Feedback Regulation by Inhibins A and B of the Pituitary Secretion of Follicle-Stimulating Hormone

Screening and identification of nanobody against inhibin α-subunit from a Camelus bactrianus phage display library

Background

Inhibin is a member of the transforming growth factor family that influences reproduction in animals.

Objective

The purpose of this study was to obtain nanobodies from the phage antibody library constructed by us that can specifically bind to inhibin α-subunit.

Methods

In this study, camels were immunized with Kazakh sheep inhibin-α protein that expressed in BL21 E. coli, and the camel VHH nanobody phage display library was prepared using nested PCR. The nanobodies specifically binding to inhibin α-subunit in the library were screened by three rounds of immunoaffinity screening and phage enzyme-linked immunosorbent assay (phage ELISA). The functions of the selected nanobodies were identified using molecular simulation docking, ELISA affinity test, and sheep immunity test.

Results

A nanobody display library was successfully constructed with a capacity of 1.05 × 1012 CFU, and four inhibin-α-subunit-specific nanobodies with an overall similarity of 69.34 % were screened from the library, namely, Nb-4, Nb-15, Nb-26, and Nb-57. The results of molecular simulation docking revealed that four types of nanobodies were complexed with inhibin-α protein mainly through hydrophobic bonds. Immunity tests revealed that the nanobody Nb-4 could effectively inhibit sheep inhibin A/B and could significantly improve the FSH level in sheep.

Conclusion

Four inhibin α-subunit-specific nanobodies with biological functions were successfully screened. To the best of our knowledge, this is a new reproductive immunomodulatory pathway of inhibin α-subunit, which may change the secretion of FSH in the ovary, thus changing the estrous cycle of organisms.

Asprosin-induced alterations in female rat puberty and reproductive hormonal profiles

OBJECTIVE

To investigate the comprehensive effects of daily chronic asprosin administration on various pubertal and reproductive parameters in female rats. This study aims to elucidate the role of asprosin in regulating the onset of puberty and its influence on hormonal profiles and ovarian histology.

METHODS

Asprosin was administered intraperitoneally (i.p.) at a dose of 500 ng/kg daily for eight weeks. Hormonal assays and histological analyses were performed to evaluate the effects of asprosin on the onset of puberty and reproductive function.

RESULTS

Daily chronic administration of asprosin accelerated the onset of the first oestrus. Hormonal assays revealed significant elevations in serum levels of Follicle-Stimulating Hormone (FSH) and Oestradiol (E2), while Inhibin B levels decreased. Histological evaluations demonstrated an increased number of primary and secondary follicles in ovarian tissue, without affecting primordial follicle counts or reproductive organ weights.

CONCLUSIONS

Role of adipokines in regulating puberty and reproductive function has increasingly gained recognition. This study aimed to provide the first comprehensive examination of the effects of daily chronic asprosin administration on pubertal and reproductive parameters in female rats. Utilising hormonal assays and histological analyses, asprosin was administered intraperitoneally (i.p.) at a dose of 500 ng/kg, daily, for eight weeks. Our findings revealed that daily chronic administration of asprosin accelerated the onset of the first oestrus. Hormonal assays showed significant elevations in serum levels of Follicle-Stimulating Hormone (FSH) and Oestradiol (E2), while Inhibin B levels decreased. Histological evaluations demonstrated an increased number of primary and secondary follicles in ovarian tissue, without affecting primordial follicle counts or reproductive organ weights. These results provide new insights into asprosin's role in advancing the age of first oestrus and modulating hormonal profiles, thereby offering potential benefits to the female reproductive system.

Glycyrrhizae radix et Rhizoma-Derived Carbon Dots and Their Effect on Menopause Syndrome in Ovariectomized Mice

With the extension of the human life span and the increasing pressure of women's work and life, menopause syndrome (MPS) refers to a problem that puzzles almost all women worldwide. Hormone replacement treatment (HRT) can effectively mitigate the symptoms but can also exert adverse effects to a certain extent. Glycyrrhizae radix et rhizome (GRR) is commonly made into a charcoal processed product, termed GRR Carbonisatas (GRRC), for use in traditional Chinese medicine (TCM). GRRC is widely used to treat MPS and other gynecological diseases. In this study, GRRC was prepared through pyrolysis. Subsequently, GRR-derived carbon dots (GRR-CDs) were purified through dialysis and characterized using transmission electron microscopy, high-resolution transmission electron microscopy, Fourier-transform infrared, ultraviolet, fluorescence, X-ray photoelectron microscopy, and high-performance liquid chromatography. The effects of GRR-CDs on MPS were examined and confirmed using ovariectomized female mice models. The GRR-CDs ranged from 1.0 to 3.0 nm in diameter and with multiple surface chemical groups, as indicated by the results. GRR-CDs can elevate the estradiol (E2) level of healthy female mice. Moreover, GRR-CDs can alleviate MPS using the typical ovariectomized mice model, as confirmed by elevating the estradiol (E2) level and reducing the degree of follicle stimulating hormone (FSH) and luteinizing hormone (LH) and raising the degree of uterine atrophy. The results of this study suggested that GRR-CDs may be a potential clinical candidate for the treatment of MPS, which also provides a possibility for nanodrugs to treat hormonal diseases.

Influence of ethnicity on biochemical markers of health and disease in the CALIPER cohort of healthy children and adolescents

Background Accurate pediatric reference intervals (RIs) for laboratory tests determined in a healthy pediatric population are essential for correct laboratory test interpretation and clinical decision-making. In pediatrics, RIs require partitioning by age and/or sex; however, the need for partitioning based on ethnicity is unclear. Here, we assessed the influence of ethnicity on biomarker concentrations in the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) cohort of healthy children and adolescents and compared the results with the National Health and Nutrition Examination Survey (NHANES). Methods A total of 52 biomarkers were measured in a multiethnic population of 846-1179 healthy children (aged 5 to <19 years) upon informed consent. Biomarker concentrations were retrospectively compared between four major ethnic groups (i.e. Black, Caucasian, East Asian, and South Asian, determined by parental ethnicity). Retrospective results were verified prospectively using an additional 500 healthy pediatric samples with equal sample size across ethnicities. Ethnic-specific differences were assessed based on statistical significance and biological and analytical variations. Appropriate age-, sex-, and ethnic-specific RIs were calculated. Results Ethnic-specific differences were not observed for 34 biomarkers examined in the retrospective analysis, while 18 demonstrated statistically significant ethnic differences. Among these, seven analytes demonstrated ethnic-specific differences in the prospective analysis: vitamin D, amylase, ferritin, follicle-stimulating hormone (FSH), immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM). Analysis of select NHANES data confirmed CALIPER findings. Conclusions This is the first comprehensive Canadian pediatric study examining ethnic-specific differences in common biomarkers. While the majority of biomarkers did not require ethnic partitioning, ethnic-specific RIs were established for seven biomarkers showing marked differences. Further studies in other populations are needed to confirm our findings.

Dynamic Changes in Serum Inhibin B Levels in 6- to 24-Month-Old Children Receiving Cryptorchidism Surgery

Objective

Cryptorchidism is the most common congenital disability and is defined as the absence of one or both testicles in the scrotum during fetal development. In patients with cryptorchidism, lowered serum inhibin B levels suggest testicular dysfunction. The practical application of serum inhibin B levels in childhood remains controversial. The purpose of this study was to observe the post-operational changes of serum inhibin B levels in patients with cryptorchidism and provide evidence that serum inhibin B is a potential marker for the efficacy of testicular surgery.

Methods

A total of 83 male children with cryptorchidism were enrolled in this study. All the children had blood samples taken by venipuncture on the day of surgery. The serum inhibin B levels in the blood samples were measured using an ELISA kit. Paired t-tests were used to assess differences between the groups.

Results

The results show that, compared with the preoperative values, there was a statistically significant increase in serum inhibin B values one month after the operation in each group (P < 0.05). Compared with the one-month post-operation results, there were no significant changes six months after operation in each group (P>0.05). However, serum inhibin B values decreased significantly in all groups at 12 months post-operation (P < 0.05), suggesting that serum inhibin B values are significantly correlated with age. Correlation analysis showed that serum inhibin B was negatively correlated with age from 6 to 36 months, and the correlation coefficient was −0.488.

Conclusion

Serum inhibin B can be used as a short-term evaluation index of cryptorchidism surgery rather than as a long-term indicator.

Insights and clinical potential of proteomics in understanding spermatogenesis

Introduction: With the worldwide decline on male fertility potential, the importance of the insight of the spermatogenic process has been increasing. In recent years, proteomic methodologies have been applied to seminal fluid of infertile men to search for infertility potential biomarkers. However, to understand the spermatogenic event and to search for treatment to spermatogenic impairment, comparative analysis of testicular proteomics is considered a powerful methodology.Areas covered: Herein, we present a critical overview of the studies addressing proteomic alterations in the development of spermatogenesis during puberty, as well as during the different phases of the spermatogenic event. The comparative studies of the proteomic testicular profile of men with and without spermatogenic impairment are also discussed and key proteins and pathways involved highlighted.Expert opinion: The usage of whole human testicular tissue with its heterogeneous cellular composition makes proteome data interpretation particularly challenging. This may be minimized by controlled experiments involving the collection of testicular tissue and sperm from the same individuals, integrated in a clinically characterized cohort of healthy and infertile men. The analysis of specific subcellular proteomes can add more information to the proteomic puzzle, opening new treatment possibilities for infertile/subfertile men.

Molecular characterization of inhibin-A: Structure and expression analysis in Clarias batrachus

The inhibins are disulphide-linked heterodimeric glycoproteins that belong to the TGFβ superfamily. Inhibins have been well studied in mammals but the information about their structure and function is very limited in lower vertebrates. The aim of the present study was to characterize inhibin-A and to understand its receptor binding interaction, and to evaluate its biological function in Clarias batrachus. Structure prediction of inhibin-A revealed two glycosylation sites on inhibin-α (Asp262 and Asn334). Docking of inhibin-A with its receptor; betaglycan and Act RIIA showed that residues Ser321, Gly324 and Leu325 of inhibin-α are involved in high affinity binding with betaglycan while inhibin-βA bound to Act RIIA by forming hydrogen bonds. The mRNA transcript analysis of various tissues indicated the presence of higher to moderate expression of inhibin-α and inhibin-βA in the gonads and the extra-gonadal tissues. Further, stage specific expression showed decreased levels of inhibin-α in the gonads during the annual reproductive cycles. Inhibin-βA, activin-βB and Act RIIA increased in the brain during spawning while FSHr increased in the gonads during the preparatory phase. Our study provides molecular, structural and functional insights of inhibin-A for the first time in C. batrachus.

Hypogonadism in male thalassemia major patients: pathophysiology, diagnosis and treatment

Failure of pubertal growth, delay or absence of sexual development, infertility and sexual dysfunction due to hypogonadism and defective spermatogenesis are frequent and well recognized disturbances among male patients with transfusion dependent (TD) thalassaemia major (β-thal). These problems are attributed mainly to the damage caused by chronic anaemia and the deposition of excess iron in the pituitary gland and testicles. This is a short review of male pubertal disorders in patients with β-thal written by pediatric endocrinologists and haematologists with an interest and active involvement, in the diagnosis and management of these complications in this group of patients. A vigilant clinical evaluation of growth and puberty, as well as an appropriate hormonal evaluation in poly-transfused (TD β-thal) patients is strongly recommended for early detection and treatment of endocrine dysfunction. Of crucial importance also, is the implementation of an efficient chelation regime from early life, to prevent severe iron load and permanent damage to the endocrine glands, particularly those responsible for gonadal function.

Toxic metabolites, Sertoli cells and Y chromosome related genes are potentially linked to the reproductive toxicity induced by mequindox

Mequindox (MEQ) is a relatively new synthetic antibacterial agent widely applied in China since the 1980s. However, its reproductive toxicity has not been adequately performed. In the present study, four groups of male Kunming mice (10 mice/group) were fed diets containing MEQ (0, 25, 55 and 110 mg/kg in the diet) for up to 18 months. The results show that M4 could pass through the blood-testis barrier (BTB), and demonstrate that Sertoli cells (SCs) are the main toxic target for MEQ to induce spermatogenesis deficiency. Furthermore, adrenal toxicity, adverse effects on the hypothalamic-pituitary-testicular axis (HPTA) and Leydig cells, as well as the expression of genes related to steroid biosynthesis and cholesterol transport, were responsible for the alterations in sex hormones in the serum of male mice after exposure to MEQ. Additionally, the changed levels of Y chromosome microdeletion related genes, such as DDX3Y, HSF2, Sly and Ssty2 in the testis might be a mechanism for the inhibition of spermatogenesis induced by MEQ. The present study illustrates for the first time the toxic metabolites of MEQ in testis of mice, and suggests that SCs, sex hormones and Y chromosome microdeletion genes are involved in reproductive toxicity mediated by MEQ in vivo.

Activin/follistatin system in grass carp pituitary cells: - Regulation by local release of growth hormone and luteinizing hormone and its functional role in growth hormone synthesis and secretion

Gonadotrophin regulation by activin/follistatin system is well-documented, but the corresponding effect on growth hormone (GH) has not been fully characterized and with little information available in lower vertebrates, especially in fish models. In grass carp, local interactions of GH and luteinizing hormone (LH) can induce GH release and gene expression at pituitary level via autocrine/paracrine mechanisms. To shed light on the role of activin/follistatin system in GH regulation by local actions of GH and LH, grass carp activin βA and βB were cloned, shown to be single-copy genes expressed in the pituitary, and confirmed to encode activin proteins capable of transactivating promoter with activin-responsive elements. In grass carp pituitary cells, activin A and B were effective in reducing GH secretion and GH cell content with concurrent drop in GH mRNA level whereas the opposite was true for follistatin, the activin-binding protein known to neutralize the effects of endogenous activin. Treatment with activin A and B not only could suppress basal but also inhibit GH mRNA expression induced by GH and human chorionic gonadotropin (hCG), a functional analogue of LH in fish model. Apparently, down-regulation of GH mRNA by activin was mediated by reducing GH transcript stability with concurrent inhibition on GH promoter activity via the SMAD pathway. In reciprocal experiments, GH treatment was found to up-regulate activin βA, activin βB and follistatin mRNA levels in carp pituitary cells but the opposite was noted by removing endogenous GH with GH antiserum. Interestingly, parallel treatment with hCG could also inhibit basal as well as GH-induced activin βA, activin βB and follistatin gene expression. These results, as a whole, indicate that the pituitary activin/follistatin system can serve as a regulatory target for local interactions of GH and LH and contribute to GH regulation by autocrine/paracrine mechanisms in the carp pituitary.

Inhibin-B secretion and FSH isoform distribution may play an integral part of follicular selection in the natural menstrual cycle

The aim of the present paper is to expand the concept on how follicular selection takes place in the follicular phase of the natural menstrual cycle. It is suggested that inhibin-B exerts a more intimate role in this process than previously understood. Inhibin-B shows a peak in the circulation around cycle day 7, simultaneous with selection of the dominant follicle, whereas levels of estradiol and inhibin-A only start to increase a few days later suggesting that inhibin-B is mainly responsible for downregulating pituitary FSH release. New data now demonstrate that the circulatory peak of inhibin-B is reflected by peak production of inhibin-B, in contrast to inhibin-A, in the selected follicle with a diameter of 10-12 mm, where concentrations are one thousand times higher than in the circulation. This high inhibin-B concentration also exerts paracrine effects, stimulating theca cell androgen production in concert with LH. New data now suggest that in the corresponding granulosa cells androgens upregulate FSH receptor (FSHR) and LH receptor (LHR) mRNA expression, which in turn stimulate CYP19a mRNA expression providing the follicles which most effectively undertake these processes with the best chance of becoming selected. Inhibin-B production is stimulated by FSH and it appears that the acidic isoforms of FSH induce inhibin-B secretion most efficiently thereby, for the first time, placing the changing FSH isoform profile during the follicular phase in a physiological context. Collectively, it appears that inhibin-B is an integral part of follicular selection in the normal menstrual cycle, exerting both endocrine and paracrine effects and facilitating continued growth of the selected follicle.

Fluoride exposure changed the structure and the expressions of reproductive related genes in the hypothalamus-pituitary-testicular axis of male mice

Numerous studies have shown that fluoride exposure adversely affected the male reproductive function, while the molecular mechanism is not clear. The present study was to investigate the effects of fluoride exposure (60 days) on the expressions of reproductive related genes, serum sex hormone levels and structures of the hypothalamus-pituitary-testicular axis (HPTA), which plays a vital role in regulating the spermatogenesis in male mice. In this study, 48 male mice were administrated with 0, 25, 50, and 100 mg/L NaF through drinking water. Results showed that the malformation ratio of sperm was significantly increased (P<0.05). At transcriptional level, the expression levels of follicle-stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR), inhibin alpha (INHα), inhibin beta-B (INHβB), and sex hormone binding globulin (SHBG) mRNA in testis were significantly decreased (P<0.05). Moreover, histological lesions in testis and ultrastructural alterations in hypothalamus, pituitary and testis were obvious. However, the same fluoride exposure did not lead to significant changes of related mRNA expressions in hypothalamus and pituitary (P>0.05). Also, there were no marked changes in serum hormones. Taken together, we conclude that the mechanism of HPTA dysfunction is mainly elucidated through affecting testes, and its effect on hypothalamus and pituitary was secondary at exposure for 60 days.

Dynamics of the ovarian reserve and impact of genetic and epidemiological factors on age of menopause

The narrow standard age range of menopause, ∼50 yr, belies the complex balance of forces that govern the underlying formation and progressive loss of ovarian follicles (the "ovarian reserve" whose size determines the age of menopause). We show here the first quantitative graph of follicle numbers, distinguished from oocyte counts, across the reproductive lifespan, and review the current state of information about genetic and epidemiological risk factors in relation to possible preservation of reproductive capacity. In addition to structural X-chromosome changes, several genes involved in the process of follicle formation and/or maintenance are implicated in Mendelian inherited primary ovarian insufficiency (POI), with menopause before age 40. Furthermore, variants in a largely distinct cohort of reported genes-notably involved in pathways relevant to atresia, including DNA repair and cell death-have shown smaller but additive effects on the variation in timing of menopause in the normal range, early menopause (age <45), and POI. Epidemiological factors show effect sizes comparable to those of genetic factors, with smoking accounting for about 5% of the risk of early menopause, equivalent to the summed effect of the top 17 genetic variants. The identified genetic and epidemiological factors underline the importance of early detection of reproductive problems to enhance possible interventions.

Expression profiles of Fsh-regulated ovarian genes during oogenesis in coho salmon

The function of follicle-stimulating hormone (Fsh) during oogenesis in fishes is poorly understood. Using coho salmon as a fish model, we recently identified a suite of genes regulated by Fsh in vitro and involved in ovarian processes mostly unexplored in fishes, like cell proliferation, differentiation, survival or extracellular matrix (ECM) remodeling. To better understand the role of these Fsh-regulated genes during oocyte growth in fishes, we characterized their mRNA levels at discrete stages of the ovarian development in coho salmon. While most of the transcripts were expressed at low levels during primary growth (perinucleolus stage), high expression of genes associated with cell proliferation (pim1, pcna, and mcm4) and survival (ddit4l) was found in follicles at this stage. The transition to secondary oocyte growth (cortical alveolus and lipid droplet stage ovarian follicles) was characterized by a marked increase in the expression of genes related to cell survival (clu1, clu2 and ivns1abpa). Expression of genes associated with cell differentiation and growth (wt2l and adh8l), growth factor signaling (inha), steroidogenesis (cyp19a1a) and the ECM (col1a1, col1a2 and dcn) peaked in vitellogenic follicles, showing a strong and positive correlation with transcripts for fshr. Other genes regulated by Fsh and associated with ECM function (ctgf, wapl and fn1) and growth factor signaling (bmp16 and smad5l) peaked in maturing follicles, along with increases in steroidogenesis-related gene transcripts. In conclusion, ovarian genes regulated by Fsh showed marked differences in their expression patterns during oogenesis in coho salmon. Our results suggest that Fsh regulates different ovarian processes at specific stages of development, likely through interaction with other intra- or extra-ovarian factors.

Inhibin at 90: from discovery to clinical application, a historical review

When it was initially discovered in 1923, inhibin was characterized as a hypophysiotropic hormone that acts on pituitary cells to regulate pituitary hormone secretion. Ninety years later, what we know about inhibin stretches far beyond its well-established capacity to inhibit activin signaling and suppress pituitary FSH production. Inhibin is one of the major reproductive hormones involved in the regulation of folliculogenesis and steroidogenesis. Although the physiological role of inhibin as an activin antagonist in other organ systems is not as well defined as it is in the pituitary-gonadal axis, inhibin also modulates biological processes in other organs through paracrine, autocrine, and/or endocrine mechanisms. Inhibin and components of its signaling pathway are expressed in many organs. Diagnostically, inhibin is used for prenatal screening of Down syndrome as part of the quadruple test and as a biochemical marker in the assessment of ovarian reserve. In this review, we provide a comprehensive summary of our current understanding of the biological role of inhibin, its relationship with activin, its signaling mechanisms, and its potential value as a diagnostic marker for reproductive function and pregnancy-associated conditions.

Initiation of active immunization against testosterone during early puberty alters negative feedback regulation of the hypothalamic-pituitary-testicular axis in rabbits

To investigate the effects of antitestosterone immunization, initiated during early puberty, on hypothalamic-pituitary-testicular feedback in rabbits, 16 early pubertal male rabbits were randomly allocated into 2 groups (n = 8), control or immunized against testosterone-3(O-carboxymethyl)oxime-BSA in Freund adjuvant at 4 mo of age (with a booster immunization 4 wk later). Blood samples (for antibody titers and hormone concentrations) were collected at 2- or 4-wk intervals after immunization. Compared with controls, antitestosterone immunization triggered: a substantial and sustained antibody response (P < 0.01); increases in serum concentrations of luteinizing hormone (LH) and testosterone and testis weight and volume (P < 0.05); hyperplasia of testicular interstitial tissue with clustered and hypertrophic Leydig cells; and greater (P < 0.05) enzyme protein and messenger RNA (mRNA) expression levels for testicular cholesterol side-chain cleavage cytochrome P-450, 17α-hydroxylase cytochrome P-450, and 3β-dydroxysteroid dehydrogenase. Furthermore, immunoneutralization of testosterone upregulated mRNA expressions for genes in sex steroid negative feedback loops, including androgen receptor (AR), estrogen receptor alpha (ER-α), kisspeptin encoded gene (kiss-1) and kisspeptin receptor (G-coupled receptor 54) and gonadotropin-releasing hormone (GnRH) in the hypothalamic arcuate nucleus, GnRH receptor and LH-β in pituitary, and AR, inhibin-α and βA subunits in testes (P < 0.05). However, immunization did not affect mRNA expressions for follicle-stimulating hormone β, AR, and ER-α in pituitary, or ER-α in testes. We concluded that antitestosterone immunization in male rabbits, initiated during early puberty, increased GnRH mRNA expression, and in turn LH synthesis by reducing testicular feedback signaling. Reduction of direct steroidal effects on the testis may also have increased testosterone secretion. Consequently, there was an accelerated testicular development during puberty and enhanced testicular function after puberty, which likely conferred prolonged reproductive advantages.

Serum inhibin A and inhibin B levels in epithelial ovarian cancer patients

The aim

of our study was to examine serum inhibin A and inhibin B concentrations in ovarian cancer patients in relation to clinicopathological features and 5-year survival.

Material and Methods

We enrolled 90 epithelial ovarian cancer patients in our study, aged 45–81 years, who underwent optimal cytoreductive surgery. In all patients, serum inhibin A and inhibin B concentrations were measured using a two-step sandwich type enzyme immunoassay before surgery.

Results

In the group of patients with ovarian cancer median serum concentration of inhibin A was 3.87 pg/mL (0.96–10.09) and inhibin B was 13.9 pg/mL (5.1–45.0). Median concentrations of inhibin A and B in relation to FIGO stage and histological subtype did not differ significantly. Inhibin A levels were significantly higher in patients with lower grading (G1 and G2) in comparison to those with higher grade G3 (p = 0.001). There were no differences in inhibin B concentrations in relation to grading. The Kaplan-Meier analyses demonstrated no differences in survival rate in relation to inhibin A levels, while there was a stepwise impairment of 5-years survival with increased inhibin B level. In the group of patients with inhibin B levels higher than 20 pg/ml the survival rate was lower (p = 0,00625, log-rank test).

Conclusion

1. Higher inhibin A serum levels were found in patients with highly differentiated ovarian carcinoma compared to the group of patients with a poorly differentiated cancer, which may confirm the influence of inhibin A on cell proliferation processes. 2. A significant importance of inhibin B was demonstrated in the prediction of death within less than a five year period. The probability of survival in patients featuring high inhibin B levels was lower with statistical significance. This may indicate the need for further studies on how to block the inhibin B activation pathway in the ovarian carcinoma therapy.

Novel aspects of the endocrinology of the menstrual cycle

Ovarian control of gonadotrophin secretion is normally achieved via the feedback mechanisms mediated by oestradiol and progesterone. Evidence has been provided that nonsteroidal substances, such as inhibin A and B, participate in the negative feedback control of FSH secretion. Another nonsteroidal ovarian substance is gonadotrophin surge-attenuating factor (GnSAF), the activity of which is particularly evident in women undergoing ovulation induction. Accumulating evidence has suggested that GnSAF plays a physiological role during the menstrual cycle. In particular, this factor antagonizes the sensitizing effect of oestradiol on the pituitary response to gonadotrophin-releasing hormone during the follicular phase of the cycle. A hypothesis has been developed that, in the late follicular phase, the activity of GnSAF is reduced and this facilitates the sensitizing effect of oestradiol on the pituitary, thus enforcing the massive discharge of gonadotrophins at the midcycle LH surge. The interaction of oestradiol, progesterone and GnSAF on the hypothalamic-pituitary system provides a novel approach to explain the mechanisms which control LH secretion during the normal menstrual cycle. The ovarian control of gonadotrophin secretion during the normal menstrual cycle is achieved via negative and positive feedback mechanisms. The steroids oestradiol and progesterone are the main regulators; however, nonsteroidal substances, such as inhibin A and inhibn B, also participate. Accumulating evidence has demonstrated that another nonsteroidal ovarian substance, gonadotrophin surge-attenuating factor (GnSAF), plays a key role in the control of LH secretion during the follicular phase and at midcycle, providing thus a novel aspect in the ovarian control of gonadotrophin secretion during the human menstrual cycle. The ovarian control of gonadotrophin secretion during the normal menstrual cycle is achieved via negative and positive feedback mechanisms. The steroids oestradiol and progesterone are the main regulators; however, nonsteroidal substances, such as inhibin A and inhibn B, also participate. Accumulating evidence has demonstrated that another nonsteroidal ovarian substance, gonadotrophin surge-attenuating factor (GnSAF), plays a key role in the control of LH secretion during the follicular phase and at midcycle, providing thus a novel aspect in the ovarian control of gonadotrophin secretion during the human menstrual cycle.

Summary of the HESI consortium studies exploring circulating inhibin B as a potential biomarker of testis damage in the rat

The Developmental and Reproductive Toxicity Technical Committee of the Health and Environmental Sciences Institute hosted a working consortium of companies to evaluate a new commercially available analytic assay for Inhibin B in rat serum or plasma. After demonstrating that the kit was stable and robust, the group performed a series of independent pathogenesis studies (23 different compound/investigator combinations) designed to examine the correlation between the appearance of lesions in the testis and changes in circulating levels of Inhibin B. These studies were reported individually in the previous articles in this series (this issue), and are discussed in this paper. For roughly half of these exposures, lesions appeared well before Inhibin B changed. A few of the studies showed a good correlation between seminiferous tubule damage and reduced circulating Inhibin B levels, while for seven exposures, circulating Inhibin B was reduced with no detectable alteration in testis histology. Whether this indicates a prodromal response or a false-positive signal will require further investigation. These exceptions could plausibly suggest some value of circulating Inhibin B as a useful biomarker in some circumstances. However, for roughly half of these exposures, Inhibin B appeared to be a lagging biomarker, requiring significant damage to the seminiferous tubules before a consistent and credible reduction in circulating levels of Inhibin B was observed.

The inhibin B response to the testicular toxicant 1, 3 dinitrobenzene in male rats

BACKGROUND

This study was conducted as part of an ILSI-HESI International Life Sciences Institute-Health & Environmental Sciences Institute consortium effort to assess the utility of circulating Inhibin B as an early biomarker of Sertoli cell-specific testicular toxicity in rats. 1, 3-Dinitrobenzene (1,3-DNB) was selected as a testicular toxicant in this study as it is known to target Sertoli cells.

METHODS

1,3-DNB (2 and 6 mg/kg/day) or control (corn oil) was administered orally to male rats for two or five consecutive days. Blood was collected from rats treated for 2 days on days 1 and 2 and from rats treated for 5 days on days 1, 3, and 5. The resulting serum was evaluated for Inhibin B and follicle stimulating hormone. At the end of the treatment periods, the testes were removed, weighed, and examined histopathologically.

RESULTS

Daily administration of 1,3-DNB resulted in decreased testis weight only on day 5 and only at the high dose (6 mg/kg/day). There was a time-dependent increase in incidence and severity of testicular findings characterized by degeneration of the germinal epithelium with loss of pachytene spermatocytes and vacuolization of the Sertoli cells in the seminiferous tubules at the high dose. Inhibin B levels in 1,3-DNB-treated animals were decreased with treatment only on day 5 at the high dose; there were no associated changes in follicle stimulating hormone.

CONCLUSIONS

Changes in serum Inhibin B levels were detected only in association with moderate or severe testicular toxicity as evidenced by histopathology and is therefore considered to be of limited value as a biomarker for Sertoli cell toxicity.

Inhibin B in plasma samples from male volunteer panel selected for health but not fertility: sources of variability

BACKGROUND

Inhibin B was measured in plasma samples obtained from 34 healthy male subjects selected on criteria typical for a phase I clinical trial across a wide age range (19-70 years).

METHODS

Mutiple samples (up to seven per subject) were obtained as a set consisting of one baseline sample then three pairs of morning and evening samples. This allowed assessment of the fed/fasted state and diurnal effects. Samples were analyzed using a commercially available inhibin B ELISA assay. Across all time points, the mean plasma inhibin B was 197 pg/ml ± 67pg/ml.

RESULTS

The results confirmed a diurnal effect where inhibin B concentration is on average about 40 pg/ml greater in the morning and showed a negative influence of age on inhibin B concentrations. There was no overt influence of body mass index on inhibin B. A variance components analysis revealed that more than 80% of the total variability was due to the variability observed between individuals. Within the fed-fasted sampling schedule of this study, inhibin B levels were slightly lower when volunteers had eaten but the magnitude of this effect was within the variance encountered between occasions.

CONCLUSION

These results illustrate that when undertaking longitudinal monitoring of inhibin B in clinical trials as means of monitoring testicular function, it is important to obtain samples from an individual at the same time of day and to use statistical methods which analyze the magnitude of deviation of an individual from their personal baseline as well as looking at group means and influence of study duration.

Cell-type specific modulation of pituitary cells by activin, inhibin and follistatin

Activins are multifunctional proteins and members of the TGF-β superfamily. Activins are expressed locally in most tissues and, analogous to the actions of other members of this large family of pleiotropic factors, play prominent roles in the regulation of diverse biological processes in both differentiated and embryonic stem cells. They have an essential role in maintaining tissue homeostasis in the adult and are known to contribute to the developmental programs in the embryo. Activins are further implicated in the growth and metastasis of tumor cells. Through distinct modes of action, inhibins and follistatins function as antagonists of activin and several other TGF-β family members, including a subset of BMPs/GDFs, and modulate cellular responses and the signaling cascades downstream of these ligands. In the pituitary, the activin pathway is known to regulate key aspects of gonadotrope functions and also exert effects on other pituitary cell types. As in other tissues, activin is produced locally by pituitary cells and acts locally by exerting cell-type specific actions on gonadotropes. These local actions of activin on gonadotropes are modulated by the autocrine/paracrine actions of locally secreted follistatin and by the feedback actions of gonadal inhibin. Knowledge about the mechanism of activin, inhibin and follistatin actions is providing information about their importance for pituitary function as well as their contribution to the pathophysiology of pituitary adenomas. The aim of this review is to highlight recent findings and summarize the evidence that supports the important functions of activin, inhibin and follistatin in the pituitary.

Expression of inhibin/activin proteins and receptors in the human hypothalamus and basal forebrain

The inhibin/activin family of proteins is known to have a broad distribution of synthesis and expression in many species, as well as a variety of functions in reproductive and other physiological systems. Yet, our knowledge regarding the production and function of inhibin and activin in the central nervous system is relatively limited, especially in humans. The present study aimed to explore the distribution of inhibin/activin protein subunits and receptors in the adult human brain. The human hypothalamus and surrounding basal forebrain was examined using post-mortem tissues from 29 adults. Immunocytochemical studies were conducted with antibodies directed against the inhibin/activin α, βA, and βB subunits, betaglycan and the activin type IIA and IIB receptors. An immunoassay was also utilised to measure dimeric inhibin A and B levels in tissue homogenates of the infundibulum of the hypothalamus. Robust βA subunit immunoreactivity was present in the paraventricular, supraoptic, lateral hypothalamic, infundibular, dorsomedial and suprachiasmatic nuclei of the hypothalamus, in the basal ganglia, and in the nucleus basalis of Meynert. A similar staining distribution was noted for the βB subunit, betaglycan and the type II receptor antibodies, whereas α subunit staining was not detected in any of the major anatomical regions of the human brain. Inhibin B immunoreactivity was present in all tissues, whereas inhibin A levels were below detectable limits. These studies show for the first time that the inhibin/activin protein subunits and receptors can be co-localised in the human brain, implicating potential, diverse neural functions.