OXYGEN-TOXICITY - PROTECTION OF THE LUNG BY BACTERIAL LIPOPOLYSACCHARIDE (ENDOTOXIN)

Adult rats were exposed to > 95% O2 for a 72-hr period and treated with small dosages of endotoxin (250 μg/kg/day, ∼ 1 100th LD50) during the exposure or with a single dose of endotoxin (500 μg/kg) administered just prior to the hyperoxic exposure. Endotoxin treatment increased the survival rate in hyperoxia from 12 44 (27%) for untreated rats to 38 40 (95%) for the treated animals (p < 0.05). In addition, the endotoxin-treated animals had significantly decreased O2-induced pulmonary edema and pleural fluid accumulation compared to the untreated rats (p < 0.05). Histological examination by light microscopy demonstrated marked lung damage in the untreated. hyperoxia-exposed animal lungs (perivascular, interstitial, and alveolar edema and lung hemorrhage) but only minimal changes in the lungs of the endotoxin-treated group of animals exposed to hyperoxia. Transmission electron microscopy showed a protective action of endotoxin treatment on the pulmonary capillary endothelium, compatible with the decreased exudative changes (edema) observed in the O2-exposed endotoxin-treated lungs. Indomethacin and methylprednisolone pretreatment failed to alter the protective action of endotoxin versus pulmonary O2 toxicity. © 1979.