Biphasic fever: what triggers the second temperature rise.
Romanovsky, A. A., and C. M. Blatteis.
Department of Physiology and Biophysics; University of Tennessee at
Memphis, Memphis, Tennessee 38163
APStracts 2:0076R, 1995.
Romanovsky, A. A., and C. M. Blatteis. Biphasic fever: what triggers
the second temperature rise? Am. J. Physiol. 000 (Regulatory
Integrative Comp. Physiol. 00): R000-R000, 1995. The mechanism of
initiation of the second body temperature (Tb) rise of the typically
biphasic lipopolysaccharide (LPS) fever is not known. This study was
undertaken to test the hypothesis that the second Tb rise during
fever may be initiated as a direct consequence of the elevated Tb of
the first febrile rise. Experiments were conducted in conscious
guinea pigs implanted with intraperitoneal thermodes, intravenous
(i.v.) catheters, and intrahypothalamic thermocouples.
Intraperitoneal cooling (IPC) was performed by perfusing water
(22[acute]iC) through the thermode under afebrile conditions, during
the first (0-40 min after pyrogen injection) or second (80-120) min
phase of the biphasic LPS (2 g/kg, i.v.) fever, or during a
monophasic LPS (0.5 g/kg, i.v.) fever. Throughout IPC, the rate of
heat withdrawal was maintained at 11.6 1.2 mW/g. No IPC was performed
in the corresponding controls. When started immediately after LPS
administration at the higher dose, IPC completely blocked the first
phase of the biphasic fever. This blockade was followed by a Tb rise,
which, although similar to the rise in the second phase, might also
alternatively be interpreted as the delayed occurrence of the first
phase, previously suppressed by IPC. But we excluded the later
possibility by showing the absence of an overshoot in Tb restoration
after IPC applied during the second phase of biphasic fever, during
monophasic fever, or under afebrile conditions. We conclude,
therefore, that the second Tb rise of biphasic LPS fever is not
induced by the elevated Tb of the first febrile phase. The cause of
the second peak of the characteristic, biphasic febrile response to
i.v. LPS remains speculative.
Received 6 July 1994; accepted in final form 28 February 1995.
APS Manuscript Number R360-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 April 1995.