title: The role of the parasympathetic system in the regulation of bronchial smooth muscle.
abstract: The possibility that bronchial hyperreactivity, a consistent feature of asthma, is due to an exaggeration of activity in parasympathetic reflex pathways altering airway smooth muscle tone is suggested by the facts that virtually all asthmatic subjects have exaggerated bronchomotor sensitivity to muscarinic agonists and that muscarinic antagonists are effective bronchodilators. Studies of the effects of atropine, a postganglionic cholinergic (muscarinic) antagonist, and of hexamethonium, a drug which occupies ganglionic receptor sites, suggest that bronchial hyperreactivity is associated with an increase in postganglionic cholinergic sensitivity. This hypothesis is supported by the demonstration of dose-dependency of an antimuscarinic agent in inhibiting the bronchomotor response to eucapnic hyperpnea (at 75 l/min) with cold air. Greater doses of a muscarinic antagonist were needed to inhibit the response to cold air than were needed to alter baseline airway caliber or to inhibit the response to a muscarinic agonist given by aerosol.
mesh_terms: D000403:Airway Resistance / Q000187:drug effects; D001249:Asthma / Q000188:drug therapy / Q000503:physiopathology*; D001285:Atropine / Q000494:pharmacology; D001980:Bronchi / Q000294:innervation*; D001993:Bronchodilator Agents / Q000627:therapeutic use; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D006801:Humans; D009130:Muscle, Smooth / Q000294:innervation*; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010277:Parasympathomimetics / Q000627:therapeutic use
chemical_list: D001993:Bronchodilator Agents; D006584:Hexamethonium Compounds; D010277:Parasympathomimetics; D018738:Hexamethonium; D001285:Atropine