The Role of Bronchoconstriction in Cough Reflex

To investigate the role of bronchoconstriction in the cough reflex, we compared antitussive effects of several drugs with their ability to effect the respiratory tract (i.e. bronchodilatation vs. bronchoconstriction). Antitussive activities of five drugs administered either intravenously or orally on electrically-induced cough were evaluated in the non-anesthetized dog. The antitussive activities were as follows: morphine, 0.1 mg/kg (i.v.) and 0.5 mg/kg (p.o.); codeine, 1.0, 4.0; picoperidamine, 2.0, 9.8; piclobetol, 7.6, 9.0; HH-197, 12.5, 143.0, respectively. Morphine, codeine and HH-197 caused bronchoconstriction, but picoperidamine and picrobetol caused bronchodilatation. The antitussive and bronchodilatation effects of isoproterenol were abolished by propranolol. Each bronchoconstricting drug (i.e. morphine, codeine and HH-197) was administered concurrently with isoproterenol (10μg/kg, i.v., and non-antitussive activity), and the cough reflex was observed. Compared with the single administration of each drug, respiratory resistance was decreased and the anti-tussive effect was increased. These results indicate a strong correlation between bronchodilatation and increased antitussive activity.