CARDIOVASCULAR EFFECTS OF DOPAMINE AFTER CENTRAL ADMINISTRATION INTO CONSCIOUS CATS

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Abstract
Dopamine (30 and 45 μg) administered intracerebroventricularly (i.c.v.) to a group of 10 conscious normotensive cats caused dose‐related increases in blood pressure and heart rate. In 4 of these animals the initial cardiovascular stimulant effects of i.c.v. dopamine were followed by hypotension and bradycardia. α‐Methyldopamine (30 and 45 μg i.c.v.) produced qualitatively similar responses to dopamine except that the cardiovascular stimulant effects were smaller and the secondary depressant effects somewhat more prolonged. Both stimulant and depressant effects of i.c.v. dopamine and α‐methyldopamine were greatly inhibited by autonomic ganglion blockade or by adrenergic neurone blockade. The cardiovascular stimulant effects of both i.c.v. dopamine and i.c.v. α‐methyldopamine were selectively inhibited by β‐adrenoceptor blocking agents whilst the cardiovascular depressant effects of these substances were abolished by the α‐adrenoceptor blocker phentolamine or by the dopamine‐β‐hydroxylase inhibitor disulfiram. Haloperidol by either i.c.v. or the intravenous route abolished both cardiovascular stimulant and depressant effects of i.c.v. dopamine, whilst pimozide by either route inhibited only the cardiovascular stimulant effects. In 2 cats, injection of dopamine into the cisterna magna produced predominantly depressant effects on the cardiovascular system except with a higher dose which induced biphasic responses.