AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 4 842-R847, Copyright © 1990 by American Physiological Society
Effects of pyrogen administration on temperature regulation in exercising rats
H. Tanaka, K. Kanosue, M. Yanase and T. Nakayama
Department of Physiology, Osaka University Medical School, Japan.
To study the mechanism of rise in body temperature during exercise,
endogenous pyrogen was administered to exercising rats. At rest and at a
neutral ambient temperature (Ta) of 24 degrees C, intravenous injection of
recombinant human interleukin 1 (IL-1, 40 micrograms/kg) produced a 0.5
degree C rise in rectal temperature (Tre) from 37.4 degrees C. At Ta of 34
degrees C, at which Tre was 38.6 degrees C, Tre rise in response to IL-1
was only 0.2 degree C greater than when saline was used. In the first
series of exercise experiments, rats ran on a treadmill after IL-1 or
saline injection at two different work intensities (estimated at 40 and 60%
of maximal oxygen uptake) at 24 degrees C Ta. At either work intensity, the
magnitude of Tre rise after IL-1 injection was approximately 0.5 degree C
higher than after saline injection. Threshold Tre for tail vasodilation
increased when IL-1 was injected. The difference in the threshold Tre
between the IL-1 and saline conditions was 0.5 degree C at either work
intensity. Evaporative heat loss was also suppressed and metabolic heat
production facilitated when IL-1 was injected. In a second series of
experiments, IL-1 was injected after Tre reached a steady state (38.5
degrees C) during exercise. After IL-1 injection Tre increased another 0.5
degrees C, but after saline injection Tre did not change. These results
suggest that body temperature rise during exercise is not induced merely by
an insufficient capability of dissipating heat and that the
thermoregulatory set point is reset during exercise.
