Inhibition of estradiol-induced gonadotropin release in ovariectomized rhesus macaques by a gonadotropin-releasing hormone antagonist.

Six adult ovariectomized rhesus macaques were given a gonadotropin-releasing hormone (GnRH) antagonist [Ac-beta-(2)DNAL,pFDPhe,DTrp,DArg]-GnRH, by intravenous infusion for 3 to 3.5 days to determine whether the positive feedback action of estradiol benzoate (E2B) on pituitary luteinizing hormone (LH) secretion could be inhibited by blockage of GnRH binding to pituitary gonadotropes. The LH release was suppressed when the antagonist was given either as a bolus injection every 6 hours or as a constant infusion, beginning 24 hours after the E2B was administered. Both LH release and follicle-stimulating hormone release were suppressed if the GnRH antagonist infusion began when the E2B was administered. The results suggest that continued hypothalamic GnRH stimulation of the pituitary is necessary for the full expression of the preovulatory-like gonadotropin surge that occurs in ovariectomized macaques in response to E2.