Effect of luteinizing hormone-releasing hormone analogs on the rat ovarian follicle development.

Our objective was to study the direct action of luteinizing hormone-releasing hormone (LHRH) agonist buserelin and LHRH antagonist Cetrorelix (SB-75) on cell proliferation and differentiation in the rat ovarian follicle. Preovulatory follicles were isolated from PMSG-primed immature rats and incubated in the presence or absence of hCG (10 IU/ml), buserelin (10(-9)-10(-6) M) or Cetrorelix (10(-9)-10(-6) M) for 12 h in vitro. Buserelin induced meiotic maturation of the follicle-enclosed oocytes dose-dependently. The percentage of oocytes with germinal vesicle breakdown at 10(-6) M buserelin (73.3%) did not differ from that of hCG-treated control (73.3%). Buserelin also significantly stimulated prostaglandin E2 and progesterone production by follicles, but not estradiol production. Granulosa cells were obtained from the preovulatory follicles and cultured for 5 days. Epidermal growth factor (EGF) stimulated granulosa cell growth at concentrations of 1, 10 and 100 ng/ml. In contrast, both buserelin and Cetrorelix inhibited granulosa cell growth dose-dependently in the range of 10(-10)-10(-5) M, with Cetrorelix inducing a greater growth inhibition than buserelin. Electrophoretic analysis of genomic DNA extracted from granulosa cells treated with 10(-6) M concentration of either LHRH analog revealed a definitive ladder pattern of oligonucleosomal length DNA fragments characteristic of apoptosis. Western blotting detected that EGF-induced tyrosine phosphorylation was not affected by either analog. These results demonstrate that LHRH agonist and antagonist inhibit directly proliferation of granulosa cells through apoptosis, without interference with EGF receptor phosphorylation, whereas LHRH agonist stimulates cell differentiation in the preovulatory follicle.