Circadian rhythms in body temperature of the pigtailed macaque (Macaca nemestrina) exposed to different ambient temperatures.

The body and leg skin temperatures of five pigtailed macaques (Macaca nemestrina) were measured at various ambient air temperatures ranging from 22 to 32°C over 24-h periods. The rhythm in core body temperature persisted in all ambient air temperatures, and the rhythm in leg skin temperature was suppressed at the higher and lower ambient temperatures. This suggests that at the upper and lower regions of the thermoneutral zone, either a rhythm in heat production or a heat loss rhythm other than leg skin temperature is regulating the core body temperature rhythm. It was also found that the mean colonic temperature increased linearly with an increase in ambient temperature and that a phase relationship existed between ambient temperature and colonic temperature. In addition, as the ambient temperature increased, additional sites along the distal portion of the leg were recruited for vasomotor heat loss.