Effects of dopamine on gonadotropin release in female goldfish, Carassius auratus.

Intraperitoneal injections of dopamine (DA) or its agonist, apomorphine decreased and pimozide, a DA antagonist, increased serum gonadotropin (GtH) levels in normal female goldfish. Injection of DA into the third cranial ventricular did not alter serum GtH concentrations. Intraperitoneal injections of DA or apomorphine each reduced the highly elevated serum GtH levels caused by preoptic lesions which abolish an inhibitory hypothalamic influence on GtH release allowing prolonged spontaneous release of GtH. Intraperitoneal injections of DA or apomorphine blocked the stimulation of GtH release induced by injections of a luteinizing hormone-releasing hormone analogue. These results indicate that DA has GtH release-inhibitory activity by actions directly on gonadotrophs to inhibit spontaneous secretion of GtH, and by blocking the actions of the GtH-releasing hormone.