Inhibitory Reflex during Bronchoconstrictions Induced by Histamine and Ascaris Suum Antigen.

Abstract

ABSTRACT-We investigated the involvements of sympathetic and nonadrenergic nervous systems in the inhibitory reflex following bronchoconstriction in dogs. Inhala tions of a 0.00125% solution of histamine and Ascaris suum antigen (3 mg protein) to the bronchial side induced reflex tracheal constriction following bronchoconstriction. An intra-arterial infusion of 5 ug/min of atropine to the tracheal site changed the re flex tracheal constrictions by histamine and antigen inhalations into tracheal dilata tions. The reflex tracheal dilatations were abolished by the combination of intra-ar terial propranolol (100 ,ug) and transections of both the bilateral superior laryngeal nerves and the spinal cord at the C1 level. The reflex tracheal constrictions induced by histamine and antigen inhalations were increased with 100,ag propranolol. Further more, the reflex tracheal constrictions were enhanced by the combination of 100,ug propranolol and transection of the spinal cord. These findings indicate that during the constriction of the bronchial smooth muscle, not only a reflex tracheal constriction mechanism but also one of reflex dilatation operates and that the latter reflex re sponse may be mainly mediated by the sympathetic nerves, with partial involvement of the nonadrenergic nerves. This inhibitory reflex may attenuate asthmatic broncho constriction.