The Contractile Effect of Ethanolic Extract of West African Black Pepper (<i>Piper guineense</i>) on Isolated Guinea Pig Ileum

The effect of ethanolic extract of West African black pepper ( Piper guineense ) on contractility of gastrointestinal smooth muscle was studied by muscle-bath contractility method using isolated Guinea pig ileum. The effective dose range of the extract on the ileum was determined by the concentration of the extract at the threshold and maximal contractile responses. The dose-response curve for the effect of the extract alone on the strips of isolated ileum and for the extract in the presence of 1x10 -5 M atropine, 1x10 -5 M pyrilamine and 1x10 -5 M cimetidine were obtained. Evaluation of the potency (EC 50 ), affinity (pA 2 ) of the extract and the maximal response (Emax) to the extract were determined in absence (control) and presence of each antagonist (test). Statistical test of the significance of differences of the means between control and test groups was established using the Student`s t-test at p<0.05. P. guineense contracted the smooth muscle of ileum of guinea pig in a dose-dependent manner. The threshold value for the contraction was 0.9mg mL -1 while the maximal response was obtained at a concentration of 3.6mg mL -1 of extract solution. P. guineense -induced contraction was modified by atropine (cholinergic antagonist), pyrilamine (H 1 -receptor antagonist) and cimetidine (H 2 -receptor antagonist). The three antagonists caused a right-ward shift on the dose-response curve and the maximal contractile response of the ileal strips to the extract was attainable in the presence of the antagonists suggesting that atropine, pyrilamine and cimetidine inhibited the effect of the extract competitively. The potency and affinity of the extract were significantly reduced by 1x10 -5 M atropine, 1x10 -5 M pyrilamine and 1x10 -5 M cimetidine. While atropine and pyrilamine did not significantly modify the maximal response, cimetidine significantly depressed the maximal contractile response of ileum to the ethanolic extract of P. guineense . The findings in this study strongly suggest that M cholinergic, H 1 and H 2 receptors are involved in the pharmacodynamics of P. guineense -induced contraction of gastrointestinal smooth muscle.