ABSTRACT
Reports have shown the antioxidant, hypotensive, hypolipidemic and vasodilatory effects of grape [Vitis vinifera L.] seed extract. We have recently shown the relaxatory effect of grape leaf extract on rat uterus and reduction of frog heart rate and contractility. The aim of the present study was to investigate the relaxant effect of Vitis vinifera leaf hydroalcoholic extract [VLHE] on rat thoracic aorta contractions induced by phenylephrine and KCl and the role of aorta endothelium on this action. Rat aorta was removed and placed in an organ bath containing Krebs-Henseleit solution and aorta contractions were recorded isometrically. The results demonstrate that VLHE [0.125-2 mg/ml] reduces the endothelial intact aorta reconstructed by phenylephrine [1 micro M] dose-dependently [P<0.0001]. Extract induced the same response in endothelial denuded aorta, but in a much lesser extent. The IC50 for both groups were 0.45 +/- 0.08 and 1.73 +/- 0.23 mg/ml, respectively. However, the contractile responses of these groups were similar. VLHE [0.125-2 mg/ml] reduced the contractions induced by KCl [80 mM] dose-dependently [P<0.0001]. The relaxatory effect of VHLE on KCl_induced contractions was less than those evoked by Phenylephrine. Vasorelaxatory effect of VHLE on intact aorta was attenuated by nitric oxide synthase inhibitor [L-NAME, 100 microM] and gaunyl cyclase inhibitor [methylene blue, 10 microM] significantly, but was unaffected by atropine [1 microM]. The results suggest that the greatest vasorelaxant effect of VHLE on rat aorta is endothelium-dependent and nitric oxide [NO] and cGMP are mostly responsible but cholinergic receptors are not involved