Myocardial Actions of Angiotensin

• The cardiovascular effects of angiotensin have been studied extensively since its identification 25 years ago." The synthesis of various angiotensins and the demonstration of the pharmacological identity of the naturally occurring and the synthetic octapeptides have facilitated such studies in recent years. It has been found consistently that angiotensin is a powerful constrictor of arteriolar smooth muscle, increases total peripheral resistance, and raises the systemic arterial pressure. No such agreement exists concerning the actions of the drug on heart muscle. Of 32 published studies on changes in the normal human or animal circulation following administration of angiotensin, 19 have found that cardiac output is decreased and 13 that it remains unchanged. Increases of diastolic volume of the heart, of left ventricular end diastolic pressure, of diastolic pressures in the other cardiac chambers, of pulmonary wedge pressure, of central venous pressure, and of circulation time have also been observed following introduction of angiotensin into the intact circulation.^ These observations have led some workers to conclude that angiotensin depresses the strength of contraction of heart muscle or that it lacks inotropic action on the heart.'-On the other hand, studies in which myocardial contractility was evaluated more directly suggest that at least some concentrations of angiotensin exert positive inotropic effects on mammalian myocardium. St ~Some of these reports describe only a few observations or yield no quantitative data; the increases in contractility observed in the other studies