Induction of ovulation by endothelin-3 in rats

Endothelins vary in their biological activity. We therefore examined the effects of endothelin-3 (ET-3) on ovulation and secretion of LH, FSH and prolactin in rats in which naturally occurring ovulation was blocked by the administration of sodium pentobarbital (40 mg/kg, i.p.) prior to the critical period (1330 h) on the day of pro-oestrus. ET-3 (10 nmol/kg) was given via the jugular vein under pentobarbital anaesthesia from 1600 to 1800 h on the day of pro-oestrous and induced ovulation in all rats whether given by venous injection or by infusion but the number of ova in rats injected with ET-3 was less than that in normally cycling control rats. Infusion of ET-3 stimulated the secretion of LH but caused a lower than expected rate of secretion of FSH. It would therefore appear that ET-3 causes release of the total amount of LH that is required for induction of ovulation. Our findings strongly suggest that ET-3 has a physiologically significant role in the regulation of anterior pituitary hormone secretion.