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 goldfish. DA stimulated GH release from perifused pituitary fragments of goldfish in a dose-dependent manner. The GH-releasing effect of DA was seasonal, being the highest in sexually regressed fish, intermediate in recrudescent 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 non-selective DA agonist, also increased the plasma GH levels and enhanced the linear body growth of goldfish. These results strongly suggest that DA, by acting through DA D1 receptors, functions as a GH-releasing factor in the goldfish.