Fever in rats after intravenousE. coli endotoxin administration

Summary In conscious unrestrained rats, at an ambient temperature of 22°C, oesophageal temperature was measured and temperature effect of single and repeated intravenous injection ofE. coli endotoxin was examined. The first injection of endotoxin in a dose of 10.0 g/rat did not change the rat body temperature. The second injection of this dose in the same animals repeated after 48 h produced fever. With following injections the fevers observed were less pronounced. The absence of fever after a single injection of endotoxin was accompanied by the rapid loss of pyretic activity of the rat plasma samples (bioassayed in rabbits). When fever was observed (48 h interval between endotoxin injections) the pyretic activity of the rat plasma remained unchanged for 90 min following endotoxin injection. It was concluded that after a single injection endotoxin is rapidly detoxified in the rat circulation while this process does not take place after the second endotoxin injection (48 h interval). The process of endotoxin detoxification can be depressed by the pretreatment with nitrogen mustard. Analysis of changes of skin temperature following endotoxin injections and the influence of aspirin on endotoxin-induced fever suggest that the fever observed was of central origin.