Aldosterone binding along the rabbit nephron: an autoradiographic study on isolated tubules

The sites of action of aldosterone (A) along the tubule of rabbit kidney were studied by autoradiographic localization of mineralocorticoid-binding sites on microdissected tubular segments. Kidney pyramids were incubated at 30 degrees C for 1 h in a collagenase solution with [3H]aldosterone at a concentration of 1.5 X 10(-9) M with and without an excess unlabeled A. Tubular segments were then microdissected and transferred onto dry film; fixation and staining were done only after exposure of the film 4 mo later in order to avoid diffusion. Specific nuclear labeling was 19.0 +/- 1.3 silver grains/100 micrometers2 in distal convoluted tubules (n = 28) and 21.0 +/- 1.8 in cortical collecting ducts (n = 18). No difference between these two structures was observed (P greater than 0.1, paired t test, n = 15). No specific binding was found in the proximal tubule (0.5 +/- 0.4, n = 17). In the thick ascending limb of Henle's loop, the labeling was low (3.9 +/- 0.9, n = 16). We conclude that, in the rabbit kidney, nuclear mineralocorticoid-binding sites, presumably receptors, are present in the distal and cortical collecting tubule.