Inhibin is an important factor in the regulation of FSH secretion in the adult male hamster

We investigated the importance of inhibin and testosterone in the regulatio n of gonadotropin secretion in adult male golden hamsters (Mesocricetus aur atus). After castration, plasma concentrations of inhibin and testosterone were reduced to undetectable, whereas plasma follicle-stimulating hormone ( FSH) and luteinizing hormone (LH) were increased. After hemicastration, pla sma FSH and LH increased moderately and plasma inhibin decreased to one-hal f its initial level. Plasma testosterone levels in hemicastrated animals de creased 3 h after hemicastration but returned to those in sham-operated ani mals at 6 h, Plasma LH in the castrated hamster declined comparably to inta ct animals with testosterone treatment; plasma FSH also decreased but still remained at levels higher than those in intact animals. After treatment wi th inhibin in long-term-castrated animals, plasma FSH decreased, whereas pl asma LH was not altered. Intact males treated with flutamide, an anti-andro gen, showed a significant increase in plasma LH but not in FSH. On the othe r hand, treatment with anti-inhibin serum induced a significant elevation i n plasma FSH, but not in LH. Using immunohistochemistry, we showed that the inhibin alpha-subunit was localized to both Sertoli and Leydig cells. The present study in adult male hamsters indicates that FSH secretion is regula ted mainly by inhibin, presumably from Sertoli and Leydig cells, and that L H secretion is controlled primarily by androgens produced from the Leydig c ells. This situation is more similar to that of primates than of rats.