Local anaesthetics inhibit cholinergic and non-cholinergic neural and muscular contractions in avian tracheal smooth muscle.

The effects of five different local anaesthetics: lignocaine, prilocaine, etidocaine, mepivacaine, bupivacaine, on tone, contractility, and on cholinergic and non-cholinergic responses of chick tracheal smooth muscle were studied and compared in vitro. The cholinergic and non-cholinergic contractions of the tracheal smooth muscle were elicited by electrical field stimulation, at a maximal voltage with 0.2 Hz and 0.2 ms square pulse duration, in the presence of adrenergic blockers, guanethidine, propranolol, and other drugs, e.g. indomethacin. Atropine was used to reduce the cholinergic responses due to electrical field stimulation and to applied acetylcholine (ACh). Lignocaine, in low concentrations, reduced these responses and also those produced by electrical field stimulation in the presence of atropine. In high concentration (greater than 100 times clinical concentrations), lignocaine abolished all the responses and produced a sustained contracture in the muscle. Among the local anaesthetics studied, bupivacaine and lignocaine were found to be more effective than mepivacaine, prilocaine and etidocaine, in reducing the cholinergic contractions produced by electrical field stimulation and by exogenous ACh. It was suggested that lignocaine, and other local anaesthetic drugs, may have an anti-spasmic effect on the tracheal smooth muscle, in that they inhibited the contractions induced by electrical field stimulation and by depolarizing agents.