Pituitary adenylate cyclase activating polypeptide (PACAP) functions as a novel growth hormone (Gh) releasing factor in the goldfish

In this study, the role of PACAP in regulating GH release in the goldfish was investigated. PACAPs, including zebra fish PACAPs, frog PACAP38, and ovine PACAPs (PACAP38 and PACAP27), stimulated GH release from perifused goldfish pituitary cells in a dose-dependent manner. The GH-releasing effect of PACAP38 was seasonal, with the highest GH response in prespawning fish, intermediate in recrudescent fish, and the lowest in sexually regressed fish. PACAP38-induced GPI release was additive to the GH-releasing action of salmon gonadotropin-releasing hormone (GnRH), but was inhibited by somatostatin, serotonin, and norepinephrine. The GH response to PACAP38 was also suppressed by the protein kinase A (PKA) inhibitor H89 or by the voltage-sensitive Ca2+ channel (VSCC) blockers, including nifedipine and verapamil. These results, as a whole, suggest that PACAP is a part of the neuroendocrine system regulating GH release in the goldfish. The GH-releasing action of PACAP is probably mediated through the cAMP/PKA cascade and Gaze entry through VSCC.