Tumor necrosis factor α (TNF) is released systematically during the early phase of endotoxin induced fever. To study the effects of this cytokine in guinea pigs, 2 μg TNF were intra-arterially injected as a bolus or slowly infused within 60 min. Both modes of administration induced a biphasic elevation of the animals' abdominal temperature lasting 6 h and stimulated the release of endogenous interleukin-6 (IL-6)-like activity. The second phase of the thermal response and the release of endogenous IL-6-like activity were significantly higher, when TNF was slowly infused into the animals' circulation, in spite of a transiently higher TNF-like activity after the bolus injection of TNF. Both TNF and IL-6 may therefore be regarded as candidates to trigger the febrile response in guinea pigs.
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http://deepblue.lib.umich.edu/bitstream/2027.42/42862/1/18_2005_Article_BF01956462.pdf