Interactions of somatostatin, gonadotropin-releasing hormone, and the gonads on dopamine-stimulated growth hormone release in the goldfish

Abstract

Previously, we have demonstrated that dopamine (DA) stimulates growth hormone (GH) release from the goldfish pituitary through DA D1 receptors. In the present study, the role of DA as a GH-releasing factor was further examined in vitro by studying its interactions with other GH regulators in the goldfish. The GH-releasing effects of DA and salmon gonadotropin- releasing hormone (sGnRH) were found to be independent and additive at the pituitary cell level. Both the kinetics and the magnitude of DA-stimulated GH release were unaffected by simultaneous treatment with sGnRH and vice versa. Castration of sexually mature (or prespawning) goldfish significantly enhanced the DA-stimulated GH release, but at the same time reduced the GH responses to sGnRH. Furthermore, the GH responses to DA and the D1 agonist SKF38393 were totally abolished by somatostatin (SRIF), a known GH release inhibitor in the goldfish. These findings strongly indicate that SRIF, DA, sGnRH, and gonadal factors interact at the pituitary level to regulate GH release in the goldfish.