A simplified radioimmunoassay for plasma aldosterone employing an antibody of unique specificity

Abstract

A highly selective antibody for aldosterone, produced as indicated in the companion paper, was utilized as the basis for a radioimmunoassay for aldosterone in plasma which did not require fractionation of this compound from other steroids. No appreciable crossreactivity was found with any steroid tested except 18-hydroxy-11 deoxycorticosterone and 18-OH-corticosterone, but the affinity for these compounds was four orders of magnitude lower than for aldosterone. Specificity was further documented by demonstrating undetectable aldosterone levels in adrenalectomized dogs and supression of measured aldosterone levels to 0 in a dog subjected to Na loading and a course of deoxycorticosterone. Immunologic identity of standards and plasma aldosterone was demonstrated by showing that dilutions of a human plasma containing a high concentration of aldosterone paralleled a standard curve. Sensitivity, recovery, and accuracy of the method were tested and found satisfactory. Good correlation of results with a method employing chromatographic isolation of aldosterone was demonstrated. Aldosterone plasma values in normal human subjects in response to changes in posture and Na intake, as measured by this method, correlated in the expected fashion with changes in renin activity but did not correlate with plasma cortisol, which followed the anticipated diurnal cycle.