Differential Lung Responses to Early Life Ozone Exposure in Male and Female Rat Offspring
Authors: Dye Janice , Stewart Erica , Schladweiler Mette , Copeland Lisa , Kodavanti Urmila , Miller Colette 
Published: April 2020

The role that early life events (intrauterine growth restriction) and environmental exposures (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) on 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.

Immediately post‐exposure (0h), baseline (BL) spontaneous ventilation [i.e., breathing frequency (f), tidal volume (TV), and PenH, a unitless parameter suggestive of bronchoconstriction] 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. At 4h, the left lung lobe was fixed (at 20 cm H2O) for volume displacement and histology. Right lobes were lavaged to assessed lung injury and inflammation. Two‐way ANOVAs were used to assess male (M) and female (F) responses separately; O3‐exposed groups were compared to Air‐exposed dams + postnatal (PN)‐Airx3)].

By week 7, in males, dam O3‐exposure resulted in 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. By the 3rd PN exposure, both M & F O3‐exposed rats continued to exhibit some degree of dyspnea at 0h, with corresponding 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. CO2 challenge increased breathing frequency in all rats, and F rats were more responsive in terms of enhanced TV increases (A+Ax3 and O3+Ax3 offspring increased 56 and 68%, respectively). M A+Ax3 and O3+Ax3‐exposed rats increased 45%. 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 increased 24%. Based on 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. Histopathologic changes are currently being analyzed.

In summary, female offspring, especially O3+O3x3 rats appear to have differences in lung function growth and acute O3 responses. The 6‐min 6%‐CO2 protocol was well tolerated and increased TV to approximately 50% of a maximal breath (FEV1). This approach may provide a sensitive, yet non‐invasive method to document differential lung growth trajectories in rodent models of early life stressors. (Abstract does not reflect USEPA policy).

Support or Funding Information

EPA funding; A‐E and SHC programs