Neuromuscular blocking and ganglion blocking activities of some acetylcholine antagonists in the cat

Abstract

The potencies of tubocurarine, gallamine, pancuronium, benzoquinonium, hexamethonium and mecamylamine in blocking neuromuscular transmission in the soleus muscle, and in blocking contractions of the nictitating membrane evoked by preganglionic sympathetic stimulation have been compared in cats under chloralose anaesthesia. On a molar basis, pancuronium was about 8 times and benzoquinonium about 2·5 times more potent than tubocurarine in blocking the soleus muscle; gallamine was less than half as potent, mecamylamine about 128 times and hexamethonium about 380 times less potent. In blocking the superior cervical ganglion, mecamylamine was about 17 times more, tubocurarine was about 5 times more and pancuronium about twice as potent as hexamethonium. Benzoquinonium was about half as potent as hexamethonium, and gallamine about 5 times less potent. The results emphasize that the shorter distance between charged centres, as in hexamethonium, reduces affinity for muscle receptors but does not necessarily enhance affinity for ganglion receptors, and from the point of view of deductions concerning the configuration of the ganglionic receptor, the ganglion blocking potencies of some neuromuscular blocking drugs should be taken into account.