Regulation Of 11β-Hydroxysteroid Dehydrogenase Enzymes By Dietary Sodium In The Rat

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Abstract
11β-Hydroxysterold dehydrogenase enzymes (11β-HSD1, 11β-HSD2) regulate access of adrenocorticosteroids to receptors. 11β-HSD2 is a dehydrogenase that protects mineralocorticoid receptors from circulating glucocorticoid hormones, 11β-HSD1 is a reductase that promotes formation of active hormone in glucocorticoid-sensitive tissues. Here we investigate whether low or high sodium diets affect 11β-HSD enzyme activities and mRNA expression in liver and kidney tissues. 11β-HSD activity was measured as dehydrogenation of 3H-corticosterone by microsomes in the presence of NAD or NADP. In situ hybridisation techniques were used to assess expression of 11β-HSD1 mRNA (liver and kidney) and 11β-HSD2 mRNA (kidney). Dietary sodium did not affect 11β-HSD2 mRNA expression in collecting tubules of the medulla: 11β-HSD1 mRNA in proximal tubules of the inner cortex/outer medulla was lower after a high sodium diet. 11β-HSD1 mRNA in liver was unaffected by treatment. Renal enzyme activity with NAD (11β-HSD2 cofactor) was lower following a high sodium diet (P < 0.05). In the presence of NADP (11β-HSD1 co-factor), neither renal nor hepatic activities were affected. Dietary sodium restriction appears to increase 11β-HSD activity by a non-genomic mechanism; this should enhance aldosterone specificity for mineralocorticoid receptors. 11β-HSD1 mRNA expression varies independent of enzyme activity and is not clearly related to altered glucocorticoid activity.
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