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Abstract
The effect of crude saponins of Castanospermum australe (CA) was studied in anesthetized rats and on isolated tissue preparations. The results showed that CA in the dose range of 1-30 mg/kg produced a fall in blood pressure and heart rate in normotensive anesthetized rats. Pretreatment of animals with atropine (2 mg/kg) abolished both hypotensive and bradycardiac effects of CA. In isolated guinea-pig atria, CA produced negative inotropic and chronotropic responses at 100-1000 μg/mL. When tested on isolated guinea-pig ileum, it produced contractile responses similar to those of acetylcholine (ACh). All these responses of CA and ACh on cardiac and smooth muscle preparations were completely blocked by atropine (0.1 μg/ml). These data indicate that the crude saponins from Castanospermum australe mediate all their effects through a mechanism similar to that of acetylcholine.