HIGH-AFFINITY NAD(-DEPENDENT 11-BETA-HYDROXYSTEROID DEHYDROGENASE IN THE HUMAN HEART())

Receptor-ligand binding is an essential component of mineralocorticoid (MC) activity in target tissues. Detection of type 1 mineralocorticoi d receptors (MR) in cardiac tissue is therefore suggestive that, like kidney, the heart is MC responsive. The presence of 11 beta-hydroxyste roid dehydrogenase (11 beta-HSD) within MC responsive tissue is essent ial to prevent saturation of MR by glucocorticoids. Using both high-pe rformance liquid chromatography (HPLC) and thin layer chromatography ( TLC), we have found that a high-affinity species of 11 beta-HSD predom inates within human heart. Although two 11 beta-HSD isoforms were dete cted in human cardiac tissues, the activity of high-affinity (type 2) 11 beta-HSD was found to be at least twice that of low affinity (type 1) 11 beta-HSD. Human cardiac type 2 11 beta-HSD possesses characteris tics identical to the high-affinity enzyme of distal renal tubules; 11 beta-dehydrogenation of corticosterone or cortisol to their 11-keto m etabolites is NAD(+)-dependent and, with corticosterone as substrate, the enzyme has a nanomolar K-m (15.1 nM as determined by Lineweaver-Bu rke analysis). Furthermore, its activity is unidirectional; corticoste rone and cortisol are 11 beta-dehydrogenated to inactive 11-keto metab olites, whereas 11-oxoreductase activity (conversion of 11-dehydrocort icosterone and cortisone to corticosterone and cortisol, respectively) is absent, RT/PCR analysis, using primers complementary to the human renal type 2 11 beta-HSD sequence, demonstrated that the high-affinity species of 11 beta-HSD expressed in human heart is indeed the same en zyme as that produced in the kidney. These findings strongly suggest t hat, as is the-case in the distal portion of the nephron, type 2 11 be ta-HSD plays an important role in the human heart to promote glucocort icoid metabolism and to confer MC specificity upon MR. (C) 1996 Academ ic Press Limited