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Physiology Program, Harvard School of Public Health, Boston, Massachusetts 02115
During ozone
(O3) exposure, adult rats decrease their minute ventilation
(
E). To determine whether
such changes are also observed in immature animals, Sprague-Dawley
rats, aged 2, 4, 6, 8, or 12 wk, were exposed to O3 (2 ppm)
in nose-only-exposure plethysmographs. Baseline
E normalized for body weight decreased with age from 2.1 ± 0.1 ml · min
1 · g1
in 2-wk-old rats to 0.72 ± 0.03 ml · min1 · g1
in 12-wk-old rats, consistent with the higher metabolic rates of
younger animals. In adult (8- and 12-wk-old) rats, O3
caused 40-50% decreases in E that
occurred primarily as the result of a decrease in tidal volume. In
6-wk-old rats, O3-induced changes in
E were significantly less, and in 2- and 4-wk-old rats, no significant changes in
E were observed during O3
exposure. The increased baseline E and
the smaller decrements in E induced by
O3 in the immature rats imply that their delivered dose of O3 is much higher than in adult rats. To determine whether
these differences in O3 dose influence the extent of
injury, we measured bronchoalveolar lavage protein concentrations. The
magnitude of the changes in bronchoalveolar lavage induced by
O3 was significantly greater in 2- than in 8-wk-old rats
(267 ± 47 vs. 165 ± 22%, respectively, P < 0.05).
O3 exposure also caused a significant increase in
PGE2 in 2-wk-old but not in adult rats. The results
indicate that the ventilatory response to O3 is absent in
2-wk-old rats and that lack of this response, in conjunction with a
greater specific ventilation, leads to greater lung injury.
lung injury; prostaglandin E2; bronchoalveolar lavage; neutrophils; inflammation
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