Induction of translational thermotolerance in liver of thermally stressed rats

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.