Factors responsible for the loss of respiratory burst capacity (stimulated extracellular O2-. release) of alveolar macrophages (AM) exposed to prolonged hyperoxia were assessed. Specific pathogen-free rats were exposed to 1 ATA O2 for 24-72 h, and lungs of survivors lavaged. Release of O2-. by cells after addition of concanavalin A, which stimulated AM but not polymorphonuclear leukocytes (PMN), or digitonin, which stimulated both cell types, was measured using cytochrome c reduction +/- superoxide dismutase. O2-. release by AM declined 47.2% (P less than 0.05) after 24 h of hyperoxia and 100% after 60 h. Percent PMN in the lavage was less than 3% at 0-36 h but increased to 16% at 48 h and to 44% at 72 h. Although addition of PMN to AM in vitro caused inhibition of AM O2-. release, the percent PMN required for inhibition was not reached in vivo until after a significant decline in AM O2-.-releasing capacity had already occurred. Cell-free lavage fluid from either control or hyperoxic rats did not affect AM O2-. release. AM in culture for 24 h in hyperoxia lost 76.7% (P less than 0.005) of O2-.-releasing capacity vs. cells incubated in 20% O2, although dye exclusion was unaffected. The results indicate that the major cause of loss of AM O2-. release by hyperoxia is a direct effect of O2 on the cells.
A B S T R A C T Bacterial infection may complicate pulmonary oxygen (02) toxicity, and animals exposed to high 02 concentrations show depressed in vivo pulmonary bacterial inactivation. Therefore, in vitro studies were undertaken to define the mechanism by which 02 alters pulmonary antibacterial activity. Normal and BCG pretreated rabbits were exposed to 100% 02 for 24, 48, and 72-h periods. Pulmonary alveolar macrophages (PAM) were obtained from the experimental animals and from nonoxygen exposed controls by bronchopulmonary lavage. 02 exposure did not alter cell yield or morphology. PAMs were suspended in 10% serum-buffer, and phagocytosis of ["C]Staphylococcus aureus 502A and ["C]Pseudomonas aeruginosa was measured. Comparison of the percent uptake of the "Clabeled S. aureus after a 60-min incubation period demonstrated that normal PAMs exposed to 02 for 48 h showed a statistically significant increase in phagocytosis when compared to their controls (43.5 vs. 29.2%). A similar, but smaller, increase was seen after 24-h 02 exposures. 48 and 72-h 02 exposures produced no significant changes in phagocytosis in PAMs from BCG-stimulated rabbits. Normal PAMs also showed an increased phagocytosis of Ps. aeruginosa after 48-h oxygen exposures. No impairment of in vitro bactericidal activity against either S. aureus 502A or Ps. aeruginosa could be demonstrated in PAMs from normal rabbits exposed to 02 for 48 h. These results indicate that the in vitro phagocytic and bactericidal capacity of the rabbit PAM is relatively resistant to the
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