study on mechanism of vasorelaxatory effect of vitis vinifera leaf extract in rat aorta

introduction: our previous studies showed that hydroalcoholic extract of leaf of vitis vinifera relaxes the phenylephrine-induced contraction in rat thoracic aorta. this effect was dependent on endothelial integrity and no-cgmp system. the vasorelaxant effect of extract was much lesser on kcl-induced contraction. we, therefore, postulated that k+ channels are involved. the main aim of the present study was to determine the type of k+ channels involved in this vasorelaxant effect. methods: thoracic aorta with intact endothelium was removed from adult male wistar rats (170-220g). the aorta was mounted in an organ bath containing krebs-henseleit (37 ºc, ph 7.4) bubbled with o2. aortic contractions were recorded isometrically under 1 g resting tension. the aorta endothelium was considered intact if acetylcholine (1 μm) could induce more than 70% aorta relaxation on 1μm phenylephrine-induced contraction. extract was prepared by maceration method using 70% alcohol and the solvent was then evaporated. results: the results showed that in the presence of tetraethylammonium (10 mm), the vasorelaxant effect of extract (0.25, 0.5, 1 and 2 mg/ml) was reduced (p<0.001, n=7). in contrast, glibenclamide (1 μm) had no effect. in calcium-free (plus 0.1 mm of edta) krebs-henseleit solution, the vasorelaxant effect of extract (0.25, 0.5 and 1 mg/ml) was reduced (p<0.0001, n=8). furthermore, the vasorelaxant effect of extract was unaffected by indomethacin (1 μm). conclusion: these results suggest that vitis vinifera leaf hydroalcoholic extract induces relaxation in rat aorta possibly by opening the ca2+ -operated k+ channels but, not atp- sensitive k+ channels and extracellular calcium was essential for inducing vasorelaxation by extract. furthermore, cyclooxigenase was not involved in this vasorelaxant effect.