Binding and action of aldosterone, dexamethasone, 1-25(OH)2D3, and estradiol along the nephron

The localization of specific binding sites of four steroids--aldosterone, dexamethasone, 1-25-dihydroxycholecalciferol and estradiol--is described along the nephron. This localization has been determined by using an autoradiographic method on dry films, applied to intact microdissected tubular segments. Aldosterone binds specifically to nuclei of the distal and cortical collecting tubule. No specific labeling was observed in the cytoplasm. This localization corresponds to the known sites of action of aldosterone on sodium reabsorption. Specific nuclear binding of dexamethasone is present all along the tubule except the proximal tubule. In this latter part of the nephron, a specific cytoplasmic labeling is observed, in the absence of nuclear labeling. This cytoplasmic binding could correspond to physiological effects in this structure, via non-genomic mechanisms. 1-25(OH)2D3 nuclear binding is located mainly in the loop of Henle and medullary collecting tubule, which are the sites of synthesis of calcium-binding proteins. No specific binding of estradiol is present in any part of the nephron.