Effects of angiotensin I converting enzyme inhibitor (SQ 14225) on control of aldosterone

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Abstract
To study effects of angiotensin I converting enzyme inhibitor (CEI), SQ 14225, on plasma aldosterone (PA), angiotensin I (AI), angiotensin II (AII), potassium and ACTH were administered with or without the simultaneous injection of SQ 14225 in rabbits. The direct effect of bradykinin on PA was also examined, since it is suspected to augment the action of kinin under the administration of CEI. In rabbits the dose of 1 mg/kg of SQ 14225 by a bolus injection resulted in a marked elevation of plasma renin activity (PRA) and moderate but significant decreases in circulating AII and PA with only a little change of blood pressure. Decrements in circulating AII and those in PA observed after the injection of SQ 14225 were well correlated (r = 0.585, P < 0.05). Stimulatory effects of AII, potassium and ACTH on PA were not affected by SQ 14225, however, those of AI on PA and blood pressure were completely inhibited by pre-treatment of SQ 14225. The infusion of bradykinin showed a remarkable reduction in blood pressure and a small increment in PRA, circulating AII and PA. These results may suggest that the inhibitory effect of acutely administered SQ 14225 on PA is mainly due to the inhibition of conversion from AI to AII, but not direct effects on adrenal glands. Furthermore, it was suggested that the augmented kinin is not related to the inhibitory effect of SQ 14225 on PA. In addition, the administration of SQ 14225 does not change the effects of potassium and ACTH on PA.