THE MODULATION OF FOLLICLE-STIMULATING HORMONE-INDUCED AROMATASE ACTIVITY BY PROGESTINS IN PORCINE GRANULOSA CELLS IN VITRO

Abstract

The nature and mechanism by which progestins modulate the induction of aromatase activity by FSH was examined. Granulosa cells were first isolated from non-atretic medium sized follicles of prepubertal pigs. They were cultured for an initial 48 h induction period, during which FSH and other chemicals to be tested for their effects on the induction of aromatase activity were added. After induction, the cells were cultured for a further 6 h test period in the presence of testosterone. The accumulation of estradiol during the test period, as measured by RIA, is taken as an index of aromatase activity. Of all three progestins tested, progesterone was found to be the most potent inhibitor of aromatase activity induced by FSH. Moreover, the inhibitory effect of 25-0H cholesterol and pregnenolone was found to be due to their conversion to progesterone. It also appears that progesterone receptors do not mediate the inhibitory effect of progesterone. Also, the induction of aromatase activity by FSH in all three stages of follicular development is enhanced by AG. Finally, it is suggested that progesterone may play an important role in the regulation of estrogen biosynthesis in granulosa cells, and hence in the selection of follicles destined for ovulation or atresia.