Central antihypertensive effects of inhibitors of the renin-angiotensin system in rats

The possibility that mean arterial pressure (MA) might be maintained by an effect of angiotensin II or its precursors on the central nervous system in rats made hypertensive by occluding the aorta between the renal arteries was investigated. Aortic coarctation produced severe hypertension (MAP greater than 150 mmHg) and plasma renin activity values (radioimmunoassay) at least 10 times normal within 2-6 days after surgery. [Sar1, IIe8]angiotensin II, an angiotensin II antagonist administered centrally via an intracerebroventricular (icv) injection (10-100 mug), lowered the MAP in a dose-dependent manner. Peripheral administration of [Sar1, IIe8]angiotensin II (bolus injection) at 100 mug intra-arterially was ineffective, but the antagonist did lower arterial pressure when infused intravenously for 1 h at 4 times this dose. Less than Glu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro, a converting enzyme inhibitor, and pepstatin, a renin inhibitor, were ineffective via an icv injection. These results suggest that angiotensin II is in part responsible for the elevation in blood pressure following aortic coarctation in rats. Both central and peripheral administration of [Sar1, Ile8]-angiotensin II lowered mean arterial pressure but the antagonist lowered arterial pressure at lower doses and produced a more rapid decline in arterial pressure when administered into the central nervous system then when administered intra-arterially or intravenously.