Effect of dopamine antagonism on the behavioral and hemodynamic responses to cocaine in piglets.

Cocaine (1.5 mg/kg i.v.) was administered to awake newborn piglets that were pretreated with either intravenous saline (placebo) or SCH23390, a dopamine antagonist, to study dopamine's role in cocaine's vascular and behavioral actions. In the placebo group, cocaine increased the locomotor activity and cerebellar and cardiac blood flow (31 +/- 36 and 72 +/- 66%), but decreased choroid plexus and renal blood flow (47 +/- 23 and 18 +/- 19%). In the SCH23390-treated group, cocaine did not affect organ blood flow or locomotor activity. Cocaine transiently increased the mean arterial blood pressure in both groups (10 +/- 7 and 18 +/- 13%). These data indicate that the behavioral and blood flow responses to cocaine in cerebellum, choroid plexus, heart, and kidneys are mediated by dopamine, whereas the arterial pressor response to cocaine is not.