Analysis of the vagal reflex tracheal constriction in the dog

We devised a preparation for measuring the vagal reflex tracheal constriction following the bronchoconstriction induced by histamine inhaled in the bronchial side in dogs. Properties of the vagal reflex tracheal constriction were investigated using this preparation. Histamine inhaled in the bronchial side caused the tracheal constriction following the bronchoconstriction. The tracheal constriction was inhibited by section of the bilateral superior laryngeal nerves or vagal cooling, respectively, but was not completely blocked. The combination of section of the bilateral superior laryngeal nerves and vagal cooling abolished the tracheal constriction. An i.v. administration of pentobarbital reduced both bronchoconstriction and tracheal constriction. These findings indicate that the tracheal constriction observed in the present study is mediated by the vagal reflex arc and that the extravagal pathway consisting of the recurrent and superior laryngeal nerves plays a role in a part of the afferent pathway of the vagal reflex airway responses. When the bronchoconstriction was completely abolished by isoproterenol inhaled in the bronchial side, the reflex tracheal constriction still existed. Transient inflation and deflation of the lungs caused reflex tracheal dilatation and constriction, respectively. We conclude that the vagal reflex airway constriction is due to complex effects which may be mediated by plural sensory receptors in the airways.