Oxytocin and vasopressin secretion in monkeys administered apomorphine and a D2 receptor agonist

Nauseogenic agents, such as apomorphine, were previously reported to promote peripheral release of oxytocin (OT), but not vasopressin (AVP) in rats, and AVP, but not OT in humans (7-13). In the present study, we compared the peripheral secretory responses of OT and AVP in adult male and female rhesus and male cynomolgus monkeys administered graded doses of apomorphine and the respective dopamine D1 and D2 receptor agonists, CY 208-243 and LY 163502. Apomorphine (50-400 micrograms/kg) and LY 163502 (10-100 micrograms/kg) elicited dose-dependent stimulation of OT and AVP, whereas CY 208-243 did not significantly increase secretion of either hormone. The magnitude of the OT and AVP secretory response varied among the animals. Peripheral OT and AVP responses were robust, but the magnitude of the secretory responses was greater for AVP than OT. None of the animals displayed emetic behavior during the studies. These studies indicate that dopaminergic stimulation, particularly of D2 receptors, can regulate both AVP and OT secretion in monkeys.