Prostaglandin-independent anovulatory mechanism of indomethacin action: Inhibition of tumor necrosis factor alpha-induced sheep ovarian cell apoptosis

Indomethacin, a nonsteroidal anti-inflammatory agent, is a potent inhibitor of ovulation in vertebrates. The presumptive ob ligate anovulatory mode of indomethacin action is via suppression of ovarian prostaglandin production . We report that a very high systemic dose of indomethacin (800 mg i.m.) is required to block ovulation in gonadotropin-treated anestrous ewes, A lowe r dose of indomethacin (200 mg), which negated the preovulatory rise in fol licular prostaglandin (PGF(2 alpha)) biosynthesis, did not prevent ovulatio n, Endothelial secretion of tumor necrosis factor (TNF)-alpha within the ap ical follicular wall (prospective site of rupture) was not altered by indom ethacin; notwithstanding, the apoptosis (DNA-fragmentation)-inducing effect of TNF-alpha (a determinant of ovulatory stigma formation) was attenuated by 800 (but not 200) mg indomethacin, A suprapharmacological concentration of indomethacin also was necessary to protect ovarian surface epithelial ce lls from a (prostaglandin-independent) cytotoxic effect of TNF-alpha in vit ro. It is concluded that indomethacin inhibits ovulation by anti-apoptotic mechanisms that can be dissociated from the paradigm of prostanoid down-reg ulation.