PHARMACOLOGICAL STUDIES OF LYCORENINE, AN ALKALOID OF LYCORIS RADIATA HERB.: VASODEPRESSOR MECHANISM IN RATS

Vasodepressor mechanism of lycorenine (an alkaloid of Lycoris radiata Herb.) was investigated in anesthetized rats. Lycorenine (1-10 mg/kg i.v.) produced dose-related decreases in blood pressure and heart rate and tachyphylaxis developed with repeated injections. In the blood-perfused rat hindquarters, lycorenine (62.5- 500 pg i.a.) produced dose-related decreases both in mean blood pressure and in perfusion pressure, and the lycorenine-induced decrease in perfusion pressure was abolished by phenoxybenzamine or hexamOthonium. Lycorenine (more than 1 mg/kg i.v.) blocked the pressor response to sympathetic nerve stimulation, but failed to block the tachycardia induced by sympathetic nerve stimulation. Lycorenine (7.5 or 15 mg/kg i.v.) reduced the spontaneous splanchnic nerve activity. Lycorenine when given intracerebroventricularly produced decreases in blood pressure and heart rate only in large doses (over 500 /μg). The maximal bradycardia induced by lycorenine was abolished by bilateral vagotomy. It is suggested that lycorenine may produce a decrease in blood pressure as the result of alpha-adrenergic blockade in conjunction with the reduction of the spontaneous sympathetic nerve activity, and produce bradycardia by modifying vagal activity.