Induction of translational thermotolerance in liver of thermally stressed rats

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Abstract
Heat-shock gene expression in cultures of single cell types has been well characterized but little is known about the heat-shock response of intact organs in vivo. In this study, the kinetics of hepatic heat-shock gene expression and the induction of thermotolerance were characterized in rats. Animals were subjected to a defined, reversible stress by increasing the core body temperature to 41°C or 42°C for 30 min. New synthesis of the inducible form of the heat shock-70 family of proteins (hsp-72) peaked simultaneously with the maximal level of hsp-72 transcripts at both temperatures. These data are consistent with previous observations in cultures of hepatoblastoma cells after thermal stress [De Maio, A., Beck, S. C. & Buchman, T. G. (1993) Circ. Shock 40, 177–186]. The incorporation of radioactive amino acids into polypeptides by the liver was blocked during the first hour of recovery after heat shock at 42°C. This inhibition of protein synthesis by thermal stress could be prevented by prestressing rats at 42°C for 30 min and allowing the rats to recover for 24 h at normal body temperature (37°C). This phenomenon, previously defined as ‘translational thermotolerance’, correlates with the hepatic content of hsp-72; maximal protection occurs 24 h after a 42°C thermal stress when hsp-72 (protein) is also maximum and decreases with the clearance of hsp-72 from the liver. These data suggest that the presence of hsp-72 within the liver may modulate the organ response to subsequent stresses and may be important to organ and animal survival after repeated insults.