Cardiovascular effects of intracerebroventricular injection of dopamine after selective MAO inhibition in rats.

Intracerebroventricular injection of dopamine (30-300 micrograms) caused a dose-dependent reduction in the blood pressure and cardiac rate of anaesthetized rats. Inhibition of MAO-type A with clorgyline enhanced the vasodepressant effect while it reversed the bradycardiac effect. Deprenyl, a MAO-type B inhibitor, did not modify the cardiovascular effects of dopamine injected into the cerebral ventricles. The persistent hypotensive action of dopamine in clorgyline-pretreated rats was abolished by the central blockade of alpha-adrenoreceptors with intracerebroventricular injection of phentolamine, whereas haloperidol given by the same route did not affect the hypotensive response. The results suggest that dopamine centrally affects cardiovascular regulation, either after conversion into noradrenaline, or through a direct stimulation of central alpha-adrenoceptors.