DIFFERENTIAL-EFFECTS OF EXERCISE AND HEAT-STRESS ON LIVER HSP70 ACCUMULATION WITH AGING

Previous reports have suggested that the heat shock response to passiv e heating may be blunted by aging. However, during exertional heating, factors in addition to elevated temperature may amplify the degree of stress compared with hyperthermia alone. The purpose of this study wa s to compare the pattern of accumulation of the highly inducible 72-kD a heat shock protein (HSP72) in liver tissue of mature (12-mo-old) and senescent (24-mo-old) male Fischer 344 rats after either passive or e xertional heat stress. A euthermic control group was exposed to an amb ient temperature (T-a) of 25 degrees C for 4.5 h. A passive heating (h eat) group was exposed to an T-a of 42 degrees C until colonic tempera ture (T-co) reached 41 degrees C. An exertional heating (exercise) gro up performed intermittent moderate-intensity treadmill exercise (simil ar absolute intensities for the two age groups) at an T-a of 32 degree s C until T-co reached 41 degrees C. Heating rates were similar in the heat and exercise groups (similar to 0.08 degrees C/min). Rats in bot h the heat and exercise groups were maintained at a T-co of 41 degrees C for an additional 30 min and subsequently returned to an T-a of 25 degrees C for 3 h. Liver HSP72 accumulation was increased in mature ra ts after both the heat (+192% vs. control) and exercise (+292%) protoc ols. In contrast, the senescent rats demonstrated no significant incre ase in inducible HSP70 with heating but a large increase with exercise (+232%; P < 0.01 compared with control and heat groups). These data s uggest that the blunted heat shock protein response to heating observe d with aging is not a result of the inability to produce inducible HSP 72 because older rats had an robust response to exertional hyperthermi a.