Relaxation by sevoflurane, desflurane and halothane in the isolated guinea-pig trachea via inhibition of cholinergic neurotransmission

We have studied relaxation of airway smooth muscle by sevoflurane,desflurane and halothane in the isolated guinea-pig trachea. Ringpreparations were mounted in tissue baths filled with physiological saltsolution (PSS), aerated continuously with 5% carbon dioxide in oxygen.Electrical field stimulation (EFS) elicited cholinergic contractions thatwere abolished by tetrodotoxin, indicating nerve- mediated responses.Anaesthetics were added to the gas aerating the tissue baths. Halothane,sevoflurane and desflurane at 0.5-1.0 MAC markedly attenuated cholinergiccontractions to EFS. Initiation of contractile responses to acetylcholine(ACh) were not affected by volatile anaesthetics, suggesting prejunctionalinhibition (i.e. inhibition of acetylcholine release). When added to amaintained submaximal contraction to ACh, volatile anaesthetics inducedrelaxation, indicating postjunctional inhibition. We conclude thatsevoflurane, desflurane and halothane inhibited postganglionic cholinergicneuroeffector transmission in the trachea. The effect was probably exertedvia pre- and postjunctional mechanisms (i.e. inhibition of acetylcholinerelease and direct muscle actions). Sevoflurane and desflurane were morepotent than halothane both pre- and postjunctionally.