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 micrograms 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 hexamethonium. 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 micrograms). 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.