Dopamine involvement in the regulation of gonadotropin secretion in coho salmon

The effects of intraperitoneal injections of [D-Ala 6 ,Pro 9 -N-ethylamide]-luteinizing hormone-releasing hormone (LHRH-A) and pimozide, a dopamine receptor antagonist, on plasma gonadotropin levels and ovulation in coho salmon were investigated. Both LHRH-A (0.02 mg/kg body weight) and pimozide (10 mg/kg body weight) stimulate gonadotropin secretion, with LHRH-A causing a more rapid onset of gonadotropin release and a higher magnitude increase in plasma gonadotropin levels than pimozide. Pimozide caused a marked potentiation of the gonadotropin release response to LHRH-A. Injections of LHRH-A alone and in combination with pimozide were effective means of inducing ovulation, whereas pimozide alone was ineffective. These data support the concept that dopamine participates in the regulation of gonadotropin secretion in teleosts and suggest that dopamine has a minor role in the regulation of ovulatory gonadotropin changes in coho salmon compared with cyprinids.