BackgroundAn isoenzyme of 11β-hydroxysteroid dehydrogenase (11β-HSD), 11β-HSD-2 confers aldosterone specificity on the mineralocorticoid receptor (MR) and is found collocated in renal cortical collecting duct cells with the MR. To investigate whether the salt sensitivity of the Dahl salt-sensitive (S) rat is due to 11β-HSD deficiency, we measured 11β-HSD-1 and 11β-HSD-2 mRNA levels in the kidneys of Dahl-S and Dahl salt-resistant (R) rats. In addition, we studied the effects of gender, age and dietary sodium on expression of mRNA for the two isoforms. S and R rats were placed on low- or high-sodium (HNa) diets and sacrificed after 33 and 115 days. Rat kidney RNA was isolated and 11β-HSD-1 and 11β-HSD-2 mRNA levels were measured on Northern filter hybridization using isoform-specific probes.ResultsNo strain differences were observed in the mRNA expression of the two isoforms of 11β-HSD under any of the experimental conditions. No gender or age differences were observed in 11β-HSD-2 mRNA but HNa diet almost doubled 11β-HSD-2 mRNA (P< 0.0009). 11β-HSD-1 mRNA levels were consistently higher, more than double, in male rats versus females rats (P< 0.0001), and in the 115-day-old rats versus the 33-day-old rats (P< 0.0001). Dietary sodium intake did not affect 11β-HSD-1 mRNA levels.ConclusionsThere is no difference in the expression of the two isoforms of 11β-HSD in the kidneys of the S and R rats, which might explain the salt sensitivity and higher blood pressure of the S rat. Renal 11β-HSD-1 mRNA levels are higher in male than in female rats, and in the older rats of both strains. In the kidney, the 11β-HSD-2 gene is regulated by sodium status but is not affected by gender or age.