Role of the pressor action of angiotensin II in experimental hypertension.

Experiments with rabbit aortic strips and pithed rats indicated that l-Sar-8AJa-angiotensin II (Sar-Arg-Val-Tyr-Val-His-Pro-Ala) is a specific competitive antagonist of the vascular action of angiotensin II. Norepinephrine-induced hypertension was not affected by infusions of l-Sar-8-Ala-angiotensin II which evoked a dose-related reduction of angiotensin II-induced hypertension in conscious rats. Infusions of l-Sar-8-Ala-angiotensin II that caused a doserelated reduction of the blood pressure of conscious rats in the acute phase of unilateral renal hypertension were ineffective during the chronic phase of such hypertension. Infusions of l-Sar-8-Ala-angiotensin II lasting 1 hour did not reduce the blood pressure of normotensive, spontaneously hypertensive, or metacorticoid hypertensive conscious rats. These data indicate that, under certain experimental conditions, the blood pressure of rats during the acute phase of unilateral renal hypertension is maintained by the endogenous angiotensin II previously demonstrated to be present in the plasma in supernormal concentrations. The blood pressure of normotensive, spontaneously hypertensive, metacorticoid hypertensive, and chronic unilateral renal hypertensive rats previously shown to have normal plasma levels of renin and angiotensin II appeared to be independent of the pressor action of endogenous angiotensin II. This is additional direct evidence implicating the pressor action of angiotensin II in the etiology of renal hypertension.