EFFECT OF AN INHALED CORTICOSTEROID ON AIRWAY EOSINOPHILS AND ALLERGEN-INDUCED AIRWAY HYPERRESPONSIVENESS IN DOGS

The presence of airway eosinophils before allergen inhalation may cont ribute to the development of allergen-induced airway responses. We exa mined whether a reduction in airway eosinophil numbers before allergen inhalation as a result of inhalation of the corticosteroid budesonide would prevent allergen-induced airway hyperresponsiveness in seven do gs. Acetylcholine airway responsiveness was measured before and 24 h a fter inhalation of Ascaris suum allergen (10(-6)-10(-2) wt/vol) or its diluent on 4 test days separated by greater than or equal to 4 wk. Do gs were pretreated for 7 days before and on the morning of each test d ay with inhaled budesonide (2.69 mg/day) or a placebo (lactose). Airwa y eosinophil numbers were assessed by bronchoalveolar lavage. Inhaled budesonide significantly reduced the number of airway eosinophils befo re allergen inhalation from 3.6 +/- 2.38 X 10(4) (SE) cells/ml after i nhaled lactose to 0.3 +/- 0.21 X 10(4) cells/ml after inhaled budesoni de (P = 0.028). The decrease in eosinophil number was associated with a significant reduction in allergen-induced airway hyperresponsiveness (P = 0.005). These results support the hypothesis that the number of eosinophils in the airways before allergen inhalation is an important determinant in the development of allergen-induced airway hyperrespons iveness in dogs.