The American journal of physiology
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At ambient temperature (Ta) 20 and 10 degrees C, metabolic heat production and hypothalamic temperature (Thypo) were measured to determine the fever response in six rabbits injected with polyriboinosinic-polyribocytidylic acid (poly I:C; 5 mg/kg iv). Similar measurements were made in afebrile and febrile animals subjected to 3 h of body cooling, in which heat was extracted with a chronically implanted intravascular heat exchanger in a ramplike manner. ⋯ The net effect at the end of the cooling period was that Thypo decreased by 0.4 and 0.6 degree C more than in the afebrile cooling experiments at Ta 20 and 10 degrees C, respectively. The results indicate normal shivering responses during phase I of poly I:C-induced fever and depressed shivering in phase I, possibly because of a reduced thermosensitivity.