Carbenoxolone Damages Endothelium and Enhances Vasoconstrictor Action in Aortic Rings

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Abstract
Abstract Carbenoxolone causes hypertension indirectly by inhibition of 11β-hydroxysteroid dehydrogenase and consequent elevation of intracellular glucocorticoid levels and enhancement of vasoconstrictor action. We performed the present study to determine whether carbenoxolone also enhances vascular tone directly by mechanisms independent of glucocorticoids and other systemic influences. Exposure of rat aortic rings to 10 to 100 μmol/L carbenoxolone in aerated Krebs-Henseleit buffer for 24 hours resulted in concentration-dependent increases in angiotensin II (Ang II) (100 nmol/L)–stimulated contractions and significant shifting of the phenylephrine cumulative contraction curve to the left but not increases in KCl (120 mmol/L)–stimulated contractions. Maximal enhancement of Ang II contraction was 39%. In contrast, brief (15-minute) exposure to 100 μmol/L carbenoxolone did not alter Ang II contractions. Mechanical denudation of the endothelium obviated enhancement of Ang II contractions by carbenoxolone, suggesting interaction of carbenoxolone with the endothelium. Endothelium-dependent relaxation of precontracted rings to acetylcholine or ATP was reduced by more than 90% by 24-hour pretreatment with 100 μmol/L carbenoxolone but not with 100 μmol/L deoxycorticosterone acetate (a mineralocorticoid) or 100 μmol/L glycyrrhizic acid (a natural 11β-hydroxysteroid dehydrogenase inhibitor). Vascular smooth muscle relaxation with sodium nitroprusside was not inhibited by carbenoxolone. Incubation of cultured endothelial cells with 100 μmol/L carbenoxolone for 24 hours did not inhibit nitric oxide synthase activity, as measured by conversion of [ 3 H] l -arginine to [ 3 H] l -citrulline. Electron micrography demonstrated that endothelial cell ultrastructure but not vascular smooth muscle cell ultrastructure was abnormal after incubation of rings for 24 hours with 100 μmol/L carbenoxolone. These studies suggest that carbenoxolone concentrations higher than 10 μmol/L enhance vasoconstrictor action via selective toxicity to the endothelium and elimination of endothelium-dependent relaxation.