Effect of ozone treatment on airway reactivity and epithelium-derived relaxing factor in guinea pigs

Ozone (O-3) is toxic to respiratory epithelium and causes airway inflammati on and hyperreactivity. To evaluate the role of the epithelium in the devel opment of hyperreactivity, we examined in guinea pigs the effects of inhale d O-3 (3 ppm for 1 h; 0-24 h after exposure) on 1) reactivity to inhaled me thacholine (MCh), 2) reactivity of the isolated, perfused trachea (IPT) to MCh, 3) epithelium-derived relaxing factor (EpDRF)-mediated relaxations of IPT induced by mucosal hyperosmolar solutions, 4) neurogenic contraction an d relaxation responses, 5) transepithelial potential difference, and 6) mic roscopic analysis of nitrotyrosine immunofluorescence, substance P fiber de nsity, and tracheal morphology. At 0 h, O-3 caused hyperreactivity to inhal ed MCh and mucosally but not serosally applied MCh in IPT (only in the pres ence of the epithelium) and a decrease in transepithelial potential differe nce. Inhibition of EpDRF-induced relaxation responses occurred at 2 h. All of these changes returned to control by 12 to 18 h. O-3 had no effect on ne urogenic responses. Nitrotyrosine immunofluorescence appeared in the trache a at 0 h in detached epithelial cell ghosts and in intrapulmonary airways b y 6 h. Substance P fiber density was elevated in smooth muscle at 0 and 18 h but not in epithelium or lamina propria of intrapulmonary and extrapulmon ary bronchi. Loss of cilia and mucosubstances in the mucosa occurred at 0 h ; the epithelium became markedly attenuated over 12 to 24 h. A reversible i ncrease in epithelial permeability and a decrease in EpDRF production may c ontribute to O-3-induced hyperreactivity to MCh.