Radioimmunoassay of Angiotensin I: Comparison of Two Renin Activity Methods and Use for Other Measurements of the Renin System

Abstract

Abstract Standard curves for radioimmunoassay of angiotensin I vary with the amount of plasma or plasma extract present in the assay samples. Therefore results of all such analyses must be compared with standards processed precisely like the unknowns. Results of renin activity, assayed directly in plasma or plasma extracts, corresponded well, demonstrating the comparability of the two types of methods. We describe simplifications in measuring activity, substrate, and concentration of renin, and emphasize use of the optimum pH for determining action of the enzyme. In addition, we present evidence for the presence of angiotensin I in the circulation, especially after renin secretion is stimulated.