Bronchodilatation: noncholinergic, nonadrenergic mediation demonstrated in vivo in the cat

The composite vagus nerve was stimulated during intravenous infusion of 5-hydroxytryptamine in cats subjected to pharmacologic autonomic blockade with atropine, propranolol, and phentolamine. Bronchial caliber, as assessed by changes in pulmonary resistance, demonstrated a marked dilatation, and dilatation could still be demonstrated after preliminary treatment with reserpine. By stimulating the component branches of the vagus nerve, it was determined that the parasympathetic branch is responsible for this phenomenon.