Heat-induced acute hyperthermia results in a reversible depression of cold defence in the rat ( Rattus norvegicus)

Abstract

1. 1. Adult female Wistar rats were made hyperthermic (colonic temperature, T c, of 41 to 42°C for 60 min) by external heating and then tested for their autonomic cold defence (cold exposure of 15°C for 45 min) either immediately after hyperthermia or 2 h later. 2. 2. Compared with cold defence of normothermic controls, hyperthermic rats showed a decreased cold-induced thermogenesis and a fall in the body temperature threshold for its elicitation, both resulting in a greater reduction in T c. 3. 3. Two to three days after hyperthermia all measured parameters of cold defence returned to the normal values observed before hyperthermia. 4. 4. The reversible depression of cold defence demonstrated by the present study can be interpreted as a sign of adaptive modification in thermoregulation, probably helping recovery from hyperthermia.