ABSTRACT
The grape leaf [Vitis vinifera] has been used traditionally to treat diarrhea. We have recently showed that the grape leaf extract induces relaxation in rat aorta, vas deferens, and uterus. The vasorelaxatory effect on aorta was mostly dependent on endothelium, and the NO was involved; but in uterus and vas deferens, the relaxatory effect was dependent on voltage dependent calcium channels. The aim of the present study was to investigate the effect of grape leaf hydroalcoholic extract on rat colon contractions induced by some spasmogens and its mechanism[s]. Extract was prepared by the macerated method using 70% alcohol for 72 h, and the solvent was then evaporated. In a male adult Sprague Dawley rat anaesthetized by ether and after laparatomy, two pieces [1 cm] of distal colon was removed. In an organ bath containing Tyrode solution, colon was mounted and an isotonic transducer under 1 g resting tension recorded the contractions. In the separate protocols, KCl [60 mM], BaCl[2] [4 mM], acetylcholine [1 microM] induced contraction and extract was added to organ bath [0.5, 1,2 and 4 mg/ml] cumulatively. The results showed that Vitis vinifera leaf hydroalcoholic extract [VLHE] reduces contractions induced by these spasmogens [n=7, p<0.0001] and in a dose dependent manner. The spasmolytic effect of VLHE on ACh-induced contraction was unaffected by propranolol as the beta-adrenoceptor antagonist [1 microM, for 30 min], L-NAME as a nitric oxide synthase inhibitor [300 microM, for 30 min]. Neither phentolamine as the non-selective alpha-adrenoceptor antagonist [1 microM, for 30 min] nor naloxone [opioid antagonist, 1 microM, for 30 min] was ineffective on VLHE spasmolytic activity. Blocking the ATP-dependent potassium channels by glibenclamide [3 microM, for 30 min] had no effect on the extract spasmolytic activity. But adding tetraethylammonium [TEA, 5 mM] to the extract-induced relaxation, caused colon contraction. These results suggest that the VLHE spasmolytic effect is due, at least in part, to blockade of the voltage dependent calcium channels. The calcium dependent potassium channels are also involved. Furthermore, alpha and beta-adrenergic, NO and opioid receptors were not involved