Abstract
Glaser and Shepherd (1961, 1963) suggested that man could be acclimatized simultaneously to both heat and cold. In this study, effects of heat- and cold-acclimation on thermoregulatory responses were examined in rats. Male Wistar rats aged 10, 22 and 53 wk were used. The rats were housed separately for 28 days under controlled conditions of ambient temperature (Ta) of 32°C from 9:00 to 21:00 and Ta of 5°C from 21:00 to 9:00, and 12 h light/dark cycle. Control rats were housed under constant Ta of 23°C for 28 days. After the acclimation period, thermoregulatory responses to the acute thermal stress were examined. Core temperature (Tc) and heart rate (HR) were continuously measured by using a telemetry system throughout the experiment. Rats aged 10 wk could regulate their Tcs within a narrow range during the acute thermal stress regardless of acclimated or not. Acclimated rats aged 10 wk showed a lower Tc and HR levels than those of unacclimated rats under warm Ta range (20 to 30°C). Tcs and HRs of acclimated rats aged 22 and 53 wk showed a lower levels than those of unacclimated rats of the same age under cold Ta range (0 to 10°C), but remarkable effect was not observed under warm Ta range. In summary, cold-acclimated effects were apparently observed in Tc and HR responses rather than warm-acclimated effects in warm- and cold-acclimated rats aged 22 and 53 wk. [J Physiol Sci. 2007;57 Suppl:S88]
