Digital Vascular Response to Angiotensin II in Normotensive and Hypertensive Subjects

Abstract

The critical opening pressure (COP) of digital vessels after digital nerve block and the change in COP caused by angiotensin at 4 mµg/kilo per min intravenously after the block were compared in 9 normotensive subjects, 8 patients with essential hypertension and 7 patients with various kinds of renal hypertension. The COP after nerve block was less than 20 mm Hg in the normotensives and in 6 renal hypertensives, but more than 20 mm Hg in 7 essential hypertensives. The angiotensin reduced the COP in 7 of the normotensives, increased it substantially in 7 essential hypertensives, but had little effect in 6 renal hypertensives. A significantly greater increase in systemic blood pressure occurred in the essential hypertensives than in the normotensive subjects. In normotensive subjects doses of intravenous angiotensin from 2 to 16 mµg/kilo per min decreased the COP whether preceded by digital nerve block or not. Angiotensin at 8 mµg/kilo per min increased total digital vascular resistance as estimated by venous occlusion plethysmography. The results indicated that angiotensin relaxed smooth muscle in digital vessels of normal subjects but increased vascular resistance. In patients with essential hypertension angiotensin caused contraction of the smooth muscle, a response apparently qualitatively different from normal. In renal hypertensives the smooth muscle had little response to the exogenous angiotensin.