AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 4 836-R841, Copyright © 1990 by American Physiological Society
Circadian variation of thermoregulatory responses during exercise in rats
H. Tanaka, M. Yanase, K. Kanosue and T. Nakayama
Department of Physiology, Osaka University Medical School, Japan.
Rats exercised on a treadmill at daytime lows and nighttime highs of
circadian change in body temperature at two different work intensities [40
and 60% of maximal oxygen uptake (VO2max)] with the ambient temperature
(Ta) at 24 degrees C. Immediately before exercise at 60% VO2max, rectal
temperature (Tre) was 0.7 degrees C higher at night than during the day.
During the exercise, Tre rose more during the day than at night, and Tre at
the end of exercise was the same in the day as at night. Threshold Tre for
tail vasodilation did not differ between day and night. Similar tendencies
of Tre change and tail vasomotor response were observed at a work intensity
of 40% VO2max, except that the rise in Tre was smaller than at the higher
work intensity. On the other hand, threshold Tre for tail vasodilation
spontaneously occurring in resting rats in a warm environment (Ta of 28
degrees C) was 0.7 degrees C higher at night than during the day. In
conclusion, exercise in rats attenuates the differences in deep body
temperature and threshold Tre for tail vasodilation seen between day and
night.
