Myocardial Actions of Angiotensin

Synthetic angiotensin a has pronounced inotropic effects on isometrically contracting, isolated papillary muscles of kittens. The response increases with drug concentration over the range from 10-10 M to 10-5 M. The mean maximum increase in tension development is 120%. Contractility is raised by angiotensin through an increase in the degree of activation of the contractile elements with no significant change in the duration of their active state. Low concentrations of angiotensin have a greater inotropic action than equimolar concentrations of l-norepinephrine; but the maximum inotropic effect obtainable with l-norepinephrine is almost twice that of angiotensin. The inotropic effects of angiotensin on cat atrial muscle are slight, and the drug is inactive on frog ventricular myocardium. It has no effect on the resting length-tension relationship of mammalian atrial or ventricular muscle. The frequency of impulse formation in the SA node is not significantly changed by concentrations of angiotensin up to 1...