Do pipecuronium and rocuronium affect human bronchial smooth muscle?

Background: Muscle relaxants affect nicotinic and muscarinic receptors, Int eraction 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 prejuncti onal and postjunctional muscarinic receptors were studied in 96 isolated hu man bronchial rings from 12 patients. Contractile isometric responses to el ectric field stimulation of pilocarpine-stimulated and nonstimulated M-2 mu scarinic receptors were compared before and after incubation with the two m uscle relaxants. The effect on postjunctional muscarinic receptors was stud ied by comparing acetylcholine concentration-response curves before and aft er incubation with the two muscle relaxants. Results: Pipecuronium bromide, but not rocuronium bromide, inhibited piloca rpipe-stimulated prejunctional M-2 muscarinic receptors, Neither pipecuroni um bromide nor rocuronium bromide had significant inhibitory effects on non stimulated M-2 muscarinic receptors and on postjunctional M-3 muscarinic re ceptors. Conclusions: The inhibitory effect of pipecuronium bromide on pilocarpine-s timulated prejunctional, M-2 muscarinic receptors occurred at clinical conc entrations.