AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 5 1266-R1272, Copyright © 1995 by American Physiological Society
Poly I:C-induced fever elevates threshold for shivering but reduces thermosensitivity in rabbits
O. Toien and J. B. Mercer
Department of Arctic Biology, University of Tromso, Norway.
Shivering threshold and thermosensitivity were determined in six conscious
rabbits at ambient temperature (Ta) 20 and 10 degrees C before and at six
different times after saline injection (0.15 ml iv) and
polyriboinosinic-polyribocytidylic acid (poly I:C)-induced fever (5
micrograms/kg iv). Thermosensitivity was calculated by regression of
metabolic heat production (M) and hypothalamic temperature (Thypo) during
short periods (5-10 min) of square-wave cooling. Heat was extracted with a
chronically implanted intravascular heat exchanger. Shivering threshold was
calculated as the Thypo at which the thermosensitivity line crossed resting
M as measured in afebrile animals at Ta 20 degrees C. There were negligible
changes in shivering threshold and thermosensitivity in saline-injected
rabbits. In the febrile animals, shivering threshold generally followed the
shape of the biphasic fever response. At Ta 20 degrees C, shivering
threshold was higher than regulated Thypo during the initial rising phase
of fever and was lower during recovery. At Ta 10 degrees C the shivering
thresholds were always higher than regulated Thypo except during recovery.
Thermosensitivity was reduced by 30-41% during fever.
