Characterization of nicotine-induced contraction in the canine bronchus

1. The modes of action of nicotine on the dog bronchial smooth muscle preparation was investigated, in order to compare with those on the bronchial preparations from the guinea-pig, rabbit and monkey. 2. Nicotine induced a contraction in the dog bronchial preparation, and this response was abolished by hexamethonium and atropine and potentiated by physostigmine. 3. These findings suggest that the contractile response to nicotine was mediated through an action on the nicotinic receptors and due to the release of acetylcholine. 4. Tetrodotoxin did not inhibit the contractile response to nicotine in the dog bronchial preparation, suggesting that the nicotine-induced response may be produced mainly through a sodium action potential-independent process. 5. The present observations in the dog bronchial preparations coincided with those in the rabbit and monkey bronchi but not with the findings in the guinea-pig bronchus.