Influence of tracheal muscular tone on the initiation of cough reflex.

We devised a canine blood-perfusion preparation which made feasible administration of drugs directly at the local tracheal site. The hypothesis of Salem and Aviado on cough mechanism that a local airway constriction induced by stimuli may be a trigger in stimulating cough receptors was investigated using this preparation. Close intraarterial injections of acetylcholine (ACh) and histamine did not elicit a cough although intense tracheal constrictions were evident. The cough reflex elicited by electrical stimulation of the mucosa of isolated upper trachea in situ was accompanied by a slight systemic hypotension, tracheal vasodilatation and tracheal muscular constriction. The latter two changes occurred after a time lag following coughs. Close intraarterial infusions of isoproterenol and papaverine caused a prominent tracheal dilatation, but did not suppress the coughs. Pretreatment with atropine sufficiently inhibited cholinergic tracheoconstriction but had no effect on the electrically induced coughs. Furthermore, an augmentation of the tracheal muscular tone produced by an infusion of ACh did not enhance the cough reflex. In light of our observations, the aforementioned hypothesis should be reconsidered.