In vitro modulating effects of glutathione on vascular tension and involvement of extracellular calcium

This study investigated the involvement of endothelium and extracellular calcium on the vasorelaxant activity of glutathione (GSH) using in vitro model of isolated rat aorta.The aortic tensions upon treatment with GSH in the presence and absence of endothelium were compared in various conditions. In phenylephrine-precontracted aortic rings, GSH (2-8 mM) significantly induced vasorelaxation in concentration-dependent manner. The influence of endothelium was demonstrated in determining the responses of aortic muscle toward GSH treatment. GSH (up to 5 mM) caused a higher loss of vascular tensions in the endothelium-intact aortic rings than those in the endothelium-denude preparations. The vasorelaxant effect of GSH in endotheliumintact rings was inhibited by glibenclamide (3 μM), methylene blue (10 μM) and N-nitro-L-arginine methyl ester (10 μM), indicating the involvement of membrane K+ channels and NO-cGMP pathway. In the endothelium-denude preparations, only glibenclamide inhibited the modulating effect of GSH on aortic tension. Furthermore, the endothelium-dependent vasorelaxation of GSH was abolished in Ca2+-free medium containing EGTA, but not in the medium containing BAPTA-AM (10 μM). Taken together, our findings suggested that vasorelaxant activity of GSH depended on influx of extracellular Ca2+ to activate NO production in endothelium cells. In addition, other possible mechanisms included its hyperpolarizing actions in vascular muscle cells.