No abstract

By inactivating potent glucocorticoid hormones (cortisol and corticosterone), 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2) plays an important role in the placenta by controlling fetal exposure to maternal glucocorticoids, and in aldosterone target tissues by controlling ligand access to co-localized glucocorticoid and mineralocorticoid receptors. Amino acid sequence from homogeneous human placental 11 beta-HSD2 was used to isolate a 1897 bp cDNA encoding this enzyme (predicted M(r) 44126; predicted pI 9.9). Transfection into mammalian (CHO) cells produces 11 beta-HSD2 activity which is NAD(+)-dependent, is without reductase activity, avidly metabolizes glucocorticoids (Km values for corticosterone, cortisol and dexamethasone of 12.4 +/- 1.5, 43.9 +/- 8.5 and 119 +/- 15 nM respectively) and is inhibited by glycyrrhetinic acid and carbenoxolone (IC50 values 10-20 nM). Rabbit antisera recognizing 11 beta-HSD2 have been raised to an 11 beta-HSD2-(370--383)-peptide-carrier conjugate. Recombinant 11 beta-HSD2, like native human placental 11 beta-HSD2, is detectable with affinity labelling and anti-11 beta-HSD2 antisera, and appears to require little post-translational processing for activity. 11 beta-HSD2 mRNA (approximately 1.9 kb transcript) is expressed in placenta, aldosterone target tissues (kidney, parotid, colon and skin) and pancreas. In situ hybridization and immunohistochemistry localize abundant 11 beta-HSD2 expression to the distal nephron in human adult kidney and to the trophoblast in the placenta. 11 beta-HSD2 transcripts are expressed in fetal kidney (but not lung, liver or brain) at 21-26 weeks, suggesting that an 11 beta-HSD2 distribution resembling that in the adult is established by this stage in human development.

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) converts the active glucocorticoid corticosterone to inactive 11-dehydrocorticosterone in the rat (or cortisol to cortisone in man), thereby protecting renal mineralocorticoid receptors from corticosterone or cortisol and allowing preferential access for aldosterone. We have previously demonstrated that cortisol-induced cutaneous vasoconstriction in man is potentiated by the 11 beta-OHSD inhibitor glycyrrhetinic acid, suggesting that 11 beta-OHSD may protect vascular corticosteroid receptors. In this study we report quantitation of 11 beta-OHSD bioactivity in homogenates of rat aorta, mesenteric artery, caudal artery, and heart, expressed as the percent in vitro conversion of 3H-corticosterone to 3H-11-dehydrocorticosterone. Nicotinamide adenine dinucleotide phosphate (NADP+)-dependent 11 beta-OHSD activity was found in all of these tissues and was significantly higher in resistance vessels than aorta (P less than 0.05) [without NADP+: caudal artery (4.2 +/- 0.2%) greater than mesenteric artery (2.5 +/- 0.7%) = heart (1.67 +/- 0.2%) greater than aorta (0.79 +/- 0.2%); with 200 microM NADP+: caudal artery (43.9 +/- 2.1%) greater than heart (20.6 +/- 1.0%) = mesenteric artery (17.7 +/- 3.1%) = aorta (11.4 +/- 0.4%); heart greater than aorta]. All of these were lower than renal cortex (29.4 +/- 1.8% without NADP+; 82.4 +/- 0.4% with NADP+; P less than 0.001). 3H-11-dehydrocorticosterone was the major metabolite of 3H-corticosterone (greater than 97% of 3H-corticosterone metabolized). Reduction of 3H-11-dehydrocorticosterone to 3H-corticosterone was not detected in these experiments. We also report localization of 11 beta-OHSD-like immunoreactivity by immunohistochemistry using antisera raised against rat liver 11 beta-OHSD, and of 11 beta-OHSD messenger RNA expression by in situ hybridization using complementary RNA probes transcribed from complementary DNA encoding rat liver 11 beta-OHSD. We found 11 beta-OHSD immunoreactivity and messenger RNA expression in vascular and cardiac smooth muscle cytoplasm but not in endothelium. Thus, 11 beta-OHSD is appropriately sited to modulate access of corticosterone to vascular receptors and could influence vascular resistance, cardiac output and thereby blood pressure.