The Effects of the Antagonists of the Renin—Angiotensin System on Cardiovascular Response to Lower-Body Subatmospheric Pressure in the Anaesthetized Cat

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Abstract
1. Lower-body subatmospheric (negative) pressure led to a prompt reduction in central venous pressure and arterial blood pressure. Arterial blood pressure was then restored within 30 s and there was a tachycardia. These reflex responses have been used to investigate the role angiotensin plays in blood pressure control. 2. The initial plasma renin activity (2.9 ng of angiotensin I h−1 ml−1) did not change during the brief lowering of pressure. Before pressure was lowered neither the angiotensin-converting enzyme inhibitor nor a competitive antagonist, [Sar1,Ala8]-angiotensin II, lowered arterial pressure. 3. Nevertheless, after inhibition of the renin-angiotensin system by these agents, the reduction in blood pressure induced by lower-body negative pressure became greater and the blood pressure recovery was impaired. 4. The findings suggest that angiotensin, at a blood concentration which has no direct effect on blood pressure, interacts with the sympathetic nervous system to maintain arterial blood pressure.