Measurement of Renin in Human Plasma

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Abstract
In order to obtain a simple measurement of the concentration of renin in human plasma, kinetic studies have been performed for the following enzymatic reactions: hog renin reacting with cat angiotensinogen, human renin reacting with cat angiotensinogen, and human renin reacting with human angiotensinogen. The reaction kinetics of the competition between human and cat angiotensinogen for human renin have also been investigated. From the result of these studies a micro-method was devised characterized by a precisely defined concentration of the angiotensinogen during the reaction, controlled activity of the angiotensinases, and gentle preparative treatments. The principle consists of mixing cat plasma angiotensinogen with the human plasma to be tested, and then determining the velocity of the reduction of the concentration of cat angiotensinogen during the reaction. The concentration of angiotensinogen is measured by transforming it to angiotensin under conditions where the angiotensin is stable. After an additional determination of the initial concentration of human angiotensinogen, the initial velocity, which is proportional to the concentration of renin, can be calculated. In some plasma samples the renin activity was measured both by the method of Boucher and by the method introduced here. The correlation between the results obtained by the two methods is very high. The coefficient of correlation is +0.92.