A simple method measuring plasma aldosterone by radioimmunoassay without extraction

Abstract

A radioimmunoassay method was developed to measure plasma aldosterone levels.
Antibody was produced in rabbits by injecting aldosterone oxime coupled with bovine gamma-globulin once a month.
Plasma aldosterone was measured simultaneously by two methods : the direct method without extraction and a method using paper chromatography.
¹²⁵ I-aldosterone was used in the first method and ³H-aldosterone in the second.
The antibody had a high specificity adequate to show zero water blank in the first method.
Adequate precision, accuracy and sensitivity were obtained in a direct method using ¹²⁵I-aldosterone.
Plasma aldosterone levels were 7.1±3.0ng/100ml (Mean ±SD) in normal subjects and slightly higher after injecting ACTH-Z.
The correlative coefficient between the first and the second method was significantly high (r=0.970, P<0.001, n=37).
Plasma aldosterone was high (34.3±14.1ng/100ml, n=7) in primary aldosteronism, slightly high (14.2±2.6ng/100ml) in secondary aldosteronism, normal in Cushing's syndrome (10ng/100ml) and low in Addison's disease (1ng/100ml), hypopituitarism (1ng/100ml) and pseudoaldosteronism (2ng/100ml).
From these results, it is concluded that the direct method without extraction was a very useful and reliable method for measuring plasma aldosterone. It was superior in simplicity and there is no need to use a liquid scintillation counter.