Responses of the canine hepatic arterial and portal venous vascular beds to dopamine.

Dopamine was injected in graded doses into the hepatic artery of the anaesthetized dog: the typical response was an initial vasoconstriction followed by a more protracted vasodilatation. The vasodilatation was unaffected by propranolol, but was antagonized by haloperidol. The initial hepatic arterial vasoconstriction was inhibited both by haloperidol and by phentolamine. The experiments suggest that the initial vasoconstriction was due to alpha-adrenoceptor stimulation and that the secondary vasodilatation was the result of the stimulation of dopamine receptors. In separate experiments, dopamine was injected into the hepatic portal vein of the dog. The only response seen was a dose-dependent portal vasoconstriction which was antagonized both by haloperidol and by phentolamine. Since both of these antagonists attenuated the portal vasoconstrictor effects of intraportal phenylephrine, it is probable that the portal vasoconstriction effect of dopamine is due to alpha-adrenoceptor stimulation.