REGULATION OF GONADOTROPIN-SECRETION BY INHIBIN, TESTOSTERONE AND GONADOTROPIN-RELEASING-HORMONE IN PITUITARY CELL-CULTURES OF MALE MONKEYS

The effects of bovine inhibin, testosterone and GnRH on gonadotrophin secretion by primate pituitary cells were characterized in vitro using pituitaries from six male rhesus monkeys and one male cynomolgus monk ey. The effect of inhibin on basal secretion of FSH and LH was investi gated. Dose-response curves in monkeys and rats were compared. GnRH do se-response curves in the presence and absence of testosterone were al so examined in monkeys. In monkey pituitary cells, testosterone at a c oncentration of 10(-7) M had no effect on LH or FSH secretion. Inhibin suppressed FSH secretion to 50.8% of that of controls with no effect on LH. In rats, FSH secretion was suppressed to 50.8% of that of contr ols with a median effective dose (ED50, 95% range) of 1.298 (1.064-1.5 84) U/ml, compared with 1.024 (0.7204-1.455) U/ml in monkeys. In monke y pituitary cells, LH release was stimulated 9.9-fold and FSH 3.3-fold by GnRH. Testosterone had no effect on basal or GnRH-stimulated gonad otrophin release. These results support the view that the pituitary is not the target organ for the negative feedback action of testosterone in the male. In vitro, inhibin is the major regulator of FSH secretio n at the pituitary level.