The present study was undertaken to investigate the possible involvement of prostanoids in the inhibitory effect of endothelin-1 (ET-1) on progesterone production of ovarian granulosa cells. ET-1 (1 x 10(-7) M) decreased the basal and follicle-stimulating hormone- (FSH) stimulated progesterone production from both human and porcine granulosa cells. Indomethacin dose-dependently inhibited progesterone release, but did not alter the inhibitory effect of ET-1 (1 x 10(-7) M) on progesterone production of cultured ovarian granulosa cells. This study shows that ET-1 suppresses basal and FSH-stimulated progesterone production by ovarian granulosa cells, but this effect is not mediated by prostanoids.