[A simple method for measuring aldosterone secretion rate using 125I-aldosterone (authors' transl)]

A simplified radioimmunoassay system for aldosterone secretion rate was developed by using radioiodine-labelled aldosterone and highly specific antiserum to aldosterone. An antibody was produced in rabbits by injecting aldosterone-oxime coupled with bovine gamma-globulin once a month. Aldosterone-oxime was labelled with 125I by using the chloramine T method described by Hunter and Greenwood. 3 ml of a twenty-four-hour urine specimen was used for the radioimmunoassay. Following CH2Cl2 extraction, pH 1 hydrolysis was carried out for twenty-four hours. Separation of the aldosterone extract was achieved by paper chromatography (hexane:benzene:methanol:water = 1:9:5:2.5). The minimum measurable concentration was under 1pg, and adequate intraassay and interassay precision were obtained. Aldosterone secretion rate was 89.6 +/- 25.8 (mean +/- SD)mug/day in normal subjects and was similar in low- and normal-renin essential hypertension. Significant high values (806.4 +/- 65.8mug/day) were obtained in primary aldosteronism and were slightly high in secondary aldosteronism and high-renin essential hypertension. The aldosterone secretion rate correlated positively with plasma aldosterone level (r = 0.731, p < 0.01). Aldosterone secretion rates were obviously higher than plasma levels in primary and idiopathic aldosteronism. From these results, it is concluded that this method is a very useful and reliable one for measuring aldosterone secretion rate and for discriminating primary aldosteronism from low-renin essential hypertension. it is superior in its simplicity, and there is no need to use a liquid scintillation counter.