NEONATAL CAPSAICIN TREATMENT INCREASES THE SEVERITY OF OZONE-INDUCED LUNG INJURY

To test the hypothesis that lung sensory C fibers protect the small di stal airways and alveoli from oxidant injury, we compared the effects of inhalation of ozone (1 ppm) or filtered air for 8 h on lung injury and lung inflammation in four groups of rats: (1) normal rats exposed to filtered air; (2) normal rats exposed to ozone; (3) rats treated as neonates with capsaicin (50 mg/kg, intraperitoneally) and subsequentl y exposed to filtered air; and (4) rats treated as neonates with capsa icin and subsequently exposed to ozone. All rats were allowed to recov er in filtered air for 0, 4, 16, and 40 h before necropsy. Rats expose d to filtered air (Groups 1 and 3) showed normal airway and parenchyma structure. Normal untreated rats exposed to ozone showed a random dis tribution of mild, interstitial inflammatory changes and epithelial ne crosis of bronchi and bronchiolar epithelium. However, rats treated wi th capsaicin and subsequently exposed to ozone demonstrated severe acu te interstitial inflammation and epithelial coagulate necrosis in all airways, especially in small, peripheral airways and parenchyma; all o f these changes were statistically significant. These findings support our hypothesis that lung sensory C fibers protect the distal airways from oxidant injury during acute ozone inhalation.