Effect of the angiotensin II blocker 1-Sar-8-Ala-angiotensin II on renal artery clip hypertension in the rat.

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Abstract
Twenty-four conscious male Wistar rats with hypertension induced by left renal artery clipping (two-kidney hypertension) were infused intravenously with 1-Sar-8-Ala-angiotensin II a competitive angiotensin II antagonist. The spectrum of responses was wide, ranging from a mild elevation in blood pressure to a marked fall in blood pressure, despite effective and specific angiotensin blockade in all cases. The change in blood pressure during 1-Sar-8-Ala-AII infusion activity showed a significant correlation with the level of plasma renin prevailing immediately before the infusion (r = - 0.78, P less than 0.01) but not with the prevailing blood urea level (r = 0.27, 0.1 greater than P greater than 0.05), the drgree of hypertension (r = 0.42, 0.1 greater than P greater than 0.05), or the time since clipping (r = 0.02, P greater than 0.05). There was no significant correlation between the degree of hypertension and the plasma renin activity (r = 0.42, 0.1 greater than P greater than 0.05). In rats with blood pressure drops greater than 20 mm Hg in response to 1-Sar-8-Ala-AII, the final blood pressure level was still above the normotensive range. Excision of the clipped kidney reduced blood pressure to normal or to near normal within 24 hours in all of the rats tested. It is concluded that the degree of dependence of renal hypertension on the renin-angiotensin system is directly related to the increase in circulating angiotensin itself and not to an increase in sensitivity to angiotensin. Other factors appear to be involved in renal clip hypertension in addition to circulating renin and angiotensin, especially when the measured activity of plasma renin is normal.