Effects of Mondia whitei extracts on the contractile responses of isolated rat vas deferens to potassium chloride and adrenaline

摘要

Objective: To investigate the effects of the methylene chloride:methanol (CH_2CI_2:MeOH, 1:1) extract of the dried roots of Mondia whitei Linn and its hexane and methanol fractions on potassium chloride (KCI) and adrenaline (Adr)-induced contractions of rat vas deferens. Materials and Methods: Isolated strips of normal adult rat vas deferens were mounted in a Ugo Basile single-organ bath containing Krebs solution. Cumulative concentration-response curves of KCI (1-7 x 10~2 M) and adrenaline (1 21-8.45 x 10~(-7) /M were established in the absence and presence of M. whitei (50-400 mug/ml). In separate experiments, after obtaining a stable plateau of contractions with KCI (60 mM), M, whitei samples (50-400 mug/ml) were added cumulatively to relax the preparation. In KCI (60 mM), containing depolarizing medium, cumulative concentration-contraction curve to CaCI_2 (2-14 x 10~(-2) M) was elicited in the absence and presence of the hexane fraction of M. whitei (50-400 mug/ml). Results: All the M. whitei samples produced rightward shift of the concentration-response curves to KCI and Adr. At high concentration of the plant extracts (400 mug/ml), a decrease of the maximal response to the contractile agents was observed compared with that obtained with the control. All the three extracts produced concentration-dependent relaxation of the plateau of contraction induced by KCI and the hexane fraction appeared to be the more potent. In calcium-free physiological salt solution, the hexane fraction of M. whitei produced rightward shift to the concentration-response curve to CaCl_2 and completely abolished the contractile effect of calcium at high concentration (400 mug/ml). Conclusion: It is concluded that M. whitei extracts antagonized the contractile responses to KCI and Adr in isolated rat vas deferens, which could be due to the blockade of voltage-operated calcium channels.