A Pharmacological Comparison of Strychnos Guianensis and Curare Compounds on the Neuromuscular Transmission

Usually a moderately-sized liane, Slrychnos giiianemis (Aubl.) Martius occurs in forests, more especially along creeks and small rivers throughout thé middle and upper Rio Orinoco basin and entire Amazon basin (1). Among thé plants of thé Strychnos genus, this Slrychnos is known to be one of thé principal ingrédients of thé curare produced by numerous Indian tribes. This species contains a group of peculiar alkaloids characterized by their bright orange colour which becomes green-blue when sprayed with sulphate ceric. Our study was carried out to compare thé activity of thé crude quaternary alkaloids with other curare compounds or référence substances and to quantify it. The crude quaternary alkaloids extract was injected intravenously in rats (jugular vein) whose médium wheight was 250 g. An inhibitory effect on thé neuromuscular transmission (sciaticgastrocnemius) was observed. The amount required to produce a complète inhibition ranged from 8 to 12 mg/kg.This dose doesn't classify Strychnos guianensis among thé very strong curares (2). However, preliminary observations suggest that, thé rat, maintained alive by respiratory assistance, doesn't recover thé neuromuscular transmission in spite of repeated injections of a cholinesterases inhibitor (physostigmine) (3). Other référence curares were tested in thé same expérimental conditions. The amounts required for a total inhibition were weaker and their effècts reversed by physostigmine (Table 1). In conclusion, thé crude quaternary alkaloids extract of Slrychnos guianensis showed a pronounced muscle-relaxant activity in vivo which was not antagonized by physostigmine. So, it appears that Strychnos guianensis alkaloids operate by a différent mechanism from that of bis-quaternary alkaloids of Strychnos toxifera (Calabash) which act by compétition with acetylcholine for thé nicotinic receptors. Future works will probably allow to elucidate thé mechanism of action of this crude quaternary extract and to identify thé main active principles of thé plant.