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

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 rot 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 mon effectively in rings with endothelium (IC50 of 32+/-4 mu M) than those without endothelium (IC50 of 365+/-29 mu M). incubation with N-G-nitro-L-arginine methyl ester (L-NAME) or methylene blue significantly reduced and L-arginine (3 mM) potentiated the glibenelamide-induced relaxation. L-Arginine (3 mM) partially antagonized the effect of L-NAME. Glibenclamide (100 mu M) increased the cyclic GMP content of endothelium-intact tissues. Pretreatment with N-G-nitro-L-arginine (100 mu M) 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 mu M) and caused a rightward shift in the concentration-contraction curve for CaCl2. Besides, glibenclamide inhibited phorbul- 12,13-diacetate (1 mu M)-induced contraction in Ca2+-free Krebs solution. Conclusion: These results indicate that glibenclamide-induced endothelium-dependent relaxation involves nitric elude 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. (C) 2000 Elsevier Science B.V. All rights reserved.