Male and Female Inhibin

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Abstract
The testis and ovary secrete a nonsteroidal hormone that selectively inhibits pituitary FSH secretion. Inhibin, a polypeptide hormone produced by Sertoli cells in the seminiferous tubules and by the granulosa cells of the ovarian follicle, is isolated from seminal fluid, rete testis fluid testicular and ovarian extracts, and follicular fluid. There may be two forms of inhibin, a form of higher molecular weight (> 10,000 daltons) being the precursor of a low-molecular-weight form (> 5,000 daltons). The functional integrity of inhibin is destroyed by trypsin or pepsin digestion and exposure to heat. This induces the formation of antibodies that are able to neutralize endogenous inhibin when injected into adult males or females. Apart from its main action at the pituitary level, inhibin could also function at the hypothalamus or directly at the gonad. Inhibin inhibits the release of FSH and to a lesser extent of LH induced by exogenous GnRH in vivo and in vitro. Inhibin reduces the endogenous GnRH content of hypothalami maintained in organ culture. These reactions have been utilized in the development of in vivo and in vitro assay methods. It is feasible that inhibin is involved in the regulation of the ovarian cycle, and that this hormone plays a more important role in the feedback regulation of FSH in the adult female than in the adult male.