The role of inhibin in adult male rats: the effect of inhibin deficiency and androgen antagonism on serum and pituitary gonadotrophins.

We examined the ability of inhibin-F contained in porcine follicular fluid (pFF) to regulate serum gonadotrophins in male rats made deficient in endogenous inhibin and unable to respond to normal endogenous androgen levels. Efferent duct ligation (EDL) effected endogenous inhibin deficiency and the anti-androgen flutamide (F) (13.4 mg/dose, sc once per day) raised the set point for androgen control of the hypothalamus to a level intermediate between the intact and castrate serum gonadotrophin levels. EDL, F and EDL + F caused serum FSH levels to rise and administration of pFF (2 ml per day) suppressed the elevated serum FSH levels of these experimental models to intact animal levels. Though EDL had no effect on serum LH, F increased the serum LH levels and EDL plus F increased them further. Treatment with pFF suppressed the serum LH to intact levels. EDL rats had slightly increased serum androgen (6 ng/ml) but F and EDL + F treated rats had very greatly increased serum androgen concentrations (22 and 32 ng/ml, respectively) which treatment with pFF suppressed to intact levels. Pituitary FSH was increased by EDL and LH was increased by F. In both cases, the increased pituitary gonadotrophins were suppressed by treatment with pFF. We conclude that inhibin regulates synthesis and secretion of FSH and secretion of LH.