Nitric oxide mediated endothelium-dependent relaxation induced by glibenclamide in rat isolated aorta.

TLDR: Results indicate that glibenclamide-induced endothelium-dependent relaxation involves nitric oxide release and this effect may be related to its stimulatory effect on endothelial Ca(2+) levels and on the protein kinase C-mediated contractile mechanism.

Abstract: Objectives: Glibenclamide was found to act as both a selective ATP-sensitive K+ channel blocker and a vasorelaxant. The exact mechanisms underlying the relaxant effect of glibenclamide are unknown. The present study was designed to examine the role of endothelium/nitric oxide in glibenclamide-induced relaxation in rat isolated aortic rings. Methods: A combination of experimental approaches including isometric force measurement, cell culture, Ca2+ fluorescence measurement and radioimmunoassay were used to examine the vascular effect of glibenclamide. Results: Glibenclamide induced a concentration-dependent relaxation more effectively in rings with endothelium (IC50 of 32±4 μM) than those without endothelium (IC50 of 365±29 μM). Incubation with N G-nitro-l-arginine methyl ester (L-NAME) or methylene blue significantly reduced and l-arginine (3 mM) potentiated the glibenclamide-induced relaxation. l-Arginine (3 mM) partially antagonized the effect of L-NAME. Glibenclamide (100 μM) increased the cyclic GMP content of endothelium-intact tissues. Pretreatment with N G-nitro-l-arginine (100 μM) or removal of endothelium significantly suppressed the effect of glibenclamide on cyclic GMP production. Glibenclamide elevated the intracellular Ca2+ levels in cultured rat aortic endothelial cells. Glibenclamide also inhibited the endothelium-independent contractile response to 60 mM K+ (IC50 of 137±21 μM) and caused a rightward shift in the concentration–contraction curve for CaCl2. Besides, glibenclamide inhibited phorbol-12,13-diacetate (1 μM)-induced contraction in Ca2+-free Krebs solution. Conclusion: These results indicate that glibenclamide-induced endothelium-dependent relaxation involves nitric oxide release and this effect may be related to its stimulatory effect on endothelial Ca2+ levels. However, the glibenclamide-induced endothelium-independent relaxation may be associated with its inhibitory effect on Ca2+ influx through Ca2+ channels and on the protein kinase C-mediated contractile mechanism.