Cardiovascular adrenergic activity of dopamine in the dog

Abstract

In previous studies, dopamine infused at low doses in intact dogs has exerted an inotropic effect without change in systemic blood pressure. This was in contrast to the action of isoproterenol, a pure β-adrenergic agent with which a lowering of mean blood pressure usually accompanies the inotropic effect. This difference suggested that even at lower doses dopamine possessed α-adrenergic properties which were undetectable as a pressor response. The present study was conducted to demonstrate such α activity and to evaluate its effects upon left ventricular performance following β-adrenergic blockade. The results confirm that dopamine in low infusion doses does prossess α-adrenergic activity. Such activity was essentially masked during dopamine infusion alone, but was uncovered in the presence of β-adrenergic blockade. Possibly of greater significance, these data indicate that the intact canine left ventricle, while preserving a relatively steady state of isovolumic contractility, may be unable to maintain stroke volume in the face of increased ejection resistance during propranolol-induced β-adrenergic blockade.