Endotoxin treatment protects vitamin E-deficient rats from pulmonary O2 toxicity

Endotoxin treatment in normal rats has a marked protective effect against O2 toxicity (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 577-581, 1979 and 51: 577-583, 1981), and endotoxin's protective action is associated with stimulation of the lung's enzymatic antioxidant defense system (superoxide dismutase, catalase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase). Vitamin E-deficient animals are especially sensitive to hyperoxidant stresses, including pulmonary O2 toxicity. In these studies we tested whether endotoxin could reverse the increased susceptibility of vitamin E-deficient rats to hyperoxic challenge. We found that untreated vitamin E-deficient rats do succumb more readily to O2 toxicity [0/11 alive at 72 h in greater than 95% O2, lethal time for 50% of the animals (LT50) = 50 h] than rats fed a regular diet (4/14 alive, LT50 = 69 h). In contrast, 15 of 16 vitamin E-deficient rats treated with endotoxin survived the same O2 exposures (P less than 0.001) and showed significantly reduced pulmonary edema compared with the other groups. The endotoxin-treated vitamin E-deficient group was also the only one to demonstrate significant elevations of all the antioxidant enzymes during O2 exposure, suggesting that the antioxidant enzyme defenses of the lung have a more primary and important role in prevention of O2-induced lung injury than the lipid-associated antioxidant, vitamin E.