AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 4 781-R785, Copyright © 1993 by American Physiological Society
Circadian rhythms of thermoregulation in the squirrel monkey (Saimiri sciureus)
E. L. Robinson, V. H. Demaria-Pesce and C. A. Fuller
Section of Animal Physiology, University of California, Davis 95616-8519.
Phase or amplitude differences between rhythms in heat production (HP) and
heat loss (HL) have been suggested to account for the circadian rhythm in
body temperature (Tb). To describe the relationships among these rhythms in
a primate, five unrestrained squirrel monkeys (1.0-1.3 kg) were studied
using combined direct and indirect calorimetry, with telemetry of Tb and
activity, in a 24-h light-dark cycle (LD 12:12) at 25 +/- 0.5 degrees C.
Dry (D; sensible) HL, evaporative (E) HL, HP (oxygen consumption and CO2
production), Tb, and activity were measured at 10-min intervals for a week.
Tb, activity, HP, and HL displayed daily rhythms, peaking during the light
period. Although the timing of peaks was not significantly different, the
diurnal increase in Tb was seen to result from a delayed increase in DHL,
and possibly, EHL, relative to increased HP. The nocturnal decrease in Tb
was due to different time courses of decrease in HP and HL, with no clear
lag in HL. The rhythm in Tb therefore resulted from both phase and time
course differences in HP and HL rhythms.
