Patterns of body temperature during feeding in rats under varying ambient temperatures

Relationships between feeding and body temperature of rats were investigated at three ambient temperatures during the whole light/dark cycle. Basal liver temperature was negatively correlated with ambient temperature. Only at 29°C liver temperature indicated activation of autonomic and locomotory thermoregulatory responses due to heat stress. At 21°C, liver temperature was always higher than skin temperature. Both showed a clear circadian rhythm with higher values during the dark phase. Meal-associated temperature patterns were superimposed on this circadian rhythm. Liver and skin temperatures showed a preprandial and prandial rise. Liver temperature reached an almost similar peak value just above 39°C at the end of a meal, irrespective of meal size and ambient temperatures of 13°C and 21°C. Liver temperature reached this peak about 2 min earlier and dropped sooner than skin temperature. These results indicate a threshold liver temperature at which feeding activity stops. The present study suggests that temperatures do not exceed this value by adaptive autonomic thermoregulatory responses shifting heat flow from core to skin and by stopping all locomotory activities including feeding, thereby avoiding deterioration of vital organs and physiological processes due to hyperthermia.