ACUTE EFFECTS OF PROSTAGLANDIN-F(2-ALPHA), LUTEINIZING-HORMONE, AND ESTRADIOL ON 2ND MESSENGER SYSTEMS AND ON THE SECRETION OF OXYTOCIN ANDPROGESTERONE FROM GRANULOSA AND EARLY LUTEAL CELLS OF THE EWE

Previous reports have suggested that gonadotropins, estradiol, and pro staglandin F2alpha (PGF2alpha) have varying effects on progesterone an d oxytocin synthesis or secretion in cultured granulosa and luteal cel ls collected at different stages of the estrous cycle. The experiments reported here were designed to investigate whether effects of these a gonists on secretion of hormones and their coupling to second messenge r systems changed around the time of ovulation. Granulosa cells and Da y 2 luteal cells of the ewe were cultured for three days and then trea ted for 30 min with varying doses of PGF2alpha, LH, or estradiol. LH i ncreased intracellular cAMP at both stages, but granulosa cells were m ore responsive in terms of both minimum effective dose (10 compared wi th 100 ng/ml) and degree of stimulation. LH caused no change in intrac ellular inositol phosphate levels. Both granulosa and early luteal cel ls responded to LH treatment by an increase in progesterone output in a dose-responsive fashion. PGF2alpha increased inositol phosphate accu mulation in cells collected at both stages of the cycle. All doses tes ted (10(-6)-10(-8) M) stimulated the release of oxytocin into the cult ure medium from both granulosa and luteal cells. Progesterone secretio n was also increased, but only at the highest dose (10(-6) M). Estradi ol treatment (10(-6) M) did not affect either the inositol phosphate o r cAMP second messenger systems, but it did inhibit the secretion of o xytocin from granulosa cells. It is concluded that PGF2alpha stimulate s oxytocin secretion in vitro via activation of the inositol phosphate /Ca2+ second messenger pathway, and that LH increases progesterone syn thesis acting via cAMP in both luteinized granulosa and early luteal c ells, whereas estradiol does not work through either of these pathways . These data suggest that previously reported changes in the chronic e ffects of gonadotropins, PGF2alpha, and estradiol on oxytocin synthesi s during the periovulatory period cannot be explained in terms of acti vation of alternative signalling pathways. The short-term stimulatory effects of PGF2alpha on progesterone output differ from its reported i nhibitory effect in the mature ovine CL and support the idea that gran ulosa/luteal cell responsiveness to the same agonists alters during lu teal development.