Do Pipecuronium and Rocuronium Affect Human Bronchial Smooth Muscle? 

Background Muscle relaxants affect nicotinic and muscarinic receptors. Interaction of muscle relaxants with muscarinic receptors of human airways has been studied incompletely. Methods The effects of pipecuronium bromide (long-acting, nondepolarizing) and rocuronium bromide (intermediate-acting, nondepolarizing) on prejunctional and postjunctional muscarinic receptors were studied in 96 isolated human bronchial rings from 12 patients. Contractile isometric responses to electric field stimulation of pilocarpine-stimulated and nonstimulated M2 muscarinic receptors were compared before and after incubation with the two muscle relaxants. The effect on postjunctional muscarinic receptors was studied by comparing acetylcholine concentration-response curves before and after incubation with the two muscle relaxants. Results Pipecuronium bromide, but not rocuronium bromide, inhibited pilocarpine-stimulated prejunctional M2 muscarinic receptors. Neither pipecuronium bromide nor rocuronium bromide had significant inhibitory effects on nonstimulated M2 muscarinic receptors and on postjunctional M3 muscarinic receptors. Conclusions The inhibitory effect of pipecuronium bromide on pilocarpine-stimulated prejunctional M2 muscarinic receptors occurred at clinical concentrations.