DOPAMINE FUNCTIONS AS A GROWTH HORMONE-RELEASING FACTOR IN THE GOLDFISH, CARASSIUS-AURATUS

In vivo and in vitro approaches have been used to examine the role of dopamine (DA) as a growth hormone (GH)-releasing factor in the goldfis h. DA stimulated GH release from perifused pituitary fragments of gold fish in a dose-dependent manner. The GH-releasing effect of DA was sea sonal, being the highest in sexually regressed fish, intermediate in r ecrudescent fish, and the lowest in sexually mature (prespawning) fish . The GH response to DA was blocked by the D1 antagonist (+)SCH23390, confirming the involvement of D1 receptors in DA-stimulated GH release . In studies using static incubation of pituitary cells, somatostatin, a known physiological GH-release inhibitor in the goldfish, abolished the GH response to DA. Intraperitoneal injection of apomorphine, a no n-selective DA agonist, also increased the plasma GH levels and enhanc e the linear body growth of goldfish. These results strongly suggest t hat DA, by acting through DA D1 receptors, functions as a GH-releasing factor in the goldfish.