A Note on the Pharmacology of the Alkaloids of Rauwolfia Serpentina Benth

Abstract

THE sedative and hypotensive properties of extracts of the root of Rauwolfia serpentina have been known in India for some time192, but have only relatively recently aroused interest in western clinical medicine374~5. The recent isolation of reserpinee (an alkaloid possessing these specific sedative and hypotensive properties) has clarified a somewhat confused picture of the nature and identity of the active principles.The precise mode of action of these active rauwolfia extracts and alkaloids is not yet known, and there is some confusion in the literature. The work of Plummer, Barrett, Wagle and Yonkman' indicates that, in the dog, the alkaloids have cholinergic properties. Beins has pointed out that in hypotensive doses, the drug did not act as a ganglionic blocking agent or as a sympatholytic. On the other hand, it potentiated the pressor actions of sympathomimetic amines. The hypotensive effects were not affected by atropine or vagotomy. It was suggested that there was a depression of the central portions of the sympathetic nervous system. Trapold, Osborne and Yonkmang divided the effects of reserpine into immediate and delayed actions. With respect to the latter, they confirmed much of the work of Bein; but they found that during the period of maximal hypotensive activity, there was potentiation of the effects of acetylcholine or vagal stimulation, and administration of adrenaline or noradrenaline produced the usual pressor response, coupled with bradycardia. Bradycardia and miosis caused by reserpine were antagonised by atropine. Gourzis, Sonnenschein and Bardenlo, working with a mixture containing the hypotensive and sedative principles of rauwolfia, point out that in the anaesthetised dog, there was potentiation of the pressor response to adrenaline ; the effects of afferent vagal stimulation were abolished ; but the hypotensive responses to acetylcholine, histamine and efferent vagal stimulation were not affected. There is a relatively long latent period before the sedative and hypotensive actions become apparent, even after intravenous injection'l. The reason for this is not clear.The genera Aspidosperma and Rauwolfia are closely related botanically and our interest and observations on the former12J3*14,15 led us to investigate some of the pharmacological properties of the alkaloids of the latter. We feel that our results may throw a little light on the mode of action of the Rauwolfia alkaloids.

Direct Effects of Reserpine, Rescinnamine and Canescine on Blood Vessels

“…Peculiar persistence of the effects of Rauwolfia alkaloids on isolated smooth muscle has been demonstrated by Bannerjee and Lewis (1955). The amounts of the alkaloids introduced in some of the present series of experiments were of the same order weight for weight (0' I milligramme per kilogram) as those which have been administered intravenously for therapeutic purposes (Hughes et alii, 1955).…”