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

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We investigated the involvements of sympathetic and nonadrenergic nervous systems in the inhibitory reflex following bronchoconstriction in dogs. Inhalations of a 0.00125% solution of histamine and <I>Ascaris suum</I> antigen (3 mg protein) to the bronchial side induced reflex tracheal constriction following bronchoconstriction. An intra-arterial infusion of 5 μg/min of atropine to the tracheal site changed the reflex tracheal constrictions by histamine and antigen inhalations into tracheal dilatations. The reflex tracheal dilatations were abolished by the combination of intra-arterial propranolol (100 μg) and transections of both the bilateral superior laryngeal nerves and the spinal cord at the C<SUB>1</SUB> level. The reflex tracheal constrictions induced by histamine and antigen inhalations were increased with 100 μg propranolol. Furthermore, the reflex tracheal constrictions were enhanced by the combination of 100 μg 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 response may be mainly mediated by the sympathetic nerves, with partial involvement of the nonadrenergic nerves. This inhibitory reflex may attenuate asthmatic broncho-constriction.