Role of the autonomic nervous system in the inotropic variations induced by the infusion of angiotensin II

Abstract

Inotropic effects of angiotensin II were studied in 26 anesthetized dogs with different conditions of autonomic activity. The values of maximal velocity of contraction (V(max)TP) were compared before and 10 min after the arterial pressure was elevated by the infusion of the drug. In eight dogs, previously treated with atropine and reserpine, the administration of angiotensin had no effect on mean values of V(max)TP. Nine animals submitted to ganglionic blockade by hexamethonium presented an improvement of myocardial contractility when angiotensin was infused. In nine dogs studied with intact nervous system, infusion of the drug was accompanied by decrease of mean values of the index. It was concluded that the polypeptide exerts no important physiological effects upon myocardial contractility without the mediation of the autonomic nervous sytem. It was considered that the positive inotropic effect verified in dogs under ganglionic blockade was due to adrenergic hyperactivity induced by angiotensin. The depression of the contractile state observed in intact animals was supposed to be mediated by variations of autonomic nervous sytem activity consequent to baroreceptor reflex.