Objective: To investigate the effects of the methylene chloride:methanol (CH2Cl2:MeOH, 1:1) extract of the dried roots of Mondia whitei Linn and its hexane and methanol fractions on potassium chloride (KCl) 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 KCl (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 µg/ml). In separate experiments, after obtaining a stable plateau of contractions with KCl (60 m M ), M. whitei samples (50-400 µg/ml) were added cumulatively to relax the preparation. In KCl (60 m M ), containing depolarizing medium, cumulative concentration-contraction curve to CaCl2 (2-14 x 10-2 M ) was elicited in the absence and presence of the hexane fraction of M. whitei (50-400 µg/ml). Results: All the M. whitei samples produced rightward shift of the concentration-response curves to KCl and Adr. At high concentration of the plant extracts (400 µg/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 KCl 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 CaCl2 and completely abolished the contractile effect of calcium at high concentration (400 µg/ml). Conclusion: It is concluded that M. whitei extracts antagonized the contractile responses to KCl and Adr in isolated rat vas deferens, which could be due to the blockade of voltage-operated calcium channels.
