Dopaminergic stimulation of oxytocin concentrations in the plasma of male and female monkeys by apomorphine and a D2 receptor agonist.

Administration of the dopamine receptor agonist apomorphine causes a dose-dependent increase in plasma oxytocin concentrations and dose-specific behavioral changes in rodents. To investigate whether dopamine receptor agonists will elicit similar neuroendocrine and behavioral effects in primates, we administered graded doses of apomorphine and the respective dopamine D1 and D2 receptor agonists, CY 208-243 and LY 163502, to monkeys and monitored plasma concentrations of oxytocin and behavior. Five female rhesus, two male rhesus, and two male cynomolgus monkeys had chronic indwelling venous catheters implanted and were maintained on standard jacket/tether/swivel systems to allow remote blood sample collection. During experiments, blood samples were collected 10 and 5 min before drug injection and at 2- to 120-min intervals after each injection. Apomorphine (50-400 micrograms/kg) and LY 163502 (10-100 micrograms/kg) elicited dose-dependent stimulations of oxytocin secretion. CY 208-243 (100-400 micrograms/kg) did not significantly affect oxytocin secretion. Low doses of apomorphine (50-100 micrograms/kg) and LY 163502 (10-25 micrograms/kg) elicited yawning, and high doses of apomorphine (200-400 micrograms/kg) and LY 163502 (50-100 micrograms/kg) elicited stereotypic behaviors. No behavioral effects of CY 208-243 (100-400 micrograms/kg) were observed. The magnitude of the oxytocin secretory responses varied among animals, but was similar in male and female monkeys. In summary, apomorphine and LY 163502 both elicited dose-related stimulation of oxytocin secretion coupled with dose-specific behavioral changes in male and female monkeys, while no effects of CY 208-243 on these parameters were observed. We conclude that dopamine receptor agonists, and in particular D2 agonists, may be useful tools for studies exploring the physiological and behavioral actions of oxytocin in primates.