Inhibition of atresia leading to luteinization of ovarian preovulatory follicles by NS398, a specific cyclooxygenase-2 inhibitor

Most ovarian follicles degenerate in a process called atresia, but the precise mechanisms behind this process remain unclear. We have investigated the roles of cyclooxygenase-2 and prostaglandin E2 in the atresia of preovulatory follicles in immature rats primed with pregnant mare's serum gonadotropin. Massive atresia was histologically confirmed to occur in preovulatory follicles of control rats. In contrast, administration of NS398, a specific cyclooxygenase-2 inhibitor, caused luteinization resulting in development of apparently normal corpora lutea and also atypical membranous corpora lutea. Progesterone secretion was high in the plasma of these rats, indicating that the corpora lutea were functional. These data suggest that cyclooxygenase-2 may be involved in determining whether the fate of preovulatory follicles will be atresia or luteinization.