Regulation of ovarian follicle differentiation in gonadotrophin-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 rats 48 h after administration of pregnant mare's serum gonadotrophin alone (granulosa cells) or followed by human chorionic gonadotrophin (luteal cells). Isolated granulosa cells were cultured in serum-free medium, different stimuli added for periods of 48 h, and 3H-thymidine incorporation was measured. Both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) inhibited 3H-thymidine incorporation by cultured 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 found to stimulate 3H-thymidine incorporation in granulosa cells (Estradiol: 5, 50, 500 ng/mL = 17, 37, 76% stimulation, respectively). In luteal cells, the rate of basal 3H-thymidine incorporation was very low (granulosa cells: 2560 +/- 310; luteal cells: 661 +/- 92 cpm/100,000 cells) and not modified by any stimulus. To determine the possible production of an inhibitory growth factor by the early corpus luteum, 3H-thymidine 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 3H-thymidine incorporation was observed (74 and 76% of inhibition, respectively). Results suggest that an inhibitory growth factor produced by luteal cells after luteinizing gonadotrophin stimulus could be involved in the differentiation of growing follicles to corpus luteum.