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 non-stimulated M 2 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 M 2 muscarinic receptors. Neither pipecuronium bromide nor rocuronium bromide had significant inhibitory effects on nonstimulated M 2 muscarinic receptors and on postjunctional M 3 muscarinic receptors. Conclusions: The inhibitory effect of pipecuronium bromide on pilocarpine-stimulated prejunctional M 2 muscarinic receptors occurred at clinical concentrations.