androgen secretion was performed in nine additional patients to assess further the time course of adrenarche in GIP. Serial evaluations revealed progression of secondary sexual characteristics, statural growth, and skeletal maturation, all consistent with ongoing exposure to pubertal gonadal steroid levels. On the other hand, adrenarche (n = 11) and spontaneous and GnRH-stimulated gonadotropin secretion (n = 2) progressed in chronological age-appropriate manners despite long term pubertal levels of gonadal sex steroid secretion. After the development of central puberty, as documented by the appearance of pulsatile gonadotropin secretion, we sought to determine whether the potential for gonadal autonomy persisted. Despite complete pituitary desensitization induced by administration of a GnRH agonist, both patients studied demonstrated an ongoing capacity to secrete pubertal levels of gonadal steroids. Our study suggests that the timing of adrenarche and central puberty in these subjects with GIP was apparently unaltered by prolonged exposure to gonadal steroids. Subsequent to the development of central puberty, pulsatile gonadotropin secretion may override and, thus, mask the underlying defect(s) in adolescents and adults with histories of GIP.

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Chronic GmRH agonist (GnRHa) administration has been shown to suppress pituitary-gonadal function in children with central precocious puberty (CPP), but long term data after the reactivation of gonadarche posttherapy are not yet available. This study evaluated the menstrual function of 46 girls with CPP who had been treated for at least 2 yr with GnRHa (deslorelin or histrelin, sc, daily) and were up to 7 yr posttreatment, including 21 postmenarcheal girls who collected weekly overnight urine samples for 12 consecutive weeks to assess rates of ovulation by urinary pregnanediol-3 beta-glucuronide measurements. Menarche occurred at age 12.1 +/- 1.0 yr (mean +/- SD), on the average 1.2 +/- 0.8 yr posttherapy (range, 0.1-4.3 yr). Menstrual cycle lengths became increasingly regular, with cycles of 25- to 35-day duration reported by 41% of the girls in the first year postmenarche and 65% of the girls studied 3 or more years postmenarche. Ovulation was demonstrated in 50% of the girls studied within 1 yr of menarche and in 90% of the girls studied 2 yr or more postmenarche, including 5 girls who reported pregnancies. The development of regular ovulatory menstrual function in these girls with CPP is in accord with previously documented patterns in normal adolescents. While these data provide further evidence supporting the safety of long term GnRHa therapy, continued studies will be necessary to characterize fully the reproductive function in CPP patients through adolescence and adulthood.

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