REVERSAL OF PERSISTENT POSTBRONCHIOLITIS AIRWAY ABNORMALITIES WITH DEXAMETHASONE IN RATS

Viral bronchiolitis is a common disease that may result in persistent airway abnormalities. Previous studies of neonatal bronchiolitis in ra ts revealed chronic sequelae, including airway obstruction, airway hyp erresponsiveness, increased production of airway eicosanoids, and incr eased numbers of bronchiolar mast cells. To address the hypothesis tha t postbronchiolitis airway obstruction is caused in part by reversible processes, we tested whether obstruction could be reversed by a brief course of high-dose corticosteroids. Neonatal Brown Norway rats (5 da ys of age) were inoculated with parainfluenza type 1 virus or sterile vehicle. At 8 wk of age, rats were treated with dexamethasone (1.4 mg. kg(-1).day(-1) sc) or saline for 3 days and were evaluated for lung me chanics, gas exchange, and lung inflammatory cells 1 day after the las t injection. Dexamethasone normalized the chronic virus-induced airway obstruction and reduced the numbers of bronchiolar mast cells and oth er inflammatory cells. Resistance and dynamic compliance correlated si gnificantly with bronchiolar mast cells but not with other airway infl ammatory cell infiltrates. We conclude that the airway abnormalities t hat persist in rats after recovery from neonatal bronchiolitis are ass ociated with increased numbers of bronchiolar mast cells and are large ly due to corticosteroid-sensitive mechanisms.