EXERCISE HEAT-STRESS IN RATS - PERFORMANCE AND BIOCHEMICAL EFFECTS

Disturbed mental status (DMS) is the most obvious sign of exertional h eatstroke in humans, and is one of the main complications of severe ex ercise heat-stress (SHS). The cause of exertional heat-stroke has been attributed to many factors such as thermoregulatory failure or impair ment of muscular function. This investigation was designed to assess m uscle energy metabolism in two groups of rats running at 34-degrees-C. One group (n = 17) stopped because of DMS (SHS rats), while the other group (n = 21) stopped because of mild or moderate exercise heat-stre ss (MHS rats). SHS rats ran longer and had a higher final rectal tempe rature (T(re)): 66.5 +/- 4.2-degrees-C vs 47.3 +/- 3.8-degrees-C, p < 0.05 and 42.7 +/- 0.12-degrees-C vs 42.2 +/- 0.15-degrees-C, p < 0.05, respectively. SHS rats also had a slower rate of change of T(re) (0.0 54 +/- 0.007-degrees-C min-1 vs 0.072 +/- 0.008-degrees-C min-1) and a lower mean rate of dehydration: 0.065 +/- 0.006 vs 0.084 +/- 0.005 % bodyweight min-1, p < 0.05. There were no significant differences betw een the two groups for skeletal muscle concentration of high energy ph osphates and glycogen, but lactate was higher in SHS than in MHS rats: 25.0 +/- 6.7 vs 11.8 +/- 1.6 mumoles per mg protein respectively, p < 0.05. These data suggest that DMS may be linked to T(re) and that the re is muscular functional impairment caused by SHS.