The regulation of pressure by the renin angiotensin system

The availability of a potent angiotensin I converting enzyme inhibitor (CEI) has enabled the authors to assess the role of the renin angiotensin system in the regulation of arterial pressure in the unanesthetized dog. The nonapeptide CEI (SQ 20,881 Pyr Trp Pro Arg Pro Gln Ile Pro Pro) was administered to trained dogs with chronically implanted arterial and venous catheters. Intravenous administration of 5 mg of CEI was found to block the usual pressor response induced by intravenous injection of 1.0 μg of angiotensin I. The pressor response to angiotensin II was unchanged. In normal dogs on normal salt intake the injection of 5 mg of CEI did not alter arterial pressure or systemic plasma renin activity (PRA). However, in dogs on low salt diet, with slight systemic hypotension and significant elevation of PRA, blood pressure fell approximately 10 mm Hg when CEI was given; the PRA increased several fold. In adrenalectomized dogs adequately treated with cortisone acetate but maintained in a hypovolemic and hypotensive state on low dosage of DOCA and salt restriction, blood pressure fell 20-30 mm Hg within 3 minutes of injection of the CEI; PRA rose 5 fold or more. These observations demonstrate that the renin angiotensin system plays a quantitatively important role in the regulation of blood pressure in the hypovolemic and hypotensive state.