Intravenous versus inhaled atropine for inhibiting bronchoconstrictor responses in dogs

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Abstract
Whether the muscarinic antagonist, atropine, given i.v. or by inhalation, inhibits the bronchoconstrictor responses to inhaled acetylcholine, and to acetylcholine released by electrical stimulation of the vagus nerves to the same degree was studied. Bronchoconstrictor responses wre assessed in anesthetized dogs by determining the increase in total pulmonary resistance before and after increasing doses of atropine and then constructing inhibition dose-response curves. Before atropine, the responses to the 2 stimuli were equal in magnitude. After i.v. atropine (initial dose 0.12 .mu.g/kg, total dose 16 .mu.g/kg) both responses were progressively inhibited to similar degree. After inhaled atropine (initial dose 0.02 .mu.g/kg, total dose 2.4 .mu.g/kg), the response to acetylcholine inhalation was inhibited to a much greater degree than the response to vagal stimulation. In studies designed to inhibit bronchoconstriction due to an inhaled muscarinic agonist to the same degree as bronchoconstriction due to a vagal reflex, atropine might better be given i.v. than by inhalation.