Effect of fentanyl on the level of histamine in BALF. BALF was obtained by injecting 2 ml of ice-cold physiological saline (1 ml, twice) via a tracheal cannula 30 min after i.v. injection of fentanyl (5 μg/kg). Each column represents the mean with S.E.M (n = 10). * P < 0.05 vs. vehicle (saline)-treated group.