[The role of thromboxane A2 in the development of airway responsiveness after platelet activating factor inhalation in dogs]

Abstract

To determine whether thromboxane A2 (TxA2) is involved in airway hyperresponsiveness after platelet activating factor (PAF) inhalation, we studied the effect of a specific TxA2 receptor antagonist, AA-2414 on the development of airway responsiveness induced by PAF inhalation in six dogs. Airway resistance and airway responsiveness to inhaled methacholine were determined by modified Astograph (7 Hz oscillation method). PAF inhalation (1000 micrograms/ml, ten minutes) caused a significant increase of airway resistance (p less than 0.01), and the increase of airway resistance was not inhibited by pretreated AA-2414. Airway responsiveness to inhaled methacholine increased significantly 3 hr after PAF inhalation (p less than 0.01). Pretreated AA-2414 inhibited the increase of airway responsiveness significantly (p less than 0.01), but the inhibition was partial. After PAF inhalation, total cell counts, neutrophil counts, eosinophil counts and the levels of TxB2 in bronchoalveolar lavage fluid increased significantly (p less than 0.05), and these increase were not affected by pretreated AA-2414. These results suggest that TxA2 is not involved in the bronchoconstriction induced by PAF inhalation, but TxA2 plays a partial role in the development of airway responsiveness after PAF inhalation in dogs.