REGULATION OF OVARIAN FOLLICLE DIFFERENTIATION IN GONADOTROPIN-STIMULATED RATS

The aim of the present study was to investigate the regulation of the in vitro DNA synthesis of ovarian cells recovered from prepubertal rat s 48 h after administration of pregnant mare's serum gonadotrophin ato ne (granulosa cells) or followed by human chorionic gonadotrophin (lut eal cells). Isolated granulosa cells were cultured in serum-free mediu m, different stimuli added for periods of 48 h, and H-3-thymidine inco rporation was measured. Both follicle-stimulating hormone (FSH) and lu teinizing hormone (LH) inhibited H-3-thymidine incorporation by cultur ed granulosa cells in a dose-dependent manner (FSH: 10, 100, 200 ng/mL = 26, 41, 49% inhibition, respectively; LH: 0.1, 1, 10 ng/mL = 11, 37 , 75% inhibition, respectively). On the other hand, estradiol was foun d to stimulate H-3-thymidine incorporation in granulosa cells (Estradi ol: 5, 50, 500 ng/mL = 17, 37, 76% stimulation, respectively). in lute al cells, the rate of basal H-3-thymidine incorporation was very low ( granulosa cells: 2560 +/- 310; luteal cells: 661 +/- 92 cpm/100,000 ce lls) and not modified by any stimulus. To determine the possible produ ction of an inhibitory growth factor by the early corpus luteum, H-3-t hymidine incorporation by granulosa cells was assessed in the presence of 10% conditioned media (CM) recovered from luteal cell cultures. A marked inhibition both in basal and estradiol-stimulated H-3-thymidine incorporation was observed (74 and 76% of inhibition, respectively). Results suggest that an inhibitory growth factor produced by luteal ce lls after luteinizing gonadotrophin stimulus could be involved in the differentiation of growing follicles to corpus luteum.