High-affinity aldosterone binding in rat liver--a re-evaluation.

The use of sodium molybdate as a stabilizing agent, and a RU26988 to exclude [3H]aldosterone from Type II glucocorticoid receptors, has enabled us to characterize high affinity Type I aldosterone binding sites in rat liver cytosol. In liver cytosols from male rats aldosterone bound with an affinity (Kd-22 degrees C) of 0.6 nmol/l (range 0.3-0.8 nmol/l), and Nmax 1.7 fm/mg protein (s.e.m. = 0.4); specificity of binding was similar to that for Type I sites in classical aldosterone target tissues (aldosterone greater than or equal to corticosterone greater than dexamethasone). Hepatic Type I receptor levels were relatively constant in both male and female rats aged 30-120 days, with levels significantly higher in females. Parallel studies on hepatoma H4 cells showed levels of Type I sites similar to those in normal liver, suggesting a general distribution of such sites throughout liver parenchyma, rather than a concentration in a specific cell type. The function of such Type I sites, and whether or not they are aldosterone-selective in vivo and can thus act as mineralocorticoid receptors, remains to be determined.