EFFECT OF TOTAL-BODY CORE COOLING DURING POLY I-C-INDUCED FEVER IN RABBITS

At ambient temperature (T-a) 20 and 10 degrees C, metabolic heat produ ction and hypothalamic temperature (T-hypo) were measured to determine the fever response in six rabbits injected with polyriboinosinic-poly ribocytidylic acid (poly I:C; 5 mg/kg iv). Similar measurements were m ade 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 fever time course showed a b iphasic pattern. During cooling in the febrile experiments, T-hypo rem ained constant or even slightly increased during the time correspondin g to the first phase of fever but rapidly fell during the second phase because of a depressed shivering response. The net effect at the end of the cooling period was that T-hypo decreased by 0.4 and 0.6 degrees C more than in the afebrile cooling experiments at T-a 20 and 10 degr ees C, respectively. The results indicate normal shivering responses d uring phase I of poly I:C-induced fever and depressed shivering in pha se II, possibly because of a reduced thermosensitivity.