Aging reduces adaptive capacity and stress protein expression in the liverafter heat stress

A decline in an organism's ability to cope with stress through acute respon se protein expression may contribute to stress intolerance with aging. We i nvestigated the influence of aging on stress tolerance and the capacity to synthesize the 70-kDa heat shock protein (HSP70) in young and old rats expo sed to an environmental heating protocol. Livers were assessed for injury a nd HSP70 expression after heat stress by use of immunohistochemical and imm unoblotting techniques. The inducible HSP70 response in the cytoplasm and n ucleus was markedly reduced with age at several time points over a 48-h rec overy period, although senescent rats were able to strongly express HSP70 e arly in recovery. Older animals had extensive zone-specific liver injury, w hich corresponded to the diminished HSP70 response observed in these region s, and a significant reduction in thermotolerance compared with their young counterparts. These data high light the regional nature of stress-induced injury and HSP70 expression in the liver and the impact of aging on these r esponses. Furthermore, the results suggest a functional link between the ag e-related decrements in the expression of inducible HSP70 and the pathophys iological responses to heat stress.