The ganglion blocking and vagolytic actions of three short-acting neuromuscular blocking drugs in the cat

Abstract

Three recently-introduced short-acting neuromuscular blocking drugs with non-depolarizing mechanisms of action, stercuronium, dacuronium and AH8165 (1,1′-azobis [3-methyl-2-phenyl-1H-imidazo (1, 2a) pyridinium] dibromide) have been tested in the anaesthetized cat on the responses of the nictitating membrane to stimulation of the cervical nerve, and of the heart to vagal stimulation. The effects of the three drugs at the superior cervical ganglion and at the cardiac neuroeffector junction have been compared with their neuromuscular blocking effects. At doses lower than those required to block neuromuscular transmission all three compounds possessed a selective atropine-like action at the cardiac vagus neuroeffector junction in that they inhibited the bradycardia produced by vagal stimulation and by acetyl-β-methylcholine, whilst the depressor action of acetyl-β-methylcholine was unaffected. The ratios of the doses of the drugs to block the responses of the preganglionically-stimulated nictitating membrane and of the tibialis anterior muscle were 16̇7 for stercuronium, 8̇5 for dacuronium and 3̇8 for AH8165. The greater ganglion-blocking activity of AH8165 was reflected in the depressor action of the compound, whereas the weak ganglion-blocking actions of stercuronium and dacuronium were insufficient to mask the tachycardia and pressor effect caused by their blocking action on the cardiac vagus neuroeffector junction.