The roles of plasma binding and receptor specificity in the mineralocorticoid action of aldosterone.

Abstract

The current hypothesis of the mechanism of action of aldosterone includes an initiating step of binding of the steroid to stereospecific receptor proteins in target tissues. In view of the very low circulating levels of aldosterone relative to other adrenal steroids, there must exist potent specificity—conferring mechanisms to insure appropriate aldosterone occupancy of mineralocorticoid receptors. Two specificity—conferring mechanisms are described which are posited to allow aldosterone occupancy of its appropriate receptor.In vitro, renal aldosterone binding sites are shown to fall into two classes. Those with a higher affinity for aldosterone—Kdlss (37 C)≅ 5X10-10—are termed Type I; those with a lower affinity—Kdiss (37 C)≅ 2.5 X lO-8— Type II. Desoxycorticosterone (DOC) has ∼80% the affinity of aldosterone for both sites. Corticosterone (B) has a high affinity for Type II sites, but less than 2% of the affinity of aldosterone for Type I. From the relative affinities of the three steroids for Type I, t...