Angiotensin II, Digital Blood Flow, and the Precapillary and Postcapillary Blood Vessels of Man

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Abstract
A number of polypeptides affect the smooth muscle of blood vessels. One such polypeptide is angiotensin. Although it is well known that angiotensin constricts the precapillary blood vessels its action on the venous system of man has not been adequately studied. The present study was undertaken to determine the effect of angiotensin II on the postcapillary blood vessels of the human digit of normotensive and hypertensive subjects as well as to compare the digital vascular responses to angiotensin with those to norepinephrine. These studies indicate that angiotensin II constricts primarily the precapillary blood vessels and has relatively little effect on the arteriovenous anastomoses and the postcapillary (capacitance) vessels. This is in marked contrast to norepinephrine which constricts all the digital blood vessels. Since angiotensin constricts the postcapillary blood vessels relatively little it appears to be a good drug for the treatment of cardiogenic shock associated with congestive heart failure and venous hypertension. Preliminary clinical experience with three patients with myocardial infarction and shock demonstrated that angiotensin II effectively elevated the arterial blood pressure without significantly altering the venous blood pressure. Furthermore studies on isolated venous segments in the forearm of man indicated the angiotensin II did not increase segmental venous pressure when injected directly into the isolated segment.

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