A human gamma globulin, that was treated with pepsin and is readily soluble in water, has been found to be superior to the usually employed human gamma globulin as a carrier protein in order to attain a satisfactory separation of the antibody-bound steroid from the free. The separation procedure using the water soluble gamma globulin was successfully applied to develop a reliable and stable radioimmunoassay of plasma aldosterone.
Using this method, the mean plasma aldosterone level in 17 normal subjects taken at 8 : 00 a.m. was 12. 3±4. 4ng/100ml (mean±SD, range 4. 0, -18.5) with a normal diet (Na 220-340mEq, K 75mEq/day) in the hospital. This normal level was similar to that reported by other investigators using radioimmunoassay. High plasma aldosterone levels were found in patients with primary aldosteronism (50. 9±19. 7, range 28.7-89.0, n=6) and renovascular hypertension (17. 0, 32. 2, 44. 0). The mean plasma aldosterone level in patients with low renin essential hypertension was 6. 2±4. 0 (range 1.6-15.6, n=17), which was significantly (P<0. 01) lower than that found in patients with normal renin essential hypertension (10. 7±4. 8, range 3. 6-20. 5, n=22) or that of normal subjects.