Diurnal changes in rectal and body surface temperatures of conscious, chair-restrained rhesus macaques

A system has been established for continuous recording of rectal and body surface temperatures in conscious, chair-restrained rhesus macaques. Diurnal changes in rectal temperature and body surface temperatures of head, back, abdomen, and inner thigh were recorded for 24 hours under conditions of intermittent or constant light. When lights were on for 8 hours (0800 to 1600 hours) and off for 16 hours, maximal rectal temperatures (37.6 +/- 0.3 C) were observed at 0900 hours, whereas minimal rectal temperatures (36.7 +/- 0.4 C) were demonstrated between 0200 and 0400 hours. Mean rectal temperatures varied 0.9 C during a 24-hour period. A trend of diurnal changes in body surface temperatures was also observed with low surface temperatures recorded between 0400 and 0800 hours. The surface temperatures (33.8 to 36.5 C) were markedly lower than rectal temperatures (36.7 to 37.6 C) under the same experimental conditions. When macaques were subjected to constant light, high rectal temperatures were recorded between 0900 and 1700 hours and low rectal temperatures were observed between 2400 and 0300 hours with a mean variation of 0.7 C (36.3 +/- 0.15 to 37.0 +/- 0.2). Diurnal body surface temperature changes during constant light were less pronounced than those of rectal temperatures. Furthermore, low surface temperatures of abdomen and inner thigh recorded between 0200 and 0800 hours were similar to those obtained with macaques exposed to the light-dark condition.