Localization of alpha-inhibin-31 in rodent testis and brain by immunocytochemical procedure and Western blot analysis

Molecular characterization and expression pattern of inhibin α and βb in Chinese tongue sole (Cynoglossus semilaevis)

Inhibin plays important roles in vertebrate reproduction and development. In this study, we have cloned two genes encoding inhibin subunits, inhα and ihnβb, in Chinese tongue sole. inhα consists of 1032 bp, encoding a 343 amino-acid protein. inhβb is composed of 1275 bp, encoding a 424 amino-acid protein. Phylogenetic tree analysis indicated that INHα and INHβB were independently evolved. qPCR showed that inhα expression of in male testis was higher than that in ovary and pseudomale testis, while the expression of inhβb in ovary was higher than that in male and pseudomale testis. During gonadal developmental stages, inhα expression reached highest at 120 days post hatching (dph) both in ovary and testis, then showed decline in ovary but it was first decreased and then increased in the testis. Similarly, inhβb expression in ovary was low at 50-80 dph. At 120 dph, its expression was significantly increased to the peak level, and then gradually decreased. inhβb expression in testis maintained at a low level. During the embryonic developmental stages, inhα displayed the highest expression at 32-cell stage, whereas inhβb reached the highest expression at blastula stages. In situ hybridization data showed that both of inhα and inhβb were detected in oocytes of all stages. In male testis, inhα and inhβb was localized in spermatogonia, spermatocytes, spermatozoa, sertoli and leydig cells. In pseudomale testis, inhα showed the similar pattern in male testis, while the inhβb was detected in spermatocytes and spermatozoa. These data suggested that inhα may participate the spermatogenesis and oogenesis of Chinese tongue sole, while inhβb might predominantly function in oogenesis.

Evidence for the presence of immunoreactive inhibin in extragonadal tissues of ovariectomized ewes

Six ewes were ovariectomized to determine the immediate and long-term effects of removal of ovaries on the immunoreactive concentrations of FSH, LH and inhibin. Three months after ovariectomy, ewes were slaughtered and tissue samples of brain, pituitary, spleen, liver, perirenal fat, lung, kidney, adrenals and uterus were collected to determine the immunoreactive inhibin content. Both gonadotrophins, FSH and LH, increased significantly after ovariectomy. The increase of FSH, however, was more pronounced and remarkably faster than the changes of LH after ovariectomy. Immunoreactive concentrations of inhibin decreased sharply as early as 15 min after ovariectomy and subsequently decreased more gradually until 2 weeks after surgery. From this moment on, the level stabilized at 56% of the initial value. In control ewes, a considerable amount of immunoreactive inhibin is found in tissue samples of ovary, lung, kidney, pituitary and spleen. After ovariectomy, the level of immunoreactive inhibin decreased in spleen and lung samples while an important increase of immunoreactive inhibin is found in adrenals and pituitary. These results demonstrate a differential regulation of LH and FSH after ovariectomy and support an involvement of inhibin only in the immediate changes of FSH after ovariectomy in sheep. They further suggest that the adrenals and the pituitary may be extragonadal sources of inhibin. To explore the eventual contribution of the adrenals to circulating inhibin, dexamethasone (1.4 mg/ewe) and ACTH (200 IU/ewe) were in a following experiment injected intravenously in control and ovariectomized ewes. The lack of any effect of dexamethasone or ACTH on the plasma concentration of immunoreactive inhibin indicate that adrenal inhibin probably does not contribute to circulating inhibin.

Effects of alpha-inhibin-92 fragments and alpha-inhibin-92 antiserum on the control of follicle-stimulating hormone release in male rats

Alpha-inhibin-92 (alpha-IB-92) has been characterized from human seminal plasma and found to be active in suppressing FSH release in vitro and in vivo. In order to determine if smaller fragments of this 92 amino acid peptide would still be active to suppress FSH release, we have evaluated 5 of these fragments for their effects on FSH and LH release in the present study. Five alpha-IB-92 fragments (1-34, 1-46, 35-65, 35-92 and 66-92) were synthesized and injected intravenously (iv) into castrated adult rats (2 days post operation). Only fragments alpha-IB-92-(35-65) and alpha-IB-92-(66-92) significantly lowered plasma FSH, but not LH, at doses of 10 micrograms. These fragments exerted a preferential FSH-suppressing effect, but their activities were less than that of alpha-IB-92. In view of the rapid action of these peptides and the preferential FSH suppressing effect, they could be useful clinically to suppress FSH release. To determine the possible physiologic significance of alpha-IB-92, we injected antiserum raised against alpha-IB-92 into immature male rats and evaluated its effects on FSH and LH release. Normal rabbit serum (NRS) or anti-alpha-IB-92 serum was injected iv through indwelling jugular catheters into conscious, unrestrained 18 day-old male rats. Blood samples (0.2 ml) were collected at various intervals. Intravenous injection of alpha-IB-92 antiserum (0.1 ml/rat) selectively elevated plasma levels of FSH but not LH from 2-8 h post-injection in 18 day-old male rats (P < 0.01). Since immunoneutralization of alpha-IB-92 significantly elevated FSH release in immature rats, alpha-IB-92 has a physiological inhibiting role in control of FSH but not LH release at this stage of development.

Inhibin: unity in diversity

Historically, inhibin was thought to be a testicular hormone involved in the regulation of pituitary FSH by a negative feedback control. The ability of inhibin to preferentially suppress FSH without affecting LH triggered extensive research for its possible use as a male contraceptive, suggesting a plurality of molecular forms and a multiplicity of biological actions of this putative hormone. It also became evident that inhibin is not unique to the testis, as presumed earlier, and can even be obtained from the ovary. This has necessitated a fundamental revision of the original concept of inhibin. Unfortunately, not many perceive inhibin as a loose conglomerate of structurally dissimilar, FSH-suppressing proteins and insist on singling out a 32-kDa protein derived from ovarian follicular fluid to be designated as inhibin. This article highlights features common to two distinctly different types of inhibin: seminal inhibin and ovarian inhibin. Evidence is also provided to indicate that the term inhibin need not be specific to the ovarian protein, but encompasses proteins hitherto dismissed as inhibin-like or inhibin-related proteins.

FSH in testes of marmosets during development: immunocytochemical localization and de novo biosynthesis

Immunocytochemical localization of FSH was carried out in various cell types of marmoset testes during development using antisera generated against intact as well as beta-subunit of human FSH. Significant differences in the intensity as well as distribution of FSH in various cell types were observed in neonatal, pubertal, and adult marmosets. Intensity of staining in Leydig cells was maximum at day 1 and in adults (1-3 years), whereas it was minimum at 3 months. In seminiferous tubules (Sertoli cells), FSH was present in trace amount until puberty and subsequently increased at maturity. Further studies demonstrate de novo biosynthesis of FSH-like moiety in vitro by testicular tissue, which was age dependent.

Inhibin-like and gonadotropin-like immunoreactivity in pituitary cells of male monkeys (Macaca fascicularis, Macaca mulatta)

Inhibin-like immunoreactivity was detected by immunocytochemistry in the pituitaries of untreated male crab-eating macaques (cynomolgus monkey) and rhesus monkeys, in rhesus monkeys actively immunized against FSH, and in one orchidectomized crab-eating macaque. Localizations were performed by the immunogold-silver staining with 5-nm colloidal gold-conjugated second or third antibodies and by the alkaline phosphatase-anti-alkaline-phosphatase technique. Two different inhibin-specific antisera, raised against the alpha-subunit or the entire inhibin molecule, provided identical staining patterns. Positive label was confined to the pars distalis of the pituitary and occurred exclusively in the cytoplasm of morphologically different cell types throughout the pars distalis in all pituitaries. Staining was most prominent in clusters of chromophobic cells. The presence of inhibin-like activity in the pituitary of an orchidectomized monkey with undetectable serum inhibin levels suggests that inhibin is produced within the pituitary gland. Co-localization studies for the beta-subunits of the gonadotropic hormones revealed that on average 82% of the gonadotropes were bihormonal. Using the same protocol, co-localization of inhibin-like activity with gonadotropin-like immunoreactivity revealed only a small degree of common distribution (less than 15%). Inhibin-positive cells were frequently in close proximity to gonadotropic cells and, thus, paracrine effects of inhibin on gonadotropin-synthesizing cells are conceivable.

Occurrence of bioactive and immunoreactive inhibin (13 KD) in human epididymis

Using specific polyclonal antibodies generated against a 13 KD human testicular inhibin, immunocytochemical localization of inhibin was carried out in different regions of human epididymis. The concentrations of inhibin were greater in caput and corpus regions as compared to the caudal region. The epididymal inhibin was found to be bioactive, since it suppressed specifically the FSH levels of rat pituitaries in vitro. Spermiophage/macrophage cells exhibited strong staining for inhibin which were suggestive of a possible role of inhibin in modulation of immune function. In view of the known activities of inhibin in cellular growth, differentiation, and steroidogenesis, epididymal inhibin could have a role in acquisition of sperm fertilizing capabilities.

Cellular distribution of inhibin in marmoset testes during development

Using polyclonal antibodies against a 13 KD human testicular inhibin, immunocytochemical localization studies were carried out in marmoset monkey testes. The pattern as well as the intensity of immunocytochemical staining for inhibin vary substantially during development. In early development (day 1 to 2 months) Leydig cells are the predominant cell types showing intense staining which reaches its nadir at 3 months. Subsequently both Sertoli cells as well as Leydig cells show equal intensity of inhibin staining. Testicular inhibin is likely to play a vital role in cell to cell communication.