Aldosterone binding in isolated tubules. IV. Autoradiography along the nephron of the spontaneously hypertensive rat.

The binding of aldosterone was studied in tubular segments isolated by microdissection from kidneys of spontaneously hypertensive (SHR, n = 8), Kyoto normotensive (KWR, n = 8), and normal Wistar (NWR, n = 6) rats with an autoradiographic technique on dry film. All animals had been previously adrenalectomized. Kidney pyramids were incubated in vitro before microdissection with collagenase and 2 X 10(-9) M [3H]aldosterone in the presence or absence of an excess of unlabeled aldosterone. In addition, the displacement of the binding by 10 times excess dexamethasone or aldosterone was examined in the cortical and medullary collecting tubule of SHR and KWR to assess the specificity of binding sites. In the three groups, no specific nuclear labeling was detectable in the proximal tubule. The highest specific nuclear labeling was found in the distal portions of the nephron, and intermediate values were present along the loop of Henle. In the cortical collecting tubule, the most specific mineralocorticoid segment, the specific nuclear binding, expressed in silver grains per unit surface, was significantly elevated in SHR (16.1 +/- 1.5) and KWR (13.7 +/- 1.5) as compared with NWR (10.2 +/- 0.8, P less than 0.001 and less than 0.05, respectively). The difference between SHR and KWR did not reach statistical significance. In the medullary collecting tubule, binding was higher in SHR (14.3 +/- 1.6) than in both KWR (8.7 +/- 1.0, P less than 0.005) and NWR (10.1 +/- 0.9, P less than 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)