In vivo concentrations of kinins and angiotensins

In the investigation of hypotensive mechanisms for the converting enzyme (ACE) inhibitor, precise methods for plasma kinin and angiotensin II measurement are essential. We describe here determination methods of plasma kinin and angiotensin II, and their applications to converting enzyme inhibitor administration. In our kinin RIA system, a high titered antiserum (final dilution 1:640,000) was used. Sensitivity was 0.25 pg/tube. Regarding plasma kinin measurement, an inhibitor mixture including aprotinin, hexadimethrine, SBTI, phenanthroline and EDTA, was used to collect the plasma sample. The determined plasma kinin levels in normal subjects were below 10 pg/ml. A very sensitive and simplified direct RIA system for plasma angiotensin II was also developed in our laboratory using the very high titered antiserum (final dilution 1:1,500,000). The sensitivity was 0.1 pg/tube, and cross-reactivity of angiotensin I was less than 0.1%. These data suggest that plasma angiotensin II level can be determined directly in very small plasma samples, such as 0.1 ml by this RIA system even in the ACE inhibitor administration. The plasma angiotensin II levels in normal subjects were 12.0 pg/ml. Both of these RIAs which were applied to the clinical experiments of ACE inhibitor administration.