Tazanolast inhibits ozone-induced airway hyperresponsiveness in guinea pigs.

We studied the inhibitory effect of tazanolast, a selective mast-cell-stabilizing drug, on ozone-induced airway hyperresponsiveness in guinea pigs. Airway responsiveness to methacholine peaked at 2 h after ozone exposure (2.0 ppm for 2 h) and the number of neutrophils in bronchoalveolar lavage (BAL) fluid continued to increase until 6 h. Tazanolast administered before ozone exposure at doses of 30, 100, or 300 mg/kg inhibited ozone-induced airway hyperresponsiveness in a dose-dependent manner. However, tazanolast administered after ozone exposure did not inhibit the airway hyperresponsiveness. Tazanolast did not significantly change the cell distribution of BAL cells at 2 h after the exposure. We conclude that tazanolast significantly inhibits ozone-induced airway hyperresponsiveness in guinea pigs. This result suggests that mast cells may play an important role in its development.