THERMOGENIC RESPONSES TO BODY COOLING DURING FEVER INDUCED BY STAPHYLOCOCCUS-AUREUS CELL-WALLS IN RABBITS

Hypothalamic temperature (T-hypo) and metabolic heat production (M) we re measured in seven conscious rabbits injected intravenously with eit her saline or with Staphylococcus aureus, (8.10(7) cell walls.kg(-1)) while being subjected to a 3-h period of ramp-like total body cooling using a chronically implanted intravascular heat exchanger. In pyrogen -injected animals cooling started (1) at the time of injection or (2) 70 min after injection. in (1) the fall in T-hypo induced by heat extr action was similar (1.0 degrees C) in afebrile and febrile animals. In (2) there was a transient increase in T-hypo of about 0.5 degrees C a t a time corresponding to the start of fever resulting in a significan tly smaller fall in T-hypo at the end of the 3-h cooling period (0.5 d egrees C vs 0.9 degrees C, P < 0.05, n = 5). At this time in both (1) and (2) M was lower than theoretically expected from the increase in s hivering threshold during fever. However, most of this effect can be e xplained when available data showing a decrease in thermosensitivity d uring S. aureus-induced fever are taken into account. After cessation of cooling in both groups of febrile animals T-hypo rose to about 1 de grees C higher than the precooling level, which is comparable to the f ever level in a separate series of experiments with S. aureus injectio n without cooling (1.2 degrees C).