HSP70 ACCUMULATION IN TISSUES OF HEAT-STRESSED RATS IS BLUNTED WITH ADVANCING AGE

To determine whether aging results in reduced accumulation of the 70-k Da heat shock protein (HSP70) in response to a thermal challenge, expe riments were conducted in conscious and freely moving mature (12-mo-ol d) and senescent (24-mo-old) male Fischer 344 rats. Rats were assigned to a euthermic control group or a nonexertionally heated group that w as exposed to an ambient temperature of 42 degrees C until colonic tem perature reached 41 degrees C. Samples were subsequently obtained from the liver and myocardium, and absolute levels of both the constitutiv e and inducible forms of HSP70 were quantitated. Heat-stressed rats ha d significantly elevated HSP70 levels in the liver compared with the e uthermic groups. Post hoc comparisons revealed that heat stress elicit ed marked elevations in liver HSP70 in mature rats compared with age-m atched control animals. In contrast, HSP70 values were unchanged in th e senescent heated group vs. the control group. In the myocardium, hea t stress produced marked increases in HSP70 levels in both the mature and senescent groups compared with age-matched control animals, with a ccumulation significantly blunted in the senescent vs. mature rats. Th us the increases in liver and myocardial HSP70 accumulation in respons e to nonexertional heat stress are attenuated with senescence. Because these proteins are postulated to protect cells from injury and enhanc e cellular recovery from heat stress, the data suggest that an aging o rganism has a reduced ability to properly maintain cellular function a nd integrity after a thermal challenge.