Skeletal Muscle Relaxants in the Root Extract of Rauvolfia cumminsii

Abstract

A crude extract from R. Cumminsii roots produced skeletal muscle relaxation in rats following intraperitoneal (i.p.) administration. This was assessed by the “Pull-up” time test. The extract, at all concentrations tested, produced a prolongation of the “pull-up” time that was interpreted as being due to the relaxant effect of the extract. When compared with standard skeletal muscle relaxant drugs such as chlorodiapoxide (20 mg/kg, i.p.), diazepam (40 mg/kg, i.p.) and dantrolene sodium (30 mg/kg, oral), the root extract (200–1000 mg/kg, i.p.) proved to be a more effective. In vitro studies using isolated rat phrenic nerve-diaphragm preparations revealed the extract (2.5–100 µg/ml) had no effect on the twitch tension elicited by direct stimulation of the diaphragm muscle, but caused a dose-dependent reduction of neurally evoked twitches. The inhibitory effect of the root extract on twitch tension was exacerbated by decamethonium (1 µM) and antagonized by both physostigmine (2 µM) and guanidine (0.1 mM). From these results, we suggest that the root extract produces skeletal muscle relaxation by causing a prejunctional block of neuromuscular transmission in the rat.