EFFECT OF LUTEINIZING-HORMONE-RELEASING HORMONE ANALOGS ON THE RAT OVARIAN FOLLICLE DEVELOPMENT

Our objective was to study the direct action of luteinizing hormone-re leasing hormone (LHRH) agonist buserelin and LHRH antagonist Cetroreli x (SB-75) on cell proliferation and differentiation in the rat ovarian follicle, Preovulatory follicles were isolated from PMSG-primed immat ure rats and incubated in the presence or absence of hCG (10 IU/ml), b userelin (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 vesi cle breakdown at 10(-6) M buserelin (73.3%) did not differ from that o f hCG-treated control (73.3%), Buserelin also significantly stimulated prostaglandin E-2 and progesterone production by follicles, but not e stradiol production, Granulosa cells were obtained from the preovulato ry follicles and cultured for 5 days, Epidermal growth factor (EGF) st imulated granulosa cell growth at concentrations of 1, 10 and 100 ng/m l, In contrast, both buserelin and Cetrorelix inhibited granulosa cell growth dose-dependently in the range of 10(-10)-10(-5) M, with Cetror elix inducing a greater growth inhibition than buserelin, Electrophore tic analysis of genomic DNA extracted from granulosa cells treated wit h 10(-6) M concentration of either LHRH analog revealed a definitive l adder pattern of oligonucleosomal length DNA fragments characteristic of apoptosis, Western blotting detected that EGF-induced tyrosine phos phorylation was not affected by either analog, These results demonstra te that LHRH agonist and antagonist inhibit directly proliferation of granulosa cells through apoptosis, without interference with EGF recep tor phosphorylation whereas LHRH agonist stimulates cell differentiati on in the preovulatory follicle.