HSP70 INDUCTION DURING EXERCISE AND HEAT-STRESS IN RATS - ROLE OF INTERNAL TEMPERATURE

The purpose of this study was to determine if the accumulation of the 72-kDa heat shock protein (HSP70) is elevated in response to a prolong ed bout of submaximal exercise in which colonic temperature (T-co) rem ained at control levels. Sprague-Dawley rats were randomly assigned to one of four testing groups [n = 8 per group; ambient temperatures (T- a) for each condition are included]: 1) control (cool/rest; T-a = 24 d egrees C); 2) cool and exercise (cool/exercise; T-a = 14 degrees C; 3) nonexertional heating (heat/rest; T-a = 42 degrees C); 4) heat and ex ercise (heat/exercise; T-a = 32 degrees C). All interventions were sim ilar to 60 min in duration. An exercise bout consisted of treadmill ru nning at 17 m/min and 0% grade, while the heat/rest and heat/exercise experiments consisted of heat exposure that was terminated when T-co r eached 41 degrees C. Baseline T-co was similar for all four groups. In the cool/rest and cool/exercise groups, final T-co was not different from the baseline values, nor was it different between these two group s. In the heat/rest and heat/exercise groups, heating rates were simil ar. Tissue samples were obtained from the gastrocnemius, soleus, and e xtensor digitorum longus (EDL) muscles of the left hindlimb and the le ft ventricle 30 min after a trial was completed. An enzyme-linked immu nosorbent assay specific for HSP70 was used to directly quantitate abs olute levels of HSP70 in tissues. There were significant main effects of both heating and exercise for HSP70 levels in the gastrocnemius, so leus, and left ventricle (P < 0.05). However, in the EDL, neither the heating nor exercise conditions alone produced elevated concentrations of HSP70, although there was a significant interaction of heating and exercise for HSP70 levels in this muscle. In all four tissues sampled , the greatest accumulation of HSP70 was observed in the heat/exercise group. These data indicate that prolonged, submaximal exercise increa ses HSP70 accumulation in locomotor muscles such as the gastrocnemius and soleus muscles and cardiac tissue of rats in a tissue-specific man ner. In addition, the observed increases in HSP70 levels during exerci se were independent of core body temperature, suggesting that factors other than heat stress may contribute to the expression of HSP70 durin g exercise.