EFFECTS OF GONADOTROPIN-RELEASING-HORMONE AGONIST ON STEROIDOGENESIS IN THE RAT OVARY

To assess the regulatory roles of gonadotropin-releasing hormone (GnRH ) in ovarian function, the kinetics of the ovarian GnRH receptor and t he effects of the GnRH superagonist buserelin on steroidogenesis in ov arian cell culture were examined. Scatchard analysis of buserelin-bind ing to crude ovarian cell membrane revealed a specific high-affinity G nRH receptor. Buserelin together with follicle-stimulating hormone sti mulated estradiol (E(2)) production in immature follicles in hypophyse ctomized and DES-treated rats. On the other hand, applied to developin g follicles of rats treated with pregnant-mare-serum gonadotropin buse relin suppressed E(2) production to terminate follicle maturation and simultaneously stimulated progesterone (P-4) production to induce lute inization. With ovarian cells luteinized by human chorionic gonadotrop in in vitro, buserelin suppressed production of both P-4 and E(2), lea ding to luteolysis. Buserelin affected steroid production by modulatin g activities of key enzymes in steroid synthesis. These findings indic ate that buserelin action depended on the gonadotropin priming of ovar ian cells, and suggest the possible involvement of GnRH in the regulat ion of steroidogenesis throughout the ovulatory cycle.