Role of 11β-Hydroxysteroid Dehydrogenase in Nongenomic Aldosterone Effects in Human Arteries

—The aim of the present study was to demonstrate rapid effects of aldosterone on the Na+ -H+ exchanger in strips of human vascular vessels and to determine whether 11β-hydroxysteroid dehydrogenase enzyme (11β-HSD) could play a protective role in this response, such as that described for the classic type I mineralocorticoid receptor (MR). The activity of 11β-HSD isoforms 1 and 2 were measured in fetal and adult arteries. Both isoforms are present in adult and fetal vessels. However, a significant difference in the proportion of each isoform was found. Isoform 1 activity (in pmol · min−1 · 100 mg−1 protein) was 42±5 in fetal vessels and 29±2 in adult arteries, and isoform 2 activity was 78±7 in fetal and 12±2 in adult tissue. The nongenomic effect of aldosterone on Na+ -H+ exchanger activity was measured in strips of chorionic and radial uterine arteries loaded with the pH-sensitive dye 2′,7′-bis(2-carboxyethyl)-5,6-carboxyfluorescein. Recordings of intracellular pH (pHi ) were made by videofluorescence microscopy. Aldosterone (0.5 nmol/L) rapidly increased pHi , with a half-maximal effect between 2 and 3 nmol/L in both fetal and adult vessels. Ethylisopropylamiloride, a specific inhibitor of the Na+ -H+ exchanger, inhibited this effect. The hormone-mediated increase in pHi was unaffected by spironolactone, a classic antagonist of MR, but was completely blocked by RU28318. Cortisol (up to 1 μmol/L) had no effect on pHi , but when applied in the presence of carbenoxolone, a dramatic increase in Na+ -H+ exchanger activity was evident. The increments on pHi for each cortisol concentration were similar to those observed for aldosterone. These findings suggest that vascular 11β-HSD plays an active role in maintaining the specificity of the rapid effects of aldosterone.