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 sites within the lower respiratory tract of conscious Wistar rats (n = 24). We combined an acute 8-h ozone inhalation with vagal perineural capsaicin treatment, a selective C-fiber conduction block, and 5-bromo-2'-deoxyuridine (BrdU) labeling as an index of epithelial injury. Vehicle-treated rats that inhaled ozone developed a rapid shallow breathing pattern during ozone inhalation, whereas the capsaicin-treated rats that inhaled ozone showed no changes in respiratory frequency. In vehicle-treated, ozone-exposed rats that developed rapid shallow breathing, a progressive increase in BrdU-labeling density (no. of BrdU-labeled cells/mm(2) airway) was observed starting at the bifurcation of the left main stem bronchi (central airway) and going down either a short or long airway path. In vehicle-treated, ozone-exposed rats, terminal bronchioles supplied by short and long airway paths had a similar degree of BrdU-labeling density that was significantly (P < 0.05) greater than the BrdU-labeling density of the proximal airways that supply them. In contrast, the attenuation of rapid shallow breathing produced by capsaicin treatment resulted in a significantly reduced BrdU-labeling density in the terminal bronchioles supplied by short airway paths compared with the terminal bronchioles supplied by long airway paths. Our data indicate that ozone-induced rapid shallow breathing protects large conducting airways while producing a more even distribution of injury to terminal bronchioles.
Schelegle
E S
ES
Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, One Shields Road, Davis, CA 95616, USA. esschelegle@ucdavis.edu
Alfaro
M F
MF
Putney
L
L
Stovall
M
M
Tyler
N
N
Hyde
D M
DM
D000818:Animals; D000963:Antimetabolites; D001273:Atmosphere Exposure Chambers; D001973:Bromodeoxyuridine; D002452:Cell Count; D002455:Cell Division / Q000502:physiology; D004847:Epithelial Cells / Q000473:pathology; D004848:Epithelium / Q000473:pathology; D009412:Nerve Fibers / Q000502:physiology*; D010083:Oxidants, Photochemical / Q000633:toxicity*; D010126:Ozone / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D015656:Respiratory Mechanics / Q000187:drug effects*
D000963:Antimetabolites; D010083:Oxidants, Photochemical; D010126:Ozone; D001973:Bromodeoxyuridine