Fentanyl-induced airway hyperreactivity in the guinea pig

The bronchopulmonary effects of fentanyl were studied in mechanically ventilated, paralyzed guinea pigs that had been anaesthetized with pentobarbitone sodium. Fentanyl did not alter the resting bronchial tone but enhanced the bronchoconstrictor effects of 5-hydroxytryptamine in a dose-related manner. The enhancement induced by 20 micrograms kg-1 fentanyl was suppressed by pretreatments with 0.5 mg kg-1 naloxone or 5 mg kg-1 propranolol, but did not change after 3 mg kg-1 atropine. The bronchoconstrictor responses to histamine were also enhanced by 20 micrograms kg-1 fentanyl. These results suggest that fentanyl-induced airway hyperreactivity is not mediated by an increase in vagal tone but is due to a reduction in the central sympathetic drive and/or in the levels of circulating catecholamines, which occurs through stimulation of opiate receptors.