Differential Lung Responses to Early Life Ozone Exposure in Male and Female Rat Offspring
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Differential Lung Responses to Early Life Ozone Exposure in Male and Female Rat Offspring. JA Dye1, EJ Stewart2, MC Schladweiler1, L Copeland1, UP Kodavanti1, and CN Miller2 1U.S. Environmental Protection Agency, Research Triangle Park, NC and 2ORISE, Oak Ridge, TN Background: The essential role that early life events (i.e., intrauterine growth restriction) and environmental exposures (i.e., air pollution) play in development of childhood asthma are only partly understood. We previously showed that exposure of Long-Evans rats to the oxidant air pollutant ozone (O3) during implantation [gestational days (GD) 5 and 6; 0.8 ppm x 4h] resulted in growth restriction at GD21. The aim of this study was to determine whether gestational ¿ repeated peri-adolescent O3-exposure of offspring (0.4–0.8 ppm x 4h; once/week at 5, 6, and 7 weeks-of-age) would alter lung growth or acute ventilatory response to O3 exposure. Methods: Immediately post-exposure, baseline (BL) spontaneous ventilation [i.e., breathing frequency (f), tidal volume (TV), minute volume (MV), and PenH, a unitless parameter suggestive of bronchoconstriction] parameters were obtained using whole body plethysmography (WBP) with EMKA iox 2 software (SCIREQ, Montreal, Canada) followed by a 6-min 6%-CO2 challenge to enhance tidal breathing. Rats were necropsied 4h later. The left lung lobe was fixed (at 20 cm H2O) for volume displacement and pathological assessment. Right lobes were lavaged to assessed lung injury and inflammation. Two-way ANOVA with Dunnett’s post hoc correction were used to assess male (M) and female (F) responses separately; all O3-exposed groups were compared to controls [air-exposed dams + postnatal (PN)-Airx3)] of the corresponding sex. Results: By week 7, in males, dam O3-exposure was associated with augmented body “height” (skull base-to-tail head); but not body weight, or weight adjusted by height (gm/cm). In females, PN-O3x3 exposure was associated with reduced weight/height (gm/cm). By the 3rd PN O3 exposure, both M & F ozone-exposed rats continued to exhibit some degree of dyspnea at 0h, with corresponding significant increases in BL Penh (F: 5.2-5.6 fold, M: 3.9-4.8 fold). Significant reduction in BL TVcorr (corrected for “height”) was apparent only in F O3+O3x3 rats. During CO2 challenge, breathing frequency increased in all rats, and F rats were more responsive in terms of CO2-enhanced TV increases (A-Ax3 and O3-Ax3 offspring showed 56 and 68% increases, respectively). M A-Ax3 and O3-Ax3-exposed rats had 45% increases. By contrast, O3-exposed F A-O3x3 and O3-O3x3 rats only had 25 and 40% increases, respectively; while M A+O3x3 and O3+ O3x3 rats had 24% increases. Based on CO2-enhanced TVcorr, values, both M and F O3-exposed offspring developed a “classic” short-and-shallow respiratory pattern acutely following exposure. In F but not M, offspring, CO2-enhanced TV was inversely correlated with PenH. WBP parameters returned to BL within 2 -4 minutes of CO2 discontinuation. At necropsy, dam O3-exposure was associated with lower lung (fixed) volumes in females. For both sexes, lung injury (increased protein leakage) and inflammation (neutrophils and cytokines in lavage fluid) were increased chiefly by PN-O3 exposure. Protein leakage increased proportionately with PenH increases. Histopathologic changes are currently being analyzed. Conclusions. Female offspring, especially the O3-O3x3 group appear to have differences in lung growth parameters and acute O3 responses. This 6-min 6%-CO2 protocol was well tolerated and increased breathing to approximately 50% of the fixed lung volume. Hence, it may provide a sensitive, yet non-invasive method to document differential lung growth trajectories in offspring experiencing early life stressors. (This abstract does not reflect USEPA policy).