PHARMACOLOGICAL STUDIES ON RAUWOLFIA VERTICILLATA(LOUR.)BAILL.PRODUCED IN YUNNAN PROVINCE Ⅰ.HYPOTENSIVE ACTION AND ITS MECHANISM

The alkaloid (named verticilloid) of Rauwolfia verticillata (Lour.) Baill. was isolated by Kunming Pharmaceutical Factory of Yunnan province. The present paper reports the experimental results on its hypotensive action and the mechanism involved. 1.Verticilloid produced a hypotensive effect on urethan-anesthetized cats. In intravenous injections at the dosage of 3 mg/kg it produced a prompt fall of arterial blood pressure of about 53%, and lasted for about 8 hours. A second administration of the drug at the same dose showed tachyphylaxis. 2.During the fall of the blood pressure after verticilloid administration, there was no significant change in heart beat. A dose of 3—6 mg/kg given intravenously caused a shortening of the R—R, PR and QT intervals of the EKG of anethetized cats. 3.The respiratory amplitude was increased slightly during the early phase of the fall of blood pressure in all anesthetized cats. The respiratory rate was increased in most cases at the time when the blood pressure was at its lowest. The respiration rate recovered only gradually. 4.In perfused isolated rabbit's ears whose hind legs and legs with the innervation were kept intact. verticilloid showed no direct vasodilating effect. 5.Verticilloid inhibited the pressor responses to electrical stimulation of the afferent vagi and tibial nerves and also the carotid occlusion pressor reflex. The hypotensive effect was not eliminated by atropinisation or vagotomy. Verticilloid caused inhibition and sometimes reversal of the pressor response to injected adrenaline. 6.The LD₅₀ after oral administration of the drug was found to be 870 mg/kg for mice, the chief symptom before death was dyspnea.