Carbenoxolone damages endothelium and enhances vasoconstrictor action in aortic rings

Carbenoxolone causes hypertension indirectly by inhibition of 11 beta-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 mu mol/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 mu mol/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 of ATP was reduced by more than 90% by 24-hour pretreatment with 100 mu mol/L carbenoxolone but not with 100 mu mol/L deoxycorticosterone acetate (a mineralocorticoid) or 100 mu mol/L glycyrrhizic acid (a natural 11 beta-hydroxysteroid dehydrogenase inhibitor). Vascular smooth muscle relaxation with sodium nitroprusside was not inhibited by carbenoxolone. Incubation of cultured endothelial cells with 100 mu mol/L carbenoxolone for 24 hours did not inhibit nitric oxide synthase activity, as measured by conversion of [H-3]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 mu mol/L carbenoxolone. These studies suggest that carbenoxolone concentrations higher than 10 mu mol/L enhance vasoconstrictor action via selective toxicity to the endothelium and elimination of endothelium-dependent relaxation.