Untersuchungen zur Rolle lokaler Zytokininduktion und deren nachgeschalteter Signale bei der Fieberreaktion des Meerschweinchens (Cavia aperea porcellus)

Abstract

The role of local cytokin formation and its consequent signalling during fever reaction in guinea pigs (cavia aperea porcellus)

In guinea pigs (Cavia aperea porcellus), fever was induced by injections of 100 µg/kg or 10 µg/kg lipopolysaccharide (LPS) into artificial subcutaneous chambers and analysed under the influence of the local anesthetic ropivacaine (ROPI), which was administered into the chamber at a dose of 10 mg/kg 30 min. prior to LPS. In response to injections of 100 µg/kg LPS into the subcutaneous chamber, fever was not modified by pretreatment with ROPI. High amounts of bioactive tumor necrosis factor a (TNF) and interleukin-6 (IL6) were measured in the lavage of the chambers after administration of LPS. Comparatively low concentrations of both cytokines (0.5 - 4%) of the concentrations in the lavage fluid were detected in blood plasma simultaneously. In response to injections of 10 µg/kg LPS into the subcutaneous chamber, fever was significantly reduced by pretreatment with ROPI to about 60 % of the febrile response of control animals. Levels of TNF and IL6 were lower in response to the reduced dose of LPS. TNF in plasma was even below the limit of detection. The suppression of fever by the local anesthetic was not observed when ROPI was subcutaneously injected into the contralateral site of the chamber position, so that a systemic effect of ROPI in the reduction of fever can be excluded. The results indicate a participation of afferent neural signals in the manifestation of fever. This effect becomes obvious only if the dose of the applied inflammatory stimulus (LPS) is not high enough to activate a systemic generalised inflammatory response. In the following experiments the roles of tumor necrosis factor a (TNFa), prostaglandins (PGs) and nitric oxide (NO) in this experimental fever model was investigated. A neutralizing TNF binding protein (TNFbp), or an inhibitor of NO-synthases (N-nitro-L-arginine-methylester, L-NAME), or an inhibitor of cyclooxygenases (diclofenac) was injected along with the high or low dose of LPS into the artificial subcutaneous chamber. In control groups both doses of LPS were administered into the chamber along with 0.9 % saline. The integrated fever responses to the high and low doses of LPS were not significantly attenuated by treatment with TNF bp in spite of a complete neutralization of bioactive TNF within the inflamed tissue area as determined by TNF measurements. Blockade of NO-formation by the treatment with L-NAME did not alter the febrile response to the high dose of LPS, but significantly attenuated fever induced by the low dose of LPS. Blockade of PG-formation by treatment with diclofenac not only completely abolished fever in response to both applied doses of LPS but even caused a slide hypothermic response. In conclusion, PGs seem to be essential components within the neural and humoral fever pathways from a site of localized tissue inflammation to the brain. A role of NO within these pathways is likely as well but less important. While circulating TNF significantly contributes to fever in response to systemic injections of LPS, the local formation of this cytokine within inflamed subcutaneous tissue seems not to provide a significant contribution within the fever pathways which are activated by localized administration of LPS into artificial subcutaneous chamber.