Effects of dopamine, apomorphine gamma-hydroxybutyric acid, haloperidol and pimozide on reflex bradycardia in rats

FF Chen and MT Lin

The cardiovascular responses to i.v. doses of epinephrine were assessed in vehicle-controlled, dopamine-treated, apomorphine-treated, gamma- hydroxybutyric acid-treated, haloperidol-treated and pimozide-treated rats, under urethan anesthesia. Previous exposure to several injections of epinephrine did not change the basal values of arterial pressure and heart rate. It was found that dopaminergic transmission alterations within the brain did produce some influence on the reflex bradycardia in response to an elevation in arterial pressure. Blockade of dopaminergic receptors in brain with either haloperidol or pimozide produced a significant recution in reflex bradycardia compared to the controls. In contrast, either direct activation of central dopamine receptors witth dopamine and apomorphine or indirect activation of central dopamine receptors with gamma-hydroxybutyric acid led to an enhancement in epinephrine-induced bradycardia. The data indicate that central dopmaine systems play a role in the elaboration or modulation of reflex bradycardia. Specifically, brain dopamine appears to facilitate reflex bradycardia since activation of dopamine systems facilitated and blockade inhibited reflex bradycardia.

Volume 214, Issue 2, pp. 427-432, 08/01/1980
Copyright © 1980 by American Society for Pharmacology and Experimental Therapeutics