Improved Assay Methods for Renin "Concentration" and "Activity" in Human Plasma

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Abstract
Simplified methods are described for the measurement of human plasma renin "concentration" (PRC) and "activity" (PRA) based on the denaturation of renin substrate in which separation and concentration steps are avoided and recovery of renin is complete. In the PRA method effective inhibition of angiotensinase is achieved by warming plasma at pH 4.5 with EDTA followed by dialysis to pH 7.5. Neither renin nor renin substrate is affected by this treatment. In the PRC method, renin substrate is selectively denatured by warming at pH 3.3. After dialysis to pH 7.5 and addition of a standard substrate prepared from nephrectomized sheep, incubation results in a linear increase of pressor material which is assayed without extraction on rat blood pressure against synthetic angiotensin. Specificity is established by nephrectomy and immunological studies. The linear relationship between plasma renin concentration and reaction rate contrasted with the nonlinearity observed with renal renin. The systems are suitable for routine diagnostic use.