Anti-ovulatory effects of RU486 and trilostane involve impaired cyclooxygenase-2 expression and mitotic activity of follicular granulosa cells in rats

To explore the mechanism for anti-ovulatory effects of blockade of preovulatory synthesis and action of progesterone, we focused on cyclooxygenase (COX)-2 induction and mitotic activity of granulosa cells in gonadotropins-treated rats. Treatment with RU486 (a progesterone receptor antagonist) or trilostane (a 3β-hydroxysteroid dehydrogenase inhibitor) just prior to or 4 h after human chorinonic gonadotropin (hCG) (hCG4h) decreased ovulation rates and circulating progesterone level. Human CG induction of immunoreactive COX-2 in the granulosa layer of mature Graafian follicles at hCG8h was reduced by RU486 treatment at hCG0h and trilostane treatment at hCG4h. RU486 treatment further attenuated ovarian prostaglandin E2 (PGE2) level significantly. Cell proliferative activity in mural granulosa layer of the inhibitors-treated follicles was significantly lower than in intact group. Obtained results show that inhibition of synthesis and action of progesterone caused attenuated COX-2/PGE2 system and dysregulated mitotic response of granulosa cells, resulting in decreased ovulation.

► Anti-ovulatory effects of RU486 and trilostane were evaluated in rats.
► The drugs inhibit hCG-induced progesterone synthesis and ovulation.
► They attenuate hCG-induced COX-2 expression in follicular granulosa cells.
► RU486 significantly blocks the rise in ovarian PGE2 content.
► They further inhibit mitotic activity of granulosa cells.