POLY I-C-INDUCED FEVER ELEVATES THRESHOLD FOR SHIVERING BUT REDUCES THERMOSENSITIVITY IN RABBITS

Shivering threshold and thermosensitivity were determined in six consc ious rabbits at ambient temperature (T-a) 20 and 10 degrees C before a nd at six different times after saline injection (0.15 mi iv) and poly riboinosinic-polyribocytidylic acid (poly I:C)-induced fever (5 mu g/k g iv). Thermosensitivity was calculated by regression of metabolic hea t production (M) and hypothalamic temperature (T-hypo) during short pe riods (5-10 min) of square-wave cooling. Heat was extracted with a chr onically implanted intravascular heat exchanger. Shivering threshold w as calculated as the T-hypo at which the thermosensitivity line crosse d resting M as measured in afebrile animals at T-a 20 degrees C. There were negligible changes in shivering threshold and thermosensitivity in saline-injected rabbits. In the febrile animals, shivering threshol d generally followed the shape of the biphasic fever response. At T-a 20 degrees C, shivering threshold was higher than regulated T-hypo dur ing the initial rising phase of fever and was lower during recovery. A t T-a 10 degrees C the shivering thresholds were always higher than re gulated T-hypo except during recovery. Thermosensitivity was reduced b y 30-41% during fever.