Serum inhibin concentrations before and during gonadotropin treatment in men with hypogonadotropic hypogonadism: physiological and clinical implications

Gonadotropins for pubertal induction in males with hypogonadotropic hypogonadism: systematic review and meta-analysis

OBJECTIVE

Hypogonadotropic hypogonadism is characterized by inadequate secretion of pituitary gonadotropins, leading to absent, partial, or arrested puberty. In males, classical treatment with testosterone promotes virilization but not testicular growth or spermatogenesis. To quantify treatment practices and efficacy, we systematically reviewed all studies investigating gonadotropins for the achievement of pubertal outcomes in males with hypogonadotropic hypogonadism.

DESIGN

Systematic review and meta-analysis.

METHODS

A systematic review of Medline, Embase, Global Health, and PsycINFO databases in December 2022. Risk of Bias 2.0/Risk Of Bias In Non-randomized Studies of Interventions/National Heart, Lung, and Blood Institute tools for quality appraisal. Protocol registered on PROSPERO (CRD42022381713).

RESULTS

After screening 3925 abstracts, 103 studies were identified including 5328 patients from 21 countries. The average age of participants was <25 years in 45.6% (n = 47) of studies. Studies utilized human chorionic gonadotropin (hCG) (n = 93, 90.3% of studies), human menopausal gonadotropin (n = 42, 40.8%), follicle-stimulating hormone (FSH) (n = 37, 35.9%), and gonadotropin-releasing hormone (28.2% n = 29). The median reported duration of treatment/follow-up was 18 months (interquartile range 10.5-24 months). Gonadotropins induced significant increases in testicular volume, penile size, and testosterone in over 98% of analyses. Spermatogenesis rates were higher with hCG + FSH (86%, 95% confidence interval [CI] 82%-91%) as compared with hCG alone (40%, 95% CI 25%-56%). However, study heterogeneity and treatment variability were high.

CONCLUSIONS

This systematic review provides convincing evidence of the efficacy of gonadotropins for pubertal induction. However, there remains substantial heterogeneity in treatment choice, dose, duration, and outcomes assessed. Formal guidelines and randomized studies are needed.

Semen quality in patients with pituitary disease and adult-onset hypogonadotropic hypogonadism

OBJECTIVE

Gonadotropins (luteinizing hormone (LH) and follicle-stimulating hormone (FSH)) are released from the pituitary gland and stimulate Leydig cells to produce testosterone and initiates spermatogenesis. Little is known about how and when the deterioration of semen quality occurs in patients with adult-onset gonadotropin insufficiency.

DESIGN AND METHODS

A retrospective study comprising 20 testosterone-deficient men (median age, 29 years) with acquired pituitary disease who delivered semen for cryopreservation before initiation of testosterone therapy. Semen variables and hormone concentrations were compared to those of young healthy men (n = 340).

RESULTS

Thirteen of 20 patients (65%) and 82% of controls had total sperm counts above 39 million and progressive motile spermatozoa above 32% (P = 0.05). For the individual semen variables, there were no significant differences in semen volume (median (intraquartile range) 3.0 (1.3-6.8) vs 3.2 (2.3-4.3) mL, P = 0.47), sperm concentration 41 (11-71) vs 43 (22-73) mill/mL (P = 0.56) or total sperm counts (P = 0.66). One patient had azoospermia. Patients vs controls had lower serum testosterone 5.4 (2.2-7.6) vs 19.7 (15.5-24.5) nmol/L (P = 0.001), calculated free testosterone (cfT) 145 (56-183) vs 464 (359-574) pmol/L (P < 0.001), LH 1.5 (1.1-2.1) vs 3.1 (2.3-4.0) U/L (P = 0.002) and inhibin b (P < 0.001). Levels of FSH were similar (P = 0.63). Testosterone/LH ratio and cfT/LH ratio were reduced in patients (both P < 0.001).

CONCLUSIONS

Despite Leydig cell insufficiency in patients with acquired pituitary insufficiency, the majority presented with normal semen quality based on the determination of the number of progressively motile spermatozoa. In addition, the data suggest reduced LH bioactivity in patients with pituitary insufficiency.

Inhibin

Inhibin is a glycoprotein hormone, consisting of two dissimilar, disulphide-linked subunits, termed α (MW 20kD) and β (MW 3-15kD), which inhibits the production and/or secretion of pituitary gonadotrophins, preferentially follicle stimulating hormone (FSH). The most widely studied inhibin molecule has a molecular weight of 31-32kD, as purified and cloned from bovine, porcine, ovine, rat and human sources. Higher molecular weight forms have been identified in ovarian follicular fluids and in culture media of granulosa and Sertoli cells, and generally differ from the 31kD form in having larger α-subunits, designated by their molecular weights, e.g. α44 in 58kD inhibin. There are two forms of the β-subunit, named βA and βB and the corresponding inhibin dimers have been named inhibin A and inhibin B. Dimers of the β-subunit, which have been shown to have FSH stimulating activity, are termed activins and are designated activin A, B or AB depending on whether the dimer is a homodimer of βA or βB or a heterodimer of βA and βB (Figure 1). The major gonadal source of inhibin is the granulosa cell in the female and the Sertoli cell in the male. Other potential cellular sites of origin will be discussed below.

Early assessment of hypothalamic-pituitary-gonadal function in patients with congenital hypothyroidism of central origin

CONTEXT

Early recognition of gonadotropic dysfunction could enable well-timed growth and maturation and prevent damage to gonads and external genitalia. The adaptation of the Dutch neonatal screening program for congenital hypothyroidism in the mid 1990s resulted in enhanced detection of congenital hypothyroidism of central origin (CH-C), with high likelihood of multiple pituitary hormone deficiency, including gonadotropin (Gn) deficiency.

OBJECTIVE

We analyzed GnRH test results and baseline Gn and sex hormone measurements in 15 infants with CH-C to examine these diagnostic tools for assessment of the integrity of the hypothalamus-pituitary-gonad axis in young infants.

DESIGN

In a nationwide prospective study (1994-1996), patients were referred to our department if neonatal CH screening results were indicative of CH-C. When CH-C was confirmed, GnRH tests and baseline Gn and sex hormone measurements took place at the age of 3 months, when euthyroid status had been accomplished by T4 supplementation, and if necessary, cortisol supplementation was installed.

SETTING

The study took place at the Department of Pediatric Endocrinology, Emma Children's Hospital, Academic Medical Center, University of Amsterdam (referral center).

PATIENTS

The study included 15 neonates (five girls and 10 boys) with CH-C, detected by neonatal screening, in whom investigation of the hypothalamus-pituitary-gonad axis could be performed at 3 months of age.

MAIN OUTCOME MEASURES

Results of GnRH tests and baseline Gn and sex hormone measurements were assessed.

RESULTS

GnRH tests at 3 months of age showed a pattern indicative of endogenous GnRH stimulation in nine infants and a blunted response in six. Baseline Gn and sex hormone concentrations except estradiol (P = 0.053) were significantly different between responders and nonresponders.

CONCLUSIONS

The GnRH test and baseline measurements of Gn and sex hormone serum concentrations at 3 months of age are promising options in the assessment of hypothalamic-pituitary-gonadal function in infants with CH-C of both sexes.

Hormonal control of inhibin B in men

Serum inhibin B (IB) and testosterone (T) levels, secreted by Sertoli cells (SC) and Leydig cells (LC), respectively, are parameters of the functional state of these cells. Whereas LC activity and, consequently, T secretion are regulated by serum LH, factors regulating IB secretion by SC are still partially unknown. There is evidence that under certain conditions such as puberty, aging or some spermatogenesis defects, LH levels or Gn-independent factors might contribute to regulating SC activity and IB secretion. Among these factors, GH and IGF-I as well as PRL might have a role. Therefore, in order to explore the possible effects of either LH alone and FSH alone or a combination of both Gn, respectively, on SC function, IB plasma levels and spermatogenesis, we studied their effects in 6 patients with hypogonadotropic hypogonadism (HH), whereas the effects of GH on these parameters were studied in 6 men with panhypopituitarism (PH). Finally, the possible effects of PRL on SC function and spermatogenesis were studied in 6 patients with hyperprolactinemia (HPRL); 24 normal, fertile adults served as control group. In men with HH, neither human chorionic Gn (hCG) nor FSH, respectively, were able to increase serum IB after 3 months of therapy, whereas combined Gn therapy for 24 months increased IB plasma levels and stimulated spermatogenesis in 4 out of 6 hypogonadal men. In panhypopituitaric men, GH added to the classical Gn therapy did not have an additional effect on serum IB levels or spermatogenesis. Surprisingly, in our hyperprolactemic men, IB plasma levels were increased and positively correlated (p<0.01) with serum PRL levels, whereas normalization of the latter by cabergoline treatment caused a decrease of IB levels and a moderate increase in T, LH and FSH. In conclusion, the lack of SC response to FSH therapy alone, as opposed to the response to combined Gn therapy, might indicate that normalization of serum T by hCG is required to obtain IB secretion by SC. Addition of GH did not affect SC function, serum IB levels or spermatogenesis. Finally, our data suggest that PRL plasma levels might have a direct role on IB secretion, suggesting that the hypogonadism found in patients with HPRL might be a consequence of both central (inhibition of Gn secretion) and peripheral (stimulation of IB secretion) origin.

Induction of spermatogenesis in idiopathic hypogonadotropic hypogonadism with gonadotropins in older men

We investigated the treatment results in 6 azoospermic idiopathic hypogonadotropic hypogonadism (IHH) cases that remained untreated 41-47 years of age. Medical history, physical examination, hormone profile measurements, peripheral blood karyotype, skull X-ray and/or magnetic resonance imaging were performed. Patients received 1,000 to 5,000 IU hCG, 2-3 times per week, and 75 to 150 IU hMG, 2-3 times per week for 24 months. Serum testosterone levels were assessed every month for maximum 6 months to evaluate optimal dose of treatment and then every 3 months thereafter. Sperm counts were assessed every 3 months. Testosterone level increased from 2.7 +/- 0.9 mIU/L to 22 +/- 7.04 mIU/L with treatment; testicular volume increased by 4.6 ml during the treatment. Sperm were detected in the ejaculate in 3 out of 6 patients on the 22nd, 18th, and 15th month of treatment. 3 patients underwent testicular biopsy; histopathology revealed tubular hyalinization. Spermatogenesis in older men with IHH was restored by exogenous gonadotropins.

Sperm retrieval in infertile males: comparison between testicular sperm extraction and testicular sperm aspiration techniques

Improvements in using retrieved testicular spermatozoa in infertile males to achieve fertilization and pregnancy has enabled patients with clinical azoospermia and non-obstructive testicular failure to father children. In this review article, we compare the relative yields of the two major techniques for sperm retrieval in males with non-obstructive azoospermia; TESE (Testicular Sperm Extraction) and TESA (Testicular Sperm Aspiration). We also discuss the role of follicle-stimulating hormone (FSH), testicular volume, serum levels of inhibin B, testicular doppler flow pattern, chromosome Yq deletions, and presence of spermatids in azoospermic ejaculates as predictors of presence or absence of spermatozoa in biopsied testicular tissues. In conclusion, although most studies favor the more invasive TESE in terms of sperm retrieval success rate, the degree of certainty in this regard remains unsatisfactory, and future studies need to address the issues of standard error and differential misclassification attributable to needle gauge size in patients undergoing TESA.

Seasonal changes in spermatogenic activity and in plasma levels of FSH, LH and testosterone, and the effect of immunization against inhibin in the male silver fox (Vulpes vulpes)

The cellular composition of the silver fox testis assessed by DNA flow cytometry and histological analysis exhibited marked circannual alterations. The proportion of haploid cells increased from late October to the breeding season in February, while that of diploid cells decreased and that of tetraploid cells fluctuated during the same period. Towards the end of March these changes were reversed. The seasonal variations in testicular histology paralleled the changes in distribution of cells from the different DNA populations. In August, 69% of the tubules contained spermatogonia as the only type of germ cell, while the remaining 31% also contained a few primary spermatocytes. In late October more than 50% of the tubules contained spermatocytes, and during the period of further activation from early December-February the seminiferous epithelium included round and/or elongated spermatids as well. In February, all tubules contained complete associations of germ cells, whereas in late March tubules with spermatogonia only and spermatogonia together with a few spermatocytes reappeared. In May, only such tubules could be found indicating total regression. Plasma concentrations of FSH and LH increased from early November, both gonadotrophins reaching maximum levels in December or early January, and then both declined during the second part of January, immediately prior to the actual breeding season. LH values showed a few smaller peaks in the beginning of June, whereas FSH levels were generally low until the next period of testicular reactivation. Testosterone concentrations were also low during most of the year but rose in November and December to reach a peak in January and a second peak in June. In animals immunized against inhibin the distribution of haploid, diploid and tetraploid cells did not deviate to any great extent from that in the controls, except in March when the immunized males had a markedly lower proportion of tetraploid cells, and in May, when they had a distinctly higher proportion of haploid cells. These findings were partly reflected by the histology. In the immunized animals, plasma FSH levels started to increase at approximately the same time but peaked higher and remained elevated almost 1 month longer than in the controls, whereas both the rise and decline in LH levels generally coincided with the variations in these animals, but the values were mostly higher. The testosterone profiles were similar to those in the controls except that the maximum values were also usually higher.

Differential patterns of inhibin secretion in response to gonadotrophin stimulation in normal men

Inhibin B is produced by the testis, and its constituent alpha and beta B subunits have been localized immunohistochemically to Leydig as well as Sertoli cells in both rodent and human testes. Whether Leydig cells contribute to circulating inhibin B concentrations, however, is uncertain. We have investigated this by selectively stimulating Leydig and Sertoli cells with hCG and FSH, respectively. The study was a randomized crossover trial, investigating responses to 225 IU recombinant FSH or 3000 IU hCG administered s/c 4-6 weeks apart. Ten normal men were recruited to participate. Blood was taken twice before treatment and after 8, 24, 48, 72 and 96 h. Serum was assayed for FSH, LH and testosterone by radioimmunoassay (RIA); inhibin B and pro-alpha C inhibin forms by ELISA. Administration of hCG, but not FSH, caused a rapid increase in blood testosterone levels, which reached a maximum after 72 h (22.2 +/- 2.7-50.1 +/- 4.5 nmol/L, p < 0.001). Inhibin B concentrations in blood were unchanged following either treatment. Conversely, pro-alpha C concentrations increased following both treatments. FSH administration resulted in a gradual increase in pro-alpha C concentrations (369 +/- 18 pg/mL pre-treatment to 453 +/- 33 pg/mL after 96 h, p=0.013). Administration of hCG resulted in a more rapid response, with pro-alpha C concentrations rising from 384 +/- 23 pg/mL pre-treatment to a peak at 48 h of 535 +/- 45 pg/mL (p=0.007). This response was more rapid than that of testosterone. These results demonstrate that adult human Leydig, as well as Sertoli, cells secrete inhibin alpha subunit in response to gonadotrophin stimulation but provide no evidence for the secretion of inhibin B from Leydig cells. The lack of change in inhibin B secretion in response to FSH suggests that more prolonged or intense stimulation of Sertoli cells may be required for secretion of the dimeric form.

Regulation of inhibin production in the human male and its clinical applications

Investigation of the regulation of testicular function has been enhanced by the ability to measure the dimeric, biologically active form of inhibin in men, inhibin B. This has allowed the demonstration that inhibin B is the afferent arm of the feedback loop from the testis that regulates FSH secretion, and investigation of inhibin B levels during reproductive development and in a variety of physiological and pathological states. Such studies have demonstrated many primary aspects of the relationship between FSH, testicular function (and in particular spermatogenesis) and inhibin B levels in blood, though many more specific questions remain. These include the precise nature of the relationship between inhibin B secretion and Sertoli cell function and how this relationship is influenced by the germ cell types present in the testis and by overall sperm production. When such information becomes available it will allow more accurate interpretation of blood concentrations of inhibin B. Similarly, apical secretion of inhibin B into seminal plasma may have considerable value in aiding assessment of the status of the seminiferous epithelium. Finally, neonatal secretion of inhibin B as a measure of Sertoli cell number and/or as a predictor of adult reproductive function offers novel possibilities for assessment and intervention.

Inverse relationship between serum inhibin B and FSH levels in prepubertal boys with cryptorchidism

To investigate the gonadal control of FSH secretion in prepuberty, we studied the relationship between circulating inhibin B and FSH levels in 16 prepubertal boys with cryptorchidism (age range, 1-8 y). The effect of Leydig cell stimulation on the secretion of inhibin B, sex steroids, and FSH was investigated in nine boys who were given human chorionic gonadotropin (hCG) treatment. In these boys, serum inhibin B, testosterone, estradiol, and gonadotropin levels were measured before and on the fourth day of the last (third) hCG injection, given at 1-wk intervals. Except for one boy with both high inhibin B and FSH concentrations, basal serum levels of these hormones correlated negatively (r(s) = -0.79, n = 15, p < 0.005). This inverse relationship remained significant in the subgroup of boys younger than 2 y of age (r(s) = -0.84, n = 11, p = 0.008) who also had greater variance of serum FSH concentrations than 14 control boys of similar age with normally located testes (p < 0.01). hCG stimulation increased serum testosterone and suppressed serum FSH concentrations in each boy (n = 9, p < 0.005). In the four oldest subjects, the serum inhibin B level increased from the mean of 91 to 135 pg/mL (p < 0.05). These findings suggest that inhibin B regulates FSH secretion in early childhood. Moreover, the hCG-induced suppression of FSH secretion was probably mediated by sex steroids rather than by inhibin B. Finally, the increase in serum inhibin B concentration during the hCG treatment was likely to be indirect via Leydig cell-Sertoli cell or Sertoli cell-germ cell interaction(s).

Serum inhibin levels before and after gonadotropin stimulation in cryptorchid boys under age 4 years

We evaluated eleven cryptorchid boys under four years of age to determine the usefulness of serum inhibin as a marker of seminiferous tubule dysfunction. Serum testosterone, inhibin, LH and FSH concentrations were measured by RIA before and after 6 weeks of human chorionic gonadotropin plus human menopausal gonadotropin therapy, and bilateral testicular biopsies were performed at orchiopexy. Hormonal results from the cryptorchid group were compared to those from an age-matched control group. Basal LH and testosterone levels were similar in the two groups. Cryptorchid boys had lower basal inhibin and higher FSH levels than controls. After gonadotropin treatment the inhibin/FSH ratio was lower in cryptorchid than control children, suggesting the presence of seminiferous tubule damage (p = 0.002). Normal numbers of spermatogonia were seen in 6/9 scrotal and in 1/13 cryptorchid testes. The peak of inhibin was positively correlated to the number of spermatogonia (r = 0.68; p = 0.02). We conclude that basal and stimulated inhibin concentrations, as well as basal and stimulated inhibin/FSH ratio, provide additional information on seminiferous tubule function in cryptorchid boys and can be useful to evaluate Sertoli cell function in these patients.

Longitudinal reproductive hormone profiles in infants: peak of inhibin B levels in infant boys exceeds levels in adult men

The gonads are usually considered quiescent organs in infancy and childhood. However, during the first few postnatal months of life, levels of gonadotropins and sex hormones are elevated in humans. Recent epidemiological evidence suggests that environmental factors operating perinatally may influence male reproductive health in adulthood. The early postnatal activity of the Sertoli cell, a testicular cell type that is supposed to play a major role in sperm production in adulthood is largely unknown. Recently, the peptide hormone inhibin B was shown to be a marker of Sertoli cell function in the adult male. In the adult woman, inhibin B is secreted by the granulosa cells. Longitudinal serum levels of inhibin B were measured in healthy boys (n = 15) and girls (n = 15), in cord blood, and every third month during the first 2 yr of life. In addition, serum levels of FSH, LH, and testosterone (boys) were measured in the same group of children. In boys, inhibin B, FSH, LH, and testosterone levels were all elevated at 3 months of age. However, the peak of inhibin B was unexpectedly high, into the supraadult range (mean +/- SE, 378 +/- 23 pg/mL) and persisted much longer than the elevation of FSH, LH, and testosterone. Thus, although levels of FSH, LH, and testosterone decreased into the range observed later in childhood by the age of 6-9 months, serum inhibin B levels remained elevated up to at least the age of 15 months. In girls, the hormonal pattern was generally more complex, with a high interindividual variation in levels of inhibin B, FSH, and LH within each age. In conclusion, the sustained elevation of inhibin B to supraadult levels in infant boys indicates that the neonatal period may be a developmental window important for Sertoli cell proliferation and maturation. Thus, the gonads may be potentially vulnerable to exogenous endocrine interference, e.g. from environmental factors during this period of life. Measurement of serum levels of inhibin B in infants may give clinical clues about developmental deficiencies in the gonads that otherwise only become apparent around puberty or later in life.

Serum inhibin B in healthy pubertal and adolescent boys: relation to age, stage of puberty, and follicle-stimulating hormone, luteinizing hormone, testosterone, and estradiol levels

Inhibin B levels were measured in serum from 400 healthy Danish prepubertal, pubertal, and adolescent males, aged 6-20 yr, in a cross-sectional study using a recently developed immunoassay that is specific for inhibin B, the physiologically important inhibin form in men. In addition, serum levels of FSH, LH, testosterone, and estradiol levels were measured. Serum levels of inhibin B, FSH, LH, testosterone, and estradiol all increased significantly between stages I and II of puberty. From stage II of puberty the inhibin B level was relatively constant, whereas the FSH level continued to increase between stages II and III. From stage III of puberty the FSH level was also relatively constant, although there was a nonsignificant trend of slightly decreased FSH levels at pubertal stage V compared to stage IV. The levels of serum LH, testosterone, and estradiol increased progressively throughout puberty. In prepubertal boys younger than 9 yr, there were no correlation between inhibin B and the other three hormones. In prepubertal boys older than 9 yr, a significant positive correlation was observed between inhibin B and FSH, LH, and testosterone. However, at this pubertal stage, each hormone correlated strongly with age, and when the effect of age was taken into account, only the partial correlation between inhibin B and LH/testosterone remained statistically significant. At stage II of puberty, the positive partial correlation between inhibin B and LH/testosterone was still present. At stage III of puberty, an negative partial correlation between inhibin B and FSH, LH, and estradiol was present, whereas no correlation between inhibin B and testosterone could be observed from stage III onward. The negative correlation between inhibin B and FSH persisted from stage III of puberty onward, whereas the correlation between inhibin B and LH and between inhibin B and estradiol was nonsignificant at stages IV and V of puberty. In conclusion, in boys, serum inhibin B levels increase early in puberty; by pubertal stage II the adult level of inhibin B has been reached. The correlation of inhibin B to FSH, LH, and testosterone changes during pubertal development. Early puberty is characterized by a positive correlation between inhibin B and LH/testosterone, but no correlation to FSH. Late puberty (from stage III) is characterized by a negative correlation between inhibin B and FSH (which is maintained in adult men), a diminishing negative correlation between inhibin B and LH, and no correlation between inhibin B and testosterone, suggesting that developmental and maturational processes in the hypothalamic-pituitary-gonadal axis take place, leading to the establishment of the closed loop feedback regulation system operating in adult men. The positive correlation between inhibin B and LH/ testosterone at the time when serum inhibin B levels rise early in puberty suggests that Leydig cell factors may play an important role in the maturation and stimulation of Sertoli cells in the beginning of pubertal development.

Inhibin and steroid response to testicular stimulation with pure FSH (Metrodin) in infertile men with unilateral cryptorchidism

Static measurements of immunoreactive inhibin have proven of little relevance in the diagnosis of testicular disorders. Dynamic evaluation of the inhibin secretory reserve might detect a specific Sertoli cell defect in a subgroup of infertile men. We compared the response of inhibin and steroids to an intravenous injection of pure FSH (Metrodin, Serono, 300 IU) in 13 infertile men with unilateral cryptorchidism to that in eight normal fertile men. Blood was aspirated before, 24, 48, and 72 h after the FSH injection. Two subgroups of patients with unilateral cryptorchidism were detected: those who responded by secreting inhibin in a pattern similar to normal men (seven patients), and those who responded poorly or not at all (six patients). The presumed cause of this difference is a defect of Sertoli cell reserve function due to a combination of insults to the testes, and not to cryptorchidism itself. The difference in response to FSH cannot be predicted from semen analysis nor from static hormone measurements. Overall, inhibin levels correlated significantly with the serum concentrations of FSH (r = -0.36, P < 0.05), testosterone (r = 0.37, P < 0.05), and 17-hydroxyprogesterone (r = 0.66, P < 0.001). It is concluded that, in infertile men with unilateral cryptorchidism, Stimulation of Sertoli cells by FSH can identify a subgroup of patients with Sertoli cell malfunction involving inhibin synthesis.

Testicular secretion after pulsatile human menopausal gonadotropin therapy in gonadotropin-releasing hormone agonist desensitized dysspermic men

OBJECTIVE

To evaluate Leydig and Sertoli cell response to prolonged pulsatile stimulation with hMG after pituitary desensitization with the GnRH agonist (GnRH-a) triptoreline in normogonadotropic men with abnormal semen analyses.

DESIGN

A group of four oligozoospermic men were investigated in the following manner: [1] basal and GnRH-hCG stimulated activity were assessed in all volunteers; [2] a long-acting form of the GnRH-a triptoreline (3.75 mg every month for 3 months) was given, and its effectiveness was evaluated on day 20; and [3] on that day hMG pulsatile administration was introduced (150 IU per 24 hours in 90-minute pulses) with serial hourly sampling (6 to 7 hours) for measurement of FSH, LH, T, E2, and inhibin on days 20, 41, and 90 from the first GnRH-a injection.

RESULTS

Initial evaluation showed normal basal, GnRH, and hCG-stimulated hormone concentrations. Pituitary and gonadal activity were effectively suppressed by GnRH-a when tested on day 20. Pulsatile hMG had no immediate stimulatory effect on gonadal activity (day 20). However, on middle and final evaluations (days 41 and 90), basal T, E2, and inhibin had risen to pre-GnRH-a levels, and, moreover, distinct secretory pulses were seen for these hormones.

CONCLUSION

These findings indicate that suppression of pituitary gonadotropin activity with triptoreline combined with pulsatile hMG stimulation offers a new, useful tool for investigation of the male reproductive system in oligozoospermic men.

Inhibin and follicle-stimulating hormone levels in gonadotroph adenomas: evidence of a positive correlation with tumour volume in men

OBJECTIVE

Gonadotroph adenomas are generally revealed by symptoms of mass effect at the stage of macroadenoma. Most of them hypersecrete FSH and/or gonadotrophin subunits. Rarely they hypersecrete LH, which could induce endocrinological symptoms. As the glycoprotein inhibin is secreted by the gonads under FSH control, we have evaluated whether high immunoreactive inhibin (iINH) levels correlated with FSH hypersecretion and whether iINH and FSH levels were related to tumour volume in subjects with gonadotroph adenomas.

PATIENTS

Forty-five patients (30 men, 15 women) were retrospectively selected on the basis of immunostaining technique using specific antibodies raised against FSH-beta, LH-beta and glycoprotein alpha-subunit.

MEASUREMENTS

Immunoreactive inhibin (iINH) was measured by radioimmunoassay using antiserum 1989 raised to bovine inhibin. Tumour volume index was the product in cm3 of length, width and height of the adenoma as assessed by computerized tomography.

RESULTS

In men (age 21-61 years), iINH levels were positively correlated with FSH levels (Spearman's r = 0.67, P < 0.001), and both iINH and FSH levels were significantly correlated with tumour volume index (Spearman's r = 0.38, P < 0.05 and r = 0.39, P < 0.05 respectively). In the subgroup of men with normal FSH levels (n = 17), the correlation of FSH with tumour volume index was high: Spearman's r = 0.56, P < 0.05. In the post-menopausal women (n = 8, age > 55 years), iINH levels were undetectable or below the follicular phase range regardless of FSH values. In the premenopausal women (n = 7, age 22-49 years, follicular phase or amenorrhoea) iINH levels were above follicular phase range in three women including one who had very high FSH levels.

CONCLUSIONS

These data show that in men with gonadotroph adenoma FSH levels are related to tumour mass and suggest that a significant part of circulating FSH in patients with normal FSH levels arises from the tumour. The significant correlation between iINH and FSH levels demonstrates that tumoral FSH is bioactive and that high iINH levels do not exert any feedback control on tumoral FSH secretion. Therefore the coexistence of high FSH levels with high iINH levels is strongly suggestive of a gonadotroph adenoma. Gonadotroph adenomas seem to represent a unique model of long-term FSH stimulation of inhibin-producing cells, in some way analogous to that created by repetitive administration of exogenous FSH.