EFFECT OF PHYSICAL RESTRAINT ON THE LIMITS OF THERMOREGULATION IN TELEMETERED RATS

Abstract

To understand how ambient temperature (Ta) affects the thermoregulatory response to restraint, core temperature (Tc) and heart rate (HR) were monitored by telemetry in rats subjected to one hour of physical restraint while Ta was maintained at 14 to 30 °C in 2 °C increments. Tc of unrestrained rats was unaffected by Ta. During restraint, Tc was elevated at all Ta's with exception to 14°C where the rats became mildly hypothermic. There was an inverse relationship between Ta and HR in both unrestrained and restrained rats; however, HR was significantly elevated in restrained rats at all Ta's except 22 and 24 °C. Heat loss from the tail, estimated from Tc and tail skin temperature, was markedly reduced at all but the highest Ta's in restrained rats. The data suggest that the Ta limits of normothermia (LIN) are narrowed in the restrained rat. That is, between 16 and 20 °C, the rat maintains a relatively stable Tc that is slightly elevated above that of the unrestrained rat. Overall, the ideal Ta for restrained rats appears to be 20 and no higher than 22°C for the thermoregulatory system to maintain a regulated Tc in rats well adapted to physical restraint. This is an abstract of a proposed presentation and does not reflect US EPA policy.