EXERCISE PERFORMANCE OF NORMOTHERMIC AND HYPERTHERMIC RATS - EFFECT OF WARM REARING

1. Hypothalamic and rectal temperatures were recorded in 8 warm-reared (wr) and 12 control rats. Rats ran to exhaustion at a constant speed of 1.5 km h-1 but at a variable ambient temperature adjusted to stabilize their hypothalamic temperature at 38.0-degrees-C (normothermia) or 41.0-degrees-C (hyperthermia). Blood lactate concentrations were determined before and after exercise. 2. Exercise caused exhaustion in normothermic control rats after 62.08 +/- 5.43 min and in wr rats after 29.64 +/- 2.09 min. 3. Hyperthermia shortened to one half (to 12.24 +/- 1.36 min) and to one fourth (to 16.15 +/- 1.20 min) the endurance time in wr and control rats, respectively. 4. There were no correlations between lactate concentration and hyperthermia or endurance time. 5. In conclusion, in rats and other animals which have safe refuges, hyperthermia interferes with the ability to continue exercising.