AJP - Lung Cellular and Molecular Physiology, Vol 272, Issue 6 1152-L1160, Copyright © 1997 by American Physiological Society
Pulmonary cell kinetics and morphometry after ozone exposure: day versus night and dose response in rats
H. Witschi, I. Espiritu and K. E. Pinkerton
Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis 95616, USA.
Male Sprague-Dawley rats were exposed to increasing concentrations of ozone
as follows: 0.12, 0.24, 0.36, 0.6, or 0.8 ppm. Controls were kept in
chambers ventilated with filtered air. One-half of the animals in ozone was
exposed for 12 h a day during daytime hours, and the other one-half of the
animals was exposed for 12 h during nighttime. Cumulative labeling indexes
were measured after 4 and 7 days in the terminal bronchioles, large
intrapulmonary airways, trachea, and nasal epithelia. The penetration of
the lesions from the bronchiole-alveolar junction into the alveolar zone
was measured with quantitative morphometry. After 4 days of exposure, the
extent of injury was dose dependent. Labeling indexes in the terminal
bronchioles were 15-20% higher in animals exposed during nighttime compared
with the animals exposed during daylight hours. On the other hand, depth of
penetration of ozone lesions into the centriacinar region was not
significantly different in animals exposed during the night compared with
animals exposed during daytime. Labeling indexes in the large airways,
trachea, or nasal cavity were not influenced by time of exposure. Between
days 4 and 7, the lesions in the terminal bronchioles progressed only to a
minimal degree (10%). It was concluded that the pattern of centriacinar
tissue remodeling 1) followed a gradient based on ozone concentration and
2) was essentially complete after only 4 days of ozone exposure. Although a
difference between daytime and nighttime exposure was observed, it was not
considered to be large enough to invalidate conclusions drawn from studies
in which animals are exposed to ozone during daylight hours.
