Angiotensin II control of regional haemodynamics in rats with aortocaval fistula.

Regional perfusion is reduced and the renin-angiotensin system is activated in rats with aortocaval fistula. The effects of captopril (angiotensin converting enzyme inhibitor), losartan (AT1 receptor antagonist), and PD 123319 (AT2 receptor antagonist) on regional blood flow and vascular conductance were assessed in rats with aortocaval fistula and sham-operated rats. Control of blood flow and vascular conductance by angiotensin II was evaluated by serial bolus injections of captopril, losartan, and PD 123319 in anaesthetized rats. In rats with fistula, PD 123319 significantly decreased, while captopril and losartan increased, mesenteric blood flow. The decrease in mesenteric blood flow by PD 123319 was significantly greater in rats with fistula compared to sham. Captopril and PD 123319 significantly decreased renal blood flow compared to losartan which increased it. In sham rats, captopril and losartan significantly increased, while PD 123319 decreased, mesenteric and renal conductance. In rats with fistula, captopril and losartan significantly increased, while PD 123319 decreased, mesenteric conductance. The significant increase produced by losartan on mesenteric conductance was greater in rats with fistula compared to sham. PD 123319 produced a significantly greater decrease in renal conductance of aortocaval fistula compared to sham rats. Captopril, losartan and PD 123319 did not significantly affect perfusion in hindquarter in rats with fistula or sham. The renin-angiotensin system is more active in the control of regional haemodynamics in rats with aortocaval fistula, and acts as mechanism of maintaining normal arterial blood pressure in these animals. In rats with fistula, AT1 receptors predominate in regulating regional haemodynamics. This article is protected by copyright. All rights reserved.