Dopamine and temperature regulation in the primate: effects of apomorphine and pimozide

The purpose of this study was to determine the effects of a specific dopamine-receptor agonist (apomorphine) and antagonist (pimozide) on temperature regulation in the primate. Using 4 rhesus monkeys and 2 patas monkeys as subjects, increasing doses of apomorphine (0.05, 0.1, 0.2, 0.4, 0.6 mg/kg) injected subcutaneously produced a dose-dependent hypothermia associated with sharp elevations in tail-skin and ear pinna temperatures. Apomorphine also produced dose-related behavioral responses including salivation, hypermotility, hypersensitivity, pupil dilation and erection, suggesting a central site of action. Pre-treatment with pimozide (0.5 mg/kg, SC) blocked the apomorphine-induced hypothermia, but the subcutaneous injection of pimozide alone had no effect on body temperatures. In the patas monkey, the decline in colonic temperature following the injection of apomorphine (0.4 mg/kg) was not associated with a change in metabolic rate or heart rate. In 2 animals, mean colonic temperature fell 1.7, 0.67, and 0.3 degrees C following the injection of apomorphine ((0.4 mg/kg) in 15, 25, and 35 degrees C environments, respectively. These data suggest that the apomorphine-induced hypothermia was mediated by an increase in heat dissipation rather than a decline in heat production. The site of this drug remains to be elucidated.