The present study was designed to assess the effects of repeated subac
ute ozone (O-3) exposure on pulmonary inflammation and ventilation in
two inbred strains of mice differentially susceptible to a single O-3
exposure. Susceptible C57BL/6J (B6) and resistant C3H/HeJ (C3) mice we
re exposed to 0.3 ppm O-3 for 48 and 72 h and after 14 days recovery,
both strains were reexposed. Airway inflammation and lung injury were
assessed by counting inflammatory cells and measuring total protein co
ntent and lactate dehydrogenase (LDH) activity in bronchoalveolar lava
ge (BAL) returns. Minute ventilation [V-E, the product of breathing fr
equency (f), and tidal volume (V-T)] was measured prior to and immedia
tely following each exposure. After the initial exposure, B6 mice deve
loped greater O-3-induced increases in total protein, inflammatory cel
l influx, and LDH activity compared to C3 mice. In normal air, V-E, wa
s also significantly elevated in B6, but not C3, mice after O-3. The h
ypercapnic f of B6 and hypercapnic V-T of C3 mice were significantly a
ltered after O-3 exposure. Reexposure to O-3 caused a smaller increase
in the numbers of macrophages, lymphocytes, epithelial cells, and BAL
protein in both strains, and no changes in LDH activity. However, the
number of polymorphonuclear leukocytes significantly increased in B6
and C3 mice as compared to the initial O-3 exposure. In both strains,
the ventilatory responses to normal air or hypercapnia were largely re
producible after O-3 reexposure. Results indicated that differential s
usceptibility to O-3-induced inflammation was maintained in B6 and C3
mice with O-3 reexposure although the magnitude of the difference was
reduced. Results also suggest that the ventilatory responses to O-3 in
B6 and C3 mice were reproducible with reexposure, and that airway inf
lammation and ventilation were not codependent.