Peripheral effects of Morphine and Codeine on the cough reflex.

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Abstract
Peripheral effects of morphine and codenine on the cough reflex were investigated using an in situ dog upper trachea perfusion preparation which allows for a direct drug administration to the local site around the tracheal mucosa, this site being electrically stimulated to induce coughing. An i.a. [intraarterial] administration of procaine or lidocaine into the tracheal vascular bed inhibited both cough response and tracheal constriction accompanied by coughing. Benzonatate inhibited the tracheal constriction without influencing the cough response. The in situ upper trachea perfusion preparation is useful for evaluating effects of drugs on the cough receptor level. Morphine, 0.1 mg, and codeine, 1.0 mg, injected i.a. into the tracheal artery, produced no tracheal constriction. Such administrations had no influence on the cough response elicited by mucosal stimulation, whereas the tracheal constriction accompanied by cough reflex was inhibited by both drugs. Both drugs inhibited the bronchoconstriction induced by electrical stimulation of the vagus nerve. Both morphine and codeine inhibit the tracheal constriction accompanied by cough reflex without producing a tracheal constriction, in addition to their central antitussive action.