Antagonistic effect of Mandevilla velutina extract on kinin-induced contractions of guinea-pig and cat ileum longitudinal smooth muscle.

1. The effect of aqueous/alcoholic extract of Mandevilla velutina on bradykinin (BK), lysyl-bradykinin (L-BK), methionyl-lysyl-bradykinin (M-L-BK), acetylcholine (Ach) and histamine (Hist)-induced contractions in the isolated muscle from guinea-pig and cat ileum was analysed. 2. In the presence of atropine and pyrilamine, the extract (0.5-2 mg/ml) caused a parallel and concentration-dependent rightward displacement to all three kinins dose-response curves. Schild plots yielded nominal PA2 values (g/ml) of 3.2, 3.3 and 3.8 respectively, but the slopes of BK and M-L-BK were different from unity. 3. M. velutina extract (1 and 2 mg/ml) also concentration-dependently inhibited the contractile response evoked by BK in the isolated cat ileum and produced only slight depressions of the Ach and His-contractions (less than 20%) suggesting some selectivity towards kinin receptors. 4. These findings and those previously reported indicate that the active principles present in the crude extract of M. velutina competitively antagonizes kinin-induced contractions in several smooth muscle preparations.