Time course of permeability changes and PMN flux in rat trachea following O3 exposure

Changes in rat tracheal epithelial permeability and polymorphonuclear leukocyte (PMN) populations during a 24-hr time period following a 3-hr exposure to 0.8 ppm ozone (O3) were investigated. An increase in permeability to 99mTc-diethylene-triaminepentaacetate (DTPA) occurred immediately after the exposure, peaked at the 8-hr time point and decreased to control level by 24 hr. For correlation with tracheal permeability, tracheal cross sections were stained with naphthol AS-D chloroacetate and PMNs were scored by their location as well as staining characteristics (positive or negative). The total PMN population remained at the control value at the 0-, 4-, and 8-hr time points, and increased at 12 hr, followed by a rapid decline to below the control value for the remaining time points. There was a shift at the 8-hr time point in the population location, from the vasculature to the interstitium, which returned to control values at 12 hr. The percentage stained PMNs increased significantly at 16 hr while remaining at control values for all other time points. The data reveal that there is a significant increase in tracheal epithelial permeability immediately after the exposure, but the overall increase in the PMN population is preceded by a lag phase. A decrease in the vascular pool of PMNs concomitant with an increase in the interstitial pool of PMNs suggests their migration from blood to the interstitium after ozone exposure. These data indicate that while PMNs may play a role in permeability changes of tracheal epithelium, the initiation is most likely due to other factors.