Acute IMO2 Effects on Penetration and Transport of Horseradish Peroxidase in Hamster Respiratory Epithelium

Abstract

Male Golden Syrian hamsters were exposed to 28 ppm NO₂ for 48 h. Intratracheal instillations of 25 mg horseradish peroxidase (HRP) in 0.2 ml saline followed exposure. After 10-to 30-min incubation periods, lungs were perfusion-fixed and excised, and bronchi, bronchioles, and alveolar tissues were isolated. A second group of NO₂-exposed hamsters was allowed a 48-h recovery period prior to HRP instillations, and a third group served as air controls. Analysis by transmission electron microscopy of airways showed penetration by tracer material of 75% of bronchiolar tight junctions (TJ) examined after 48-h exposures. Only 15% of bronchial TJ were penetrated. No bronchial TJ were compromised after the recovery period, but 20% of bronchiolar TJ remained permeable. The TJ from bronchi and bronchioles of control animals showed no penetration of HRP; HRP penetration of interalveolar TJ was not seen in control animals or in “recovery” animals, but it was observed in 30% of the TJ after 48-h exposures. All penetrated junctions were between adjacent type I pneumocytes. Many pinocytotic vesicles in alveolar type I pneumocytes containing HRP could be seen 10 and 30 min after instillation in animals exposed to NO₂. Control animals showed a similar pattern; however, fewer vesicles were present. The number of pinocytotic vesicles was analyzed statistically for each exposure and control group. The data indicated a 500% increase in vesicle number after 48 h of NO₂ exposure. After 48 h of recovery the number of vesicles was 300% greater than that present in the control animals. These data were not altered by peroxidase stain. Vesicle size was found to be the same (80 nm in diameter) in NO₂-exposed and control specimens. Our results suggest differing effects of NO₂ on bronchial, bronchiolar, and alveolar epithelium. This observation confirms previous studies that the TJ of bronchiolar epithelium are most sensitive to NO₂-induced injury. Further, the data indicated that NO₂ injury increases endocytic activity of the alveolar type I cells.