Acute NO2 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.