Alpha-adrenergic receptor blocking effect of Cleistanthus collinus (Roxb.) Benth. and Hook f. leaf extract on guinea pig isolated smooth muscle preparations.

Aqueous extract of C. collinus leaves inhibited norepinephrine induced contraction in guinea pig vas deferens and aortic strip in a dose-dependent manner. Inhibition of acetylcholine induced contraction in ileum was dose independent. C. collinus extract per se had no effect on isolated guinea pig vas deferens and aortic strip, but inhibited norepinephrine induced contraction in a dose-dependent manner probably by its antagonist action on α-adrenergic receptor. It had inconsistent effect on guinea pig ileum in vitro preparation.