11 beta-hydroxysteroid dehydrogenase isoforms and their implications for blood pressure regulation

11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) catalyzes the reversible conversion of physiological glucocorticoids (cortisol, corticosterone) to inactive products. The enzyme thus protects non-selective renal mineralocorticoid receptors from circulating glucocorticoids (ensuring aldosterone-selectivity in vivo), excludes maternal glucocorticoids from the foetal circulation and modulates glucocorticoid access to glucocorticoid receptors in other tissues. 11 beta-HSD has been purified from rat liver, antisera raised, a cDNA isolated and its human homologue cloned. However, it is difficult to reconcile all of the actions of 11 beta-HSD with a single enzyme. Here data are reviewed that demonstrate not only molecular heterogeneity of the 'liver-type' 11 beta-HSD, but also the existence of a novel high affinity isoform in the placenta and perhaps distal nephron. These data are discussed in the light of their potential physiological and pathological importance, with particular reference to the pathogenesis of hypertension.