Chicken gonadotropin-releasing hormone II increases plasma catecholamines in the bullfrog

The aim of the present experiments was to test the effects of two native neuropeptides, [His⁵, Trp⁷, Tyr⁸]gonadotropin-releasing hormone (chicken GnRH II) and [Trp⁷, Leu⁸]GnRH (salmon GnRH), on the sympathoadrenal system of chronically cannulated, conscious bullfrogs (Rana catesbeiana). We observed that i.v. injection of chicken GnRH II or salmon GnRH increased plasma noradrenaline and adrenaline concentrations, at doses that did not significantly affect arterial blood pressure or heart rate. Chicken GnRH II was 10 times more potent than salmon GnRH for increasing plasma adrenaline, while the two neuropeptides were equally effective in raising noradrenaline concentration. These observations are consistent with a regulatory role for chicken GnRH II in the bullfrog sympathoadrenal system.