Role of released catecholamines in the vascular response to injected angiotensin II in the dog

The contribution of released epinephrine and norepinephrine to the pressor response induced by i.v. injected angiotensin II was assessed in pentobarbital-anesthetized dogs. Control pressor dose-response curves for i.v. angiotensin II were obtained in dogs pretreated with hexamethonium, atropine and practolol. Hexamethonium and atropine minimized the cardiovascular reflex responses elicited by the pressor action of angiotensin II which would preclude interpretation of the results. Practolol was administered to antagonize indirect cardiac stimulation selectively through sympathoadrenal activation by angiotensin II. Three additional pressor dose-response curves for angiotensin II were obtained in each dog. The second dose-response curve was obtained after the administration of phentolamine and the third dose-response curve was obtained after the subsequent administration of sotalol. The final dose-response curve was obtained after partial recovery of the pressor responsiveness to norepinephrine and epinephrine from phentolamine blockade. The pressor responses for angiotensin II after phentolamine and sotalol (curve 3) were significantly smaller than those in the control dose-response curve (curve 1). No significant differences in the pressor responses to angiotensin II were noted after phentolamine when compared with those obtained after phentolamine plus sotalol (curve 2 vs. curve 3). The angiotensin II pressor responses after partial recovery from phentolamine (curve 4) did not differ significantly from those obtained in the control dose-response curve. These results of released catecholamines mediated through alpha adrenergic receptors in the pressor response to angiotensin II.