IMPLICATION OF OXYGEN RADICALS ON AIRWAY HYPERRESPONSIVENESS AFTER OVALBUMIN CHALLENGE IN GUINEA-PIGS

We elucidated the implication of oxygen radicals on airway hyperresponsiveness after ovalbumin (OA) challenge in guinea pigs. Ten days OA exposure increased airway responsiveness, i.e., a significant decrease in log [acetylcholine (Ach) PC200] (2.445 +/- 0.227) was observed compared with the control group (3.398 +/- 0.269). After OA exposure, the number of beta-adrenoceptors decreased by 38%, and adenylate cyclase activity decreased by 36% (isoproterenol stimulated) and 28% (basal). Significant increases in xanthine oxidase activities in lung tissue, bronchoalveolar lavage fluid (BALF), and serum were observed after the tenth OA exposure (49.1 +/- 11.7 mU/g tissue, 12.6 +/- 3.16 mU/ml, and 11.5 +/- 2.66 mU/ml, respectively) compared with those in the control group (7.35 +/- 6.48 mU/g tissue, 2.85 +/- 1.17 mU/ml, and 3.51 +/- 1.15 mU/ml, respectively). Administration of long-acting superoxide dismutase (SOD) (5,000 U/kg twice a day intraperitoneally) or gamma-glutamylcysteine ethyl ester (gamma-GCE) (10 mg/kg, twice a day, intraperitoneally), a prodrug of glutathione, maintained log [Ach PC200] (3.248 +/- 0.415 and 3.298 +/- 0.246, respectively) in spite of 10 days OA exposure. Decreases in the number of beta-adrenoceptors and adenylate cyclase activity were prevented by long-acting SOD or gamma-GCE. In contrast, long-acting SOD or gamma-GCE inhibited significantly, but not completely, the elevation of xanthine oxidase activities. These results support suggestions that oxygen radicals might be involved in the underlying mechanism of airway hyperresponsiveness after OA challenge in guinea pigs.