Biphasic increase in serum inhibin B during puberty: a longitudinal study of healthy Finnish boys

Puberty and Inhibin B in 35 Adolescents With Pituitary Stalk Interruption Syndrome

Background: In patients with pituitary stalk interruption syndrome (PSIS), long-term follow-up is necessary to address their gonadotrophic status. The objectives of this study were (1) to describe pubertal features of and (2) to assess the ability of serum inhibin B concentration to predict hypogonadotropic hypogonadism (HH) in patients with PSIS. Methods: This retrospective single-center study included 35 patients with PSIS and known gonadotrophic status for whom a serum sample preserved at -22°C (collected at initial evaluation or later) was available for measuring inhibin B by the same hormonal immunoassay method. Results: Among the 21 boys, 15 had normal puberty (early in two), and six had partial (n = 2) or complete (n = 4) HH. Among the 14 girls, five had normal puberty (early in one)-four with regular menses and one in the process of puberty-, four had complete HH, and five had amenorrhea (primary in three and secondary in two) after normal pubertal development, despite a normal pubertal gonadotropin response to gonadotropin-releasing hormone test. These were considered as having partial HH. Only three boys had values over the normal lower range for serum inhibin B concentrations despite partial (n = 2) or complete (n = 1) HH. Inhibin B concentrations were low in all girls with complete HH, normal in all those with partial HH except in one and in those with normal puberty except in two. Considering boys and girls together, the occurrence of under-range inhibin B was significantly higher in those with HH than in those without (47 vs. 10%, p = 0.02). All 15 patients with HH had associated thyroid-stimulating hormone and adrenocorticotropic hormone deficiency except for 3 girls with partial HH. Conclusions: Under-range inhibin B concentrations in patients with PSIS might be suggestive of HH. These concentrations provide a simple first-line predictive test, especially in boys.

Reactive oxygen species and male reproductive hormones

Reports of the increasing incidence of male infertility paired with decreasing semen quality have triggered studies on the effects of lifestyle and environmental factors on the male reproductive potential. There are numerous exogenous and endogenous factors that are able to induce excessive production of reactive oxygen species (ROS) beyond that of cellular antioxidant capacity, thus causing oxidative stress. In turn, oxidative stress negatively affects male reproductive functions and may induce infertility either directly or indirectly by affecting the hypothalamus-pituitary-gonadal (HPG) axis and/or disrupting its crosstalk with other hormonal axes. This review discusses the important exogenous and endogenous factors leading to the generation of ROS in different parts of the male reproductive tract. It also highlights the negative impact of oxidative stress on the regulation and cross-talk between the reproductive hormones. It further describes the mechanism of ROS-induced derangement of male reproductive hormonal profiles that could ultimately lead to male infertility. An understanding of the disruptive effects of ROS on male reproductive hormones would encourage further investigations directed towards the prevention of ROS-mediated hormonal imbalances, which in turn could help in the management of male infertility.

Anthropometric Measurements, Serum Reproductive Hormonal Levels and Sexual Development among Boys in the Rural Western Cape, South Africa

Data on growth and sexual maturation among boys from the rural Western Cape in South Africa is limited. A cross-sectional study of 269 school boys was conducted testing for serum luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone, sex hormone binding globulin (SHBG) and estradiol (E2); height, weight and body mass index (BMI); sexual maturity (using Tanner Stages) and a questionnaire (demographic and medical history). The median age at pubertal onset (Tanner Stage 2) and Tanner Stage 5 was 11.6 and 14.7 years, respectively. The median testicular volume was 5.5 mL at Tanner Stage 2 increasing from 2.5 mL at Tanner Stage 1 to 14.7 mL at Tanner Stage 5. Height and weight measurements were <25th & 50th percentile references at Tanner Stages 1–3. Controlling for confounders, serum FSH and LH increased (p < 0.05) from Tanner Stage 1 to 4 (by 4.1 and 3 mL respectively), and serum testosterone and estradiol increased after Tanner Stage 2 (by 12.7 nmol/L and 59.5 pmol/L respectively). These results indicate some delays in pubertal development of boys in the rural Western Cape when compared to boys from other settings possibly due to nutritional, socio-economic and environmental exposures. Changes in serum hormone levels were consistent with other populations. Initiatives to improve nutrition amongst Western Cape rural communities are recommended.

Gonadotropin-dependent precocious puberty in an 8-year-old boy with leydig cell testicular tumor

Leydig cell testicular tumors are very rare in children. They can present as gonadotropin-independent precocious puberty due to excess androgen secretion. We report the case of an 8-year-old boy with isosexual precocity whose hormonal investigation showed luteinizing hormone-independent testosterone hypersecretion. Although no palpable mass was present, scrotal ultrasound revealed a testicular tumor. Testis-sparing tumor resection was performed and the histopathology analysis showed a Leydig cell tumor. After surgery the testosterone levels remained high and further examination showed gonadotropin-dependent precocious puberty, which is believed to be likely caused by the activation of the hypothalamic-pituitary axis due to a long-term exposition to sex steroids. He is currently being treated with a long-acting gonadotropin-releasing hormone analog and the process of sexual precocity has until now been suppressed.

Spreading the clinical window for diagnosing fetal-onset hypogonadism in boys

In early fetal development, the testis secretes - independent of pituitary gonadotropins - androgens and anti-Müllerian hormone (AMH) that are essential for male sex differentiation. In the second half of fetal life, the hypothalamic-pituitary axis gains control of testicular hormone secretion. Follicle-stimulating hormone (FSH) controls Sertoli cell proliferation, responsible for testis volume increase and AMH and inhibin B secretion, whereas luteinizing hormone (LH) regulates Leydig cell androgen and INSL3 secretion, involved in the growth and trophism of male external genitalia and in testis descent. This differential regulation of testicular function between early and late fetal periods underlies the distinct clinical presentations of fetal-onset hypogonadism in the newborn male: primary hypogonadism results in ambiguous or female genitalia when early fetal-onset, whereas it becomes clinically undistinguishable from central hypogonadism when established later in fetal life. The assessment of the hypothalamic-pituitary-gonadal axis in male has classically relied on the measurement of gonadotropin and testosterone levels in serum. These hormone levels normally decline 3-6 months after birth, thus constraining the clinical evaluation window for diagnosing male hypogonadism. The advent of new markers of gonadal function has spread this clinical window beyond the first 6 months of life. In this review, we discuss the advantages and limitations of old and new markers used for the functional assessment of the hypothalamic-pituitary-testicular axis in boys suspected of fetal-onset hypogonadism.

Serum insulin-like factor 3 levels during puberty in healthy boys and boys with Klinefelter syndrome

CONTEXT

Levels of the Leydig cell-specific hormone insulin-like factor 3 (INSL3) are incompletely characterized in boys during pubertal development.

OBJECTIVE

The objective of the study was to characterize changes in INSL3 levels during spontaneous puberty in healthy boys, boys with aromatase inhibitor-induced hypergonadotropic hyperandrogenism, and boys with Leydig cell dysfunction.

DESIGN

This was a prospective clinical study.

SETTING

The study was conducted at a university hospital pediatric endocrinology outpatient clinic.

PATIENTS

Patients included 30 healthy boys with idiopathic short stature (ISS) aged 9.0-14.5 yr and 14 boys with Klinefelter syndrome (KS) aged 10-13.9 yr.

INTERVENTION

In ISS boys, intervention included aromatase inhibitor letrozole or placebo for 24 months.

MAIN OUTCOME MEASURES

Serum INSL3 levels in relation to bone age, Tanner pubertal stages, and LH and testosterone levels were measured.

RESULTS

Onset of puberty was associated with a significant increase in INSL3 levels from 0.06 +/- 0.01 ng/ml at Tanner G1 to 0.32 +/- 0.16 ng/ml at G2 (P < 0.0001). Adult INSL3 levels (> or = 0.55 ng/ml) were attained at bone age 13-14 yr. ISS boys with letrozole-induced hypergonadotropic hyperandrogenism had, after 12 months of therapy, higher INSL3 levels than did placebo treated (0.85 +/- 0.54 vs. 0.26 +/- 0.17 ng/ml, P < 0.01). In KS boys during spontaneous puberty, after an initial increase similar to that in healthy boys, INSL3 concentrations leveled off despite hyperstimulation by LH. Positive correlations occurred between serum INSL3 and LH and between INSL3 and testosterone levels in all three groups (P < 0.0001).

CONCLUSIONS

In boys, the Leydig cell-specific hormone INSL3 may serve as a new marker for onset and progression of puberty. Pubertal increase in INSL3 levels seems to depend on LH. In KS subjects, INSL3 concentrations indicate Leydig cell dysfunction from midpuberty onward.

Inhibin B is a better marker of spermatogenesis than other hormones in the evaluation of male factor infertility

OBJECTIVE

To assess the role of inhibin B in the evaluation of male factor infertility.

DESIGN

Prospective study.

SETTING

Reproductive endocrinology clinic.

PATIENT(S)

Seventy-five patients with infertility problems (mean age 31.2 +/- 7.5 years) and 12 controls (32.1 +/- 8.8 years) with proven fertility.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Semen analysis was performed according to World Health Organization guidelines. Testicular volume was assessed with the Prader's orchidometer. Serum levels of inhibin B (pg/mL), LH (mIU/mL), FSH (mIU/mL), prolactin (micro IU/mL), and testosterone (nmol/L) were assessed.

RESULT(S)

The mean +/- SEM inhibin B and testosterone levels were significantly lower in the patients than in the controls (inhibin B: 116.4 +/- 11.7 vs. 181.2 +/- 20.9, P=.008; testosterone: 13.6 +/- 0.9 vs. 25.1 +/- 2.9, P=.008). In general, sperm count and testicular volume in the patients were significantly and positively correlated with inhibin B (sperm count: r = 0.476, P<.0001; testicular volume, right: r = 0.57, P=.0001; left: r = 0.53, P=.0001); the inhibin B-FSH index was negatively correlated with FSH. Inhibin B was more strongly correlated with testicular volume and semen parameters than FSH. Inhibin B in the patients was negatively correlated with FSH (r = -0.723, P=.0001) and LH (r = -0.52, P=.0001) and was positively correlated with testosterone (r = 0.4, P=.0013).

CONCLUSION(S)

Inhibin B measurement is a better marker of fertility status than FSH and LH. Concentration of inhibin B in patients with infertility may provide useful information on spermatogenesis and possibly serve as a more direct marker of spermatogenesis than FSH.

Inhibins in female and male reproductive physiology: role in gametogenesis, conception, implantation and early pregnancy

A great deal of new information has arisen in the recent years concerning inhibin physiology and clinical relevance in reproductive medicine. It is now recognized that the two inhibin isoforms, named inhibin A and inhibin B, are produced by the gonads in the course of gamete maturation and in women have a different pattern of secretion throughout the menstrual cycle. Since inhibins are also produced by placenta and fetal membranes, it has been suggested that there is an involvement in physiological adaptation of pregnancy. Evidence from several sources has underlined the clinical usefulness of the measurement of inhibin-related proteins in the diagnosis and follow-up of different fertility disturbances and early pregnancy viability. In the male, inhibin B is produced in the testis, principally by the Sertoli cells. Inhibin B expression and secretion are positively correlated with Sertoli cell function, sperm number, and spermatogenic status and are negatively correlated with FSH. This review covers the most recent advances on the role of inhibins in human reproductive function. Considerable progress in the understanding of inhibin physiology has resulted from selective measurement of the two inhibin molecular forms, named inhibin A and B. Newly recognized alterations of inhibin levels in gynaecological diseases as well as in normal and pathological pregnancy are discussed, with particular emphasis on the potential clinical usefulness of assessing inhibin levels in serum and other biological fluids.

Altered serum profile of inhibin B, Pro-alphaC and anti-Müllerian hormone in prepubertal and pubertal boys with varicocele

OBJECTIVE

Anti-Müllerian hormone (AMH) and inhibin B are reliable markers of Sertoli cell function. The aim of the present study was to assess the functional state of Sertoli cells in order to detect early changes in the testicular function of prepubertal and pubertal patients with untreated grade II or III varicocele.

DESIGN AND PATIENTS

Seven prepubertal and 55 pubertal boys with untreated grade II or III varicocele were studied. Seven prepubertal and 43 pubertal normal boys were considered as controls.

MEASUREMENTS

Serum levels of gonadotrophins, testosterone, inhibin B and Pro-alphaC and AMH were determined by time-resolved immunofluorometric assays, radioimmunoassay (RIA) and specific enzyme-linked immunosorbent assays (ELISAs), respectively.

RESULTS

Inhibin B and Pro-alphaC serum levels were higher in prepubertal patients with varicocele than in controls (P < 0.001). No further increment in inhibin B and Pro-alphaC levels was observed in pubertal patients with varicocele. Higher levels of AMH were found in patients in Tanner stages I, III, IV and V when compared to normal boys by Tanner stage (P < 0.05, P < 0.01, P < 0.01, P < 0.001, respectively). The direct correlation found in normal boys between inhibin B levels and LH, testosterone and testicular volume was not observed in patients with varicocele.

CONCLUSIONS

The altered serum profile of gonadal hormones observed in untreated prepubertal and pubertal patients with varicocele may indicate an early abnormal regulation of the seminiferous epithelium function.

Serum levels of dimeric and monomeric inhibins and the degree of seminal alteration in infertile men with varicocele

The aim of the present study was to establish the serum levels of inhibins and their relationship with the degree of seminal alteration in infertile men. Thirty-six patients with varicocele (Va) and seven non-obstructive azoospermic men (Az) were included. The Va group was divided into two subgroups: Va I (sperm concentration: >20 x 106; n = 21) and Va II (sperm concentration: < 20 x 106; n = 15). Twelve fertile men were included as a control group (Co). Semen analysis and serum follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), inhibin B and Pro-alphaC levels were determined. Serum inhibin B and T levels were significantly lower and FSH and LH significantly higher in group Az when compared with the Co. Inhibin B was unable to differentiate Va I from Va II groups. However, in Va II an increase in FSH levels was observed. An inverse correlation between inhibin B and FSH, a direct correlation between inhibin B and testosterone, sperm concentration, motility and morphology were found. No such correlations were seen when only the Va group was analysed. The lack of correlation between serum levels of inhibin B, gonadotrophins, sperm concentration and seminal parameters observed in Va, adds other factor to the complex pathophysiology of varicocele. Finally, further studies are needed to elucidate if oligozoospermic patients with varicocele have also an impaired negative feed-back mechanism that regulates FSH synthesis and secretion.

Inhibins in childhood and puberty

Inhibin is a heterodimeric glycoprotein that consists of an alpha-subunit linked to either a betaA subunit (inhibin A) or to a betaB subunit (inhibin B) and it exists in at least six different isoforms. These isoforms can not be measured separately by immunoassays. In boys, serum inhibin B levels change in concert with the increase in gonadotrophins. Associated with the postnatal activation of gonadotrophin secretion, the early inhibin B secretion is sustained until the age of 18-24 months; thereafter serum concentrations subside. In boys, between Tanner stages G1 and G2, serum inhibin B concentration again increases, but then plateaus. Inhibin A levels in human males are below the detection limit, but in girls, during the postnatal activation of gonadotrophin secretion, both serum inhibin A and inhibin B concentrations are measurable. Serum inhibin B levels correlate positively with age several years before the clinical onset of puberty, suggesting increasing follicular activity in late prepuberty. During female puberty, the inhibin B level increases from Tanner stage B1 through stage B3, suggesting high follicular activity before the development of ovulatory menstrual cycles, but serum inhibin A levels become measurable later in puberty, in agreement with the idea that inhibin A is mainly produced by the corpus luteum.

Inhibin B in boys from birth to adulthood: relationship with age, pubertal stage, FSH and testosterone

OBJECTIVE

Inhibin B in males is produced principally by Sertoli cells under the influence of FSH and is thought to have a role in feedback regulation of FSH. The aims of our study were to investigate how inhibin B changes from birth to late adolescence in boys, to derive reference data and to explore its relation with pubertal stage, FSH and testosterone.

DESIGN AND SUBJECTS

Blood samples were collected from (i) 366 boys aged 0--18 years to obtain age-related reference data; (ii) 195 boys who had full pubertal staging; and (iii) a cohort of 15 boys studied longitudinally as they approached and entered early puberty.

MEASUREMENTS

Dimeric inhibin B was measured by double antibody enzyme-linked immunosorbent assay (ELISA), FSH by immunoradiometric assay (IRA) and testosterone by an extraction radioimmunoassay.

RESULTS

Inhibin B was high in infant boys, decreased gradually to a nadir at 6--10 years of age, then increased rapidly in early adolescence to reach a new plateau at 12--17 years. It was detectable in all samples. Age-related reference ranges and data for calculation of SD scores are presented. In prepubertal boys, inhibin B correlated positively with age (P < 0.001), but not with FSH. Inhibin B increased progressively from pubertal stages G1 to G3 but then decreased slightly at stages G4 to G5 (P less-than-or-equal 0.01). At stage G2, inhibin B correlated positively with testosterone (P < 0.01) but not with FSH. From stage G3 onwards, inhibin B correlated inversely with FSH (P < 0.01) but lost its relationship with testosterone. In the cohort of boys studied longitudinally, inhibin B increased progressively prior to pubertal onset and further on entry into early clinical puberty (P < 0.05). Testosterone also increased over this period (P < 0.05) but FSH showed no significant change.

CONCLUSIONS

The two peaks of inhibin B during infancy and early puberty appear to reflect the two periods of Sertoli cell proliferation in normal human males. During mid-childhood, a relatively constant amount of inhibin B is secreted constitutively. The early FSH-independent increase in inhibin B that precedes clinical puberty and continues to stage G2 may be stimulated by testosterone or other factors from Leydig cells. The inverse relationship between inhibin B and FSH that subsequently develops from mid-puberty onwards is consistent with the establishment of a negative feedback loop at this time.

Operation of the follicle-stimulating hormone (FSH)-inhibin B feedback loop in the control of primate spermatogenesis

This paper reviews our current understanding of the function and operation of the follicle-stimulating hormone (FSH)-inhibin feedback loop in the male rhesus monkey (Macaca mulatta). Inhibin B is the major testicular inhibin in the monkey, and the pattern of secretion of this hormone during postnatal development is temporally coupled to that of gonadotropin. Inhibin B secretion by the Sertoli cell is stimulated by FSH and inhibited by luteinizing hormone (LH), the latter presumably acting via Leydig cell production of testosterone (T). The dynamics of the FSH-inhibin B feedback loop in the adult monkey is revealed following unilateral orchidectomy (UO). Interestingly, a sustained, 50% deficit in inhibin B secretion occurs after UO and this persistent error signal, in turn, results in elevated concentrations of FSH in the circulation. The elevated secretion of FSH appears to be the principal drive for the increased sperm output by the remaining testis. Available data for the functioning of the FSH-inhibin B feedback loop in the human male are placed in perspective, and a model for the negative feedback regulation of sperm number in primates is proposed.

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).

Low serum inhibin B concentrations in male survivors of childhood malignancy

The aim of this study was to assess the value of serum inhibin B in detecting male gonadal dysfunction in childhood cancer survivors. 27 male postpubertal (Tanner's pubertal stage G5 or P6) and 12 pubertal (> or = G2) patients were drawn from the endocrine follow-up protocol of childhood cancer patients at the Paediatric Clinic of Turku University Hospital, Turku, Finland. The average time (mean +/- S.D.) between the diagnosis and this study was 11.7 +/- 4.5 years in the postpubertal and 7.0 +/- 3.9 years in the pubertal group. Serum samples for the determination of follicle-stimulating hormone (FSH), luteinising hormone (LH), oestradiol, testosterone, and inhibin A and B dimers were collected. The demographic factors, pubertal stage and testicular size of the patient were measured at the same routine outpatient visit. Serum inhibin concentrations were correlated to testicular volume and gonadotrophin concentrations. Strong correlations were observed between testicular size (r = 0.80, P < 0.001) or FSH (r = -0.58, P = 0.002) and inhibin B concentration in the postpubertal group. Inhibin A was not detectable (< 2 pg/ml). Testicular volume measurement was accurately documented in 21 postpubertal subjects. Patients with small testicles (< 10 ml) had inhibin B concentrations under 42 pg/ml and those whose testicular size was over 13 ml had inhibin B concentrations exceeding 100 pg/ml. In all 12 pubertal survivors, serum inhibin B levels were > or = 94 pg/ml, except in one case of testicular cancer where inhibin B was 8.1 pg/ml and the FSH concentration was elevated. Inhibin B seems to be an indicator of male gonadal function in postpubertal childhood cancer survivors and could be used in the estimation of gonadal function of male survivors earlier than testicular volume or semen analyses would be routinely possible. However, the correct cut-off level of serum inhibin B, as well as the details of inhibin B physiology during puberty, remain to be determined before semen analysis can be replaced by the measurement of inhibin B.