Effect of oxygen and endotoxin on lactate dehydrogenase release, 5-hydroxytryptamine uptake, and antioxidant enzyme activities in endothelial cells

We compared the effects of 95% O2 (hyperoxia) alone, endotoxin (20 ng/ml) alone, and 95% O2 plus endotoxin on the release of lactate dehydrogenase (LDH), uptake of 5-hydroxytryptamine (5-HT), and antioxidant enzyme activities in porcine pulmonary arterial and aortic endothelial cells in monolayer culture. Hyperoxia increased LDH release and decreased 5-HT in both endothelial cell types. Hyperoxia also caused a decrease in catalase (CAT) activity and an increase in total superoxide dismutase (SOD) and glutathione reductase (GSH-Red) activities in both cell types. Endotoxin alone had no effect on LDH release, 5-HT uptake, or antioxidant enzyme activities. However, endotoxin prevented the hyperoxic increase in LDH release and the hyperoxic decrease in 5-HT uptake. Endotoxin plus 95% O2 had no consistent effect on the antioxidant enzyme profile in pulmonary artery or aortic endothelial cells. These results indicate that (1) hyperoxia injures both pulmonary artery and aortic endothelial cells in culture and causes changes in the antioxidant enzyme profile that are similar in the two cell types; (2) hyperoxia-induced decreases in CAT activity and increases in SOD activity may be responsible for increased sensitivity of endothelial cells to O2 toxicity; and (3) endotoxin protects against hyperoxic injury to endothelial cells in vitro, but increases in antioxidant enzyme activities are not the mechanism for this protection.