Effect of C-fiber-mediated, ozone-induced rapid shallow breathing on airway epithelial injury in rats

We examined the relationship between C-fiber-mediated, ozone-induced rapid shallow breathing and airway epithelial cell injury at different airway sit es within the lower respiratory tract of conscious Wistar rats (n = 24). We combined an acute 8-h ozone inhalation with vagal perineural capsaicin tre atment, a selective C-fiber conduction block, and 5-bromo-2'-deolyuridine ( BrdU) labeling as an index of epithelial injury. Vehicle-treated rats that inhaled ozone developed a rapid shallow breathing pattern during ozone inha lation, whereas the capsaicin-treated rats that inhaled ozone showed no cha nges in respiratory frequency. In vehicle-treated, ozone-exposed rats that developed rapid shallow breathing, a progressive increase in BrdU-Iabeling density (no. of BrdU-Iabeled cells/ mm(2) airway) was observed starting at the bifurcation of the left main stem bronchi (central airway) and going do wn either a short or long airway path. In vehicle-treated, ozone-exposed ra ts, terminal bronchioles supplied by short and long airway paths had a simi lar degree of BrdU-Iabeling density that was significantly (P < 0.05) great er than the BrdU-labeling density of the proximal airways that supply them. In contrast, the attenuation of rapid shallow breathing produced by capsai cin treatment resulted in a significantly reduced BrdU-Iabeling density in the terminal bronchioles supplied by short airway paths compared with the t erminal bronchioles supplied by long airway paths. Our data indicate that o zone-induced rapid shallow breathing protects large conducting airways whil e producing a more even distribution of injury to terminal bronchioles.