Background. Although the renal cortical collecting duct (CCD) is a principal target for aldosterone, recent evidence suggests that salt transport by other nephron segments may also be regulated by aldosterone. Electroneutral and thiazide-sensitive NaCl cottansport by the distal convoluted tubule (DCT) of the rat is increased in animals deprived of dietary NaCl. We tested the hypothesis that the DCT of the rabbit is an aldosterone target tissue. Methods. The single-nephron reverse- transcriptase/polymerase chain reaction (RT-PCR) technique was used to determine mRNA expression of NaCl cotransporter and 11β-HSD 2 in dissected nephron segments. The rabbit NaCl cotransporter was first cloned and rabbit- specific primers selected. A micro-assay was developed to assess 11β-HSD 2 enzyme activity in0.5 mm samples of the same nephron segments. Results. NaCl cotransporter was expressed in 0 of 6 proximal tubule (PT), 6 of 6 DCT and 3 of 6 CCD samples, while 11β-HSD was found in 0 of 7 PT, 7 of 7 DCT and 9 of 9 CCD samples. Corticosterone was converted to 11-dehydrocorticosterone at a high rate and to a similar extent by both the DCT and CCD, but not the PT. Conclusions. We conclude that the DCT is a target tissue for the action of aldosterone. Axial heterogeneity of electroneutral (in DCT) and electrogenic (in CCD) Na transporters along the distal nephron may improve sodium recovery in low salt and volume states.
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