Journal of Applied Physiology, Vol 39, Issue 2 226-230, Copyright © 1975 by American Physiological Society
Circadian variations in the sweating mechanism
J. Timbal, J. Colin and C. Boutelier
Sweat rates and body temperatures of human subjects were measured at 0200,
1000, and 1800 h during a heat exposure of 90 min. The latent period of
sweating was not significantly altered in the evening but significantly
shortened during the night. Mean body temperature corresponding to the
onset of sweating was nearer to the basal body temperature during the
night, while during the day the difference between these two temperatures
became larger. This phenomenon seems related to the circadian cycle of
vasomotor adjustment, since during the night body conductance was higher
than during the day and corresponded to a state of a vasodilatation similar
to that observed at the onset of sweating. During the day, this situation
was reversed. During steady state, the following changes were observed:
sweating rate, night less than morning less than evening; skin
temperatures, night less than morning less than evening; and rectal
temperature increase, morning less than evening less than night. It is
hypothesized that these changes are due to either different metabolic rates
or an imbalance between heat gains and losses which preserve the circadian
rhythm of the body temperature, even under thermal loads.
