A Radioimmunoassay for Aldosterone in Human Peripheral Plasma Including a Comparison of Alternate Techniques

Abstract

An accurate and relatively simple radioimmunoassay method for the measurement of aldosterone in human plasma is described. One ml or less plasma with ³H aldosterone (2 pg) is extracted with dichloromethane. Two alternative purification steps are described, either a standard paper chromatography (B₅) or a more rapid Sephadex LH-20 column (60 × 1 cm) in the system dichloromethane: methanol 98:2 provides adequate purification for analysis. The assay uses either an antibody of high specificity generated against aldosterone-18, 21-disuccinate, or the 3-oxime coupled to bovine albumin. The samples, or standards, are incubated for 1–2 hours at 5° C with dilute antibody and ³H aldostercne. Separation of bound from free aldosterone is affected with activated and coarse-graded Florisil. This one-day method, using the disuccinate antibody and the LH-20 column, is associated with blank values difficult to distinguish from zero (< 6 pg). Aldosterone values from adrenalectomized subjects or duplicate samples after cortisone addition (2 μg/100 ml) give undetectable values. Accuracy studies yield essentially a zero intercept and a slope similar to 1.0. When various plasma samples were measured by either an established double isotope derivative method or by the radioimmunoassay using either the paper or LH-20 column purification steps, the values obtained by analysis of variance were not significantly different.