Inhibition of the vagal reflex-induced tracheal constriction by psychotropic drugs.

We investigated the effects of psychotropic drugs on reflex tracheal constriction in anesthetized, paralyzed, and artificially ventilated mongrel dogs. The tracheal constriction induced by the electrical stimulation of the central cut end of the right vagus nerve was abolished by sectioning both the left superior laryngeal and recurrent laryngeal nerves, and was reduced by a low dose of pentobarbital (3 mg/kg, i.v.). This indicates that the tracheal constriction is mediated by a vagal reflex. Chlorpromazine (3 mg/kg, i.v.) and imipramine (1-3 mg/kg) reduced the reflex tracheal constriction. Chlorpromazine and imipramine had no effect on the tracheal constriction induced by the efferent electrical stimulation of the recurrent laryngeal nerve. This suggests that the higher centers may affect the reflex airway constriction and that the present preparation may be useful for investigating the effect of psychotropic drugs on the reflex airway constriction during asthmatic attacks.