Stimulation of 11-β-hydroxysteroid dehydrogenase type 2 in rat colon but not in kidney by low dietary NaCl intake

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Abstract
Data suggest that mineralocorticoid selectivity is differentially regulated in epithelial target tissues. We investigated whether the level of dietary NaCl intake influenced the expression and tissue distribution of 11-β-hydroxysteroid dehydrogenase type 2 (11βHSD-2), aldosterone receptor (MR), and glucocorticoid receptor (GR) in rat colon, kidney, and cardiovascular tissue. Rats were fed a diet with 0.01 or 3% NaCl for 10 days. Messenger RNAs were analyzed with ribonuclease protection assay, 11βHSD-2 protein by Western blot analysis, and localization of GR and 11βHSD-2 by immunohistochemistry. NaCl restriction elevated plasma renin and aldosterone concentration, whereas corticosterone was unaltered. In distal colon, 11βHSD-2 mRNA and protein were augmented significantly by low-NaCl intake and immunolabeling was widely distributed in crypt and surface epithelium. The MR mRNA level was decreased, whereas GR mRNA was unaltered in distal colon. MR, GR, and 11βHSD-2 mRNAs were not changed in kidney cortex and medulla, left cardiac ventricle, and aorta. Immunofluorescence labeling showed that GR and 11βHSD-2 localization was mutually exclusive in kidney. In colon epithelium, nuclear staining for GR subsided as perinuclear 11βHSD-2 immunoreactivity increased with NaCl restriction. As a functional correlate of increased 11βHSD-2 expression in colon, the GR-stimulated sodium-hydrogen exchanger NHE-3 was lowered by NaCl restriction. Inhibition of 11βHSD-2 activity by carbenoxolone during NaCl restriction stimulated NHE-3 expression in colon. Dexamethasone stimulated NHE-3 both in colon and kidney. These data indicate that mineralocorticoid selectivity is physiologically regulated by NaCl intake at the level of 11βHSD-2 expression and tissue distribution in the distal colon, but not in the kidney.