ENDOTOXIN PROTECTION AGAINST OXYGEN-INDUCED ACUTE AND CHRONIC LUNG INJURY

Small dosages of endotoxin (100-500 μg/kg) provide significant protection against the acute manifestations of pulmonary O2 toxicity and lethality. Ninety-seven percent of endotoxin-treated adult rats survived a 72-hr exposure to ≥95% O2 with minimal lung changes, compared to 32% of control animals (P < 0.01). Exposure to ≥95% O2 for 7 days resulted in a 20% survival rate in untreated control rats vs. 98% survival in endotoxin-treated rats (P < 0.01). Histological evaluation of lung from survivors revealed substantially less collagen and reticular fiber deposition in the endotoxin-treated animal lungs. Endotoxin treatment was associated with increased activity of the protectant antioxidant enzyme systems of the lung in an apparent dose-response manner. Endotoxin's protective activity against O2 toxicity does not appear to depend on an initial toxic insult to the lung like with α-naphthylthiourea, oleic acid, or alloxan treatment. The data support a protective role for endotoxin against the acute and the more chronic manifestations of O2-induced pulmonary injury.