Inhibin, a member of a new peptide family.

There is considerable experimental evidence that follicle stimulating hormone (FSH) and luteinizing hormone (LH) are regulated by separate mechanisms in some circumstances. Part of this differential regulation involves the gonadal factor inhibin, which preferentially affects FSH. A sensitive and specific bioassay based on suppression of FSH cell content in dispersed cultured pituitary cells was used to monitor the purification of inhibin to homogeneity. The two subunits were cloned and the full amino acid sequence of the molecule established. Much evidence has been gathered to support the hypothesis that FSH and inhibin form a classic endocrine closed-loop feedback system in which FSH stimulates inhibin secretion both in vivo and in vitro and inhibin in turn exerts a significant suppressive effect on FSH secretion. The establishment of an inhibin radioimmunoassay has allowed the description of its concentrations in various physiological states such as in the normal menstrual cycle, during puberty and in pregnancy. Inhibin levels were shown to be within the normal range in the polycystic ovarian syndrome. A potential commercial application of inhibin is as a vaccine to increase fertility in domestic animals.