Ventilatory responses to ozone are reduced in immature rats

During ozone (O-3) exposure, adult rats decrease their minute ventilation ( VE). To determine whether such changes are also observed in immature animal s, Sprague-Dawley rats, aged 2, 4, 6, 8, or 12 wk, were exposed to O-3 (2 p pm) in nose-only-exposure plethysmographs. Baseline VE normalized for body weight decreased with age from 2.1 +/- 0.1 ml.min(-1).g(-1) in 2-wk-old rat s to 0.72 +/- 0.03 ml.min(-1).g(-1) in 12-wk-old rats, consistent with the higher metabolic rates of younger animals. In adult (8- and 12-wk-old) rats , O-3 caused 40-50% decreases in VE that occurred primarily as the result o f a decrease in tidal volume. In 6-wk-old rats, O-3-induced changes in VE w ere significantly less, and in 2- and 4-wk-old rats, no significant changes in VE were observed during O-3 exposure. The increased baseline VE and the smaller decrements in VE induced by O-3 in the immature rats imply that th eir delivered dose of O-3 is much higher than in adult rats. To determine w hether these differences in O-3 dose influence the extent of injury, we mea sured bronchoalveolar lavage protein concentrations. The magnitude of the c hanges in bronchoalveolar lavage induced by O-3 was significantly greater i n 2- than in 8-wk-old rats (267 +/- 47 vs. 165 +/- 22%, respectively, P < 0 .05). O-3 exposure also caused a significant increase in PGE(2) in a-wk-old but not in adult rats. The results indicate that the ventilatory response to O-3 is absent in a-wk-old rats and that lack of this response, in conjun ction with a greater specific ventilation, leads to greater lung injury.