OBJECTIVETo show the changes of heat shock protein 70(HSP70) expression at cellular level in different heat exposure stages and the significance of HSP70 expression in heat exposure organism.

METHODThe heat exposure model was established in rats with artificial hot climatic chamber[34 +/- 1) degree C, RH 60%]. SD rats were randomly divided into control groups(C) and heat exposure groups(A), and into subgroups including 2, 7, 14, 28 d stages from each one of the groups. The immuno-histochemistry was used to detect HSP70 expression in rat liver and cardiac muscle, and photography analytic software was used to analyze HSP70 expression in liver and cardiac cells.

RESULTSThe expression intensity of HSP70 in heat exposure groups(gray values of liver were 137.0 +/- 5.1, 137.0 +/- 5.2, 137.8 +/- 7.1, 139.2 +/- 5.2 respectively; of cardiac muscle 156.1 +/- 4.4, 155.1 +/- 6.2, 155.4 +/- 4.5, 156.2 +/- 5.1 respectively) was stronger than that in control groups(P < 0.01 or P < 0.05) during all stages of the heat exposure; There was no significant difference in expression intensity of HSP70 among various stages of heat exposure; after 2 d of heat exposure, HSP70 expression in cell nuclei of the liver and cardiac muscle cells was stronger than that in cytoplasm in heat exposure group; HSP70 expression in Kupffer's cells of liver was also stronger than that of control(P < 0.05), but not on 7, 14 and 28 d; the activities of alanine aminotransferase(ALT), aspartate aminotransferase(AST), creatine kinase(CK) and hydroxybutyrate dehydrogenase(HBD) showed an increase on 2 d and 28 d of heat exposure.

CONCLUSIONThe vital organs would be damaged on 2 d of heat exposure. High expression of HSP70 at this stage may be a marker of cell damage; Increased HSP70 expression on 7-14 d of heat exposure may play an important role in adaptation to heat, while long term(28 d) heat exposure, the protection of HSP70 from tissue damage may not be enough.