The selective antimuscarinic action of stercuronium

1 The antimuscarinic activity of stercuronium, a competitive neuromuscular blocking drug, has been compared in the anaesthetized guinea-pig, guinea-pig atria, bladder and ileum, rabbit atria and the sympathetically innervated rabbit ear artery preparation using carbachol (CCh) as agonist.2 In the anaesthetized guinea-pig, stercuronium (0.2 and 2.0 mumol/kg) produced significantly greater inhibition (P < 0.05) of the bradycardia than of the vasodepressor response produced by CCh, the difference being 2 fold at the low dose and 5.8 fold at the higher dose.3 In guinea-pig atria the negative chronotropic response to CCh was inhibited to a similar degree to the negative inotropic response by stercuronium, whereas in bladder and ileum stercuronium was 17 fold less active as an antimuscarinic drug.4 The affinity of stercuronium for the prejunctional muscarinic receptor on sympathetic nerve endings in the rabbit ear artery was similar to that for the muscarinic receptor mediating negative inotropic responses to CCh in the rabbit left atrium, and 2.3 fold less than the affinity for the muscarinic receptors in guinea-pig atria.5 A similar trend was observed with gallamine, another neuromuscular blocking drug, when results obtained in the rabbit ear artery preparation were compared to previously reported data. Also, the affinity of gallamine for muscarinic receptors mediating relaxation of the cat anococcygeus muscle was found to be similar to that for prejunctional muscarinic receptors in the rabbit ear artery.6 It is suggested that stercuronium and gallamine have a greater affinity for cardiac receptors and the inhibitory muscarinic receptors on sympathetic nerve endings than for muscarinic receptors mediating contraction of bladder and ileum.