Abstract-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 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 ,ag). 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 re duction of the spontaneous sympathetic nerve activity, and produce bradycardia by modifying vagal activity.Lycoris radiata Herb. is a poisonous plant which contains alkaloids such as lycorenine, lycorine, lycoramine, homolycorine, hippeastrine, galantamine, etc. We found a substance in the methanol-water extract of bulbs of Lycoris radiata Herb. which produced a decrease in blood pressure and with repeated injections tachyphylaxis developed to the vasodepressor effect in rats. This substance was identified as lycorenine. Although there are papers on the pharmacological effects of lycorine, lycoramine, and galanthamine among alkaloids of Lycoris radiata Herb., only one report on lycorenine (1) is available stating that this compound produced a decrease in blood pressure in dogs, cats, and rabbits, a transient increase of contractile force in the isolated toad heart, and an increase of motility of the isolated rabbit ileum. However, the mechanism of the vasodepressor action of lycorenine was not discussed. In the present study, the effects of lycorenine on the cardiovascular system and the autonomic nervous system were investigated in rats for elucidation of the vasodepressor mechanism. MATERIALS AND METHODSAnimals: Male Donryu rats, weighing 250-350 g, were used for cardiovascular studies.Female Donryu rats (200-250 g), male ICR mice (30-35 g), and male Hartley guinea-pigs

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Studies on Agents with Vasodilator and β-Blocking Activities. Part 1.-A series of hydrazinopyridazines, e.g. (VII) or (VIII), and hydrazinophthalazines, e.g. (IX), are synthesized in order to find superior vasodilators with β-blocking activity. Among (VII) derivative (VIIb) reveals the best hypotensive and β-blocking effects. -(SEKI, T.; TAKEZAKI, T.; OHUCHI, R.; OHUYABU, H.; ISHIMORI, T.; YASUDA, K.; Chem.