[Binding of steroid hormones in the kidney]

The localization of mineralocorticoid and glucocorticoid binding sites along the nephron has been investigated by using an autoradiographic technique (dry film) and biochemical methods, applied on tubular segments of rabbit and rat kidney, isolated by microdissection, after in vitro incubation of kidney pyramids with tritiated aldosterone (Aldo) or dexamethasone (Dex). Based on analysis of dose-dependent specific nuclear binding values and competition studies, cortical collecting tubule (CCT) appears as the most specific mineralocorticoid segment; the distal tubule exhibits also high binding values, which are less specific for Aldo than in CCT; Aldo binding was lower in the ascending limb of Henle's loop and medullary collecting tubule and of mixed (gluco and mineralocorticoid) specificity. Aldo receptors were not present in proximal tubule and glomerulus. Specific nuclear binding of Dex was high all along the nephron, except in proximal tubules, and somewhat lower in glomeruli and its arterioles than in the distal parts of the nephron. Binding of 3H-Aldo did not differ drastically along the nephron of the rat and the rabbit.