Concentration-response curves for histamine in isolated tracheal preparations of guinea-pigs in the absence (O) and presence (◊) of Edici (10 mg/ml) (2A), and in the presence (▲) of promethazine at a concentration of 0.25 mg/ml (2B). Concentration of histamine are expressed as the log10 of the molar concentration. Each Point represents the mean values obtained using 6 rings. Each obtained from different animal. Brackets indicate SEM (n = 4-6).