Endotoxin protection of rats from pulmonary oxygen toxicity: lack of complement involvement.

Endotoxin (1 mg/kg, I.P.) greatly reduces lung damage and pleural edema in rats exposed to greater than 99% oxygen. Endotoxin also activates and depletes complement in vitro. Prior in vivo complement depletion has been shown to protect rats from lung edema in some experimental models. This study was designed to evaluate the possibility that endotoxin may protect rats from oxygen toxicity by activating and thereby depleting complement. We found no significant changes in complement hemolytic activity in serum from endotoxin pretreated rats breathing greater than 99% oxygen at sea level for 60 hours. We also found that complement depletion prior to oxygen exposure failed to protect rats from the lung damage of oxygen toxicity. These results indicate that the mechanism of endotoxin protection from pulmonary oxygen toxicity does not involve complement.