ENDOTOXIN TOLERANCE ALTERS THERMAL RESPONSE OF GUINEA-PIGS TO SYSTEMIC INFUSIONS OF TUMOR-NECROSIS-FACTOR-ALPHA

In guinea pigs, intra-arterial infusions of 5 mu g/kg tumor necrosis factor-alpha (TNF; specific activity 20,000 U/mu g; duration of infusion 45-50 min) evoked a biphasic elevation of abdominal temperature lasting similar to 6 h. One week after systemic infusion of TNF, the animals started to receive either five intramuscular injections of bacterial Lipopolysaccharide (LPS from Escherichia coli; 20 mu g/kg) or equivalent volumes of solvent (0.9% NaCl) in intervals of 3 days. Fever in response to repeated injections of LPS was progressively attenuated; the animals developed endotoxin tolerance. Repeated injections with solvent did not cause any measurable changes in abdominal temperature. Three days after the fifth injection of LPS or solvent, all animals again received an intra-arterial infusion of 5 mu g/kg TNF. In guinea pigs injected five times with solvent, the biphasic elevation of abdominal temperature could again be observed in response to systemic infusions of TNF. In endotoxin-tolerant animals, however, only the first peak of the biphasic thermal response lasting similar to 60 min could be monitored after infusions with TNF. The second phase of the thermal response to administration of TNF, which normally lasts >5 h, was abrogated almost completely. The significant suppression of the febrile response to TNF infusions did not seem to be caused by a more rapid elimination of TNF from the circulation of endotoxin-tolerant guinea pigs. Circulating levels of TNF, measured 60 and 180 min after the start of TNF infusions, were not different before and after development of endotoxin tolerance. In conclusion, the development of endotoxin tolerance in guinea pigs is accompanied by a reduced responsiveness to TNF administered exogenously.