Objective   To explore the influence of proteasome inhibitor

MG-132 (N-benz0y1oxycarbonyl(Z)-Leu-Leuleucina1) on the expressions of carboxyl terminus of the Hsc70-interacting protein (CHIP) and heat shock protein 70 (HSP70) in ischemia reperfusion (I/R) rats and investigate the underlying mechanism of myocardial protection by the inhibitor.    Methods   Totally 54 adult SD rats were randomly divided into 3 groups

sham group (n=6)

I/R group (n=24) and treatment group (I/R+T

n=24). The later 2 groups were further equally divided into 3 subgroups according different time of reperfusion. Left anterior descending (LAD) coronary artery was ligated for 30 min and then released for 2 h or 24 h or 7 d in different subgroups. Five minutes before reperfusion

MG-132 at dose of 0.75 mg/kg was given intravenously in I/R+T group，but I/R group and sham group were given the same volume of normal saline. The levels of CHIP and HSP70 at mRNA and protein level were detected by real-time PCR and Western blotting respectively. The correlation between CHIP and HSP70 expression was analyzed.    Results   Compared with I/R groups

the mRNA levels of  CHIP and HSP70 were significantly increased in I/R+T groups (P0.01). Accordingly

the protein expression of them in I/R+T groups were also notably raised compared with I/R groups (P0.01). MG-132 exerted its strongest effect on upregulating the levels of CHIP and HSP70 in mRNA and protein in reperfusion for 2 h. Furthermore

the mRNA and protein levels of HSP70 had significant positive correlation with the expression of CHIP in all groups (r=0.94

P0.01; r=0.89

P0.05).    Conclusion   MG-132 may play a role in myocardial protection by upregulating the expression of CHIP in ischemia reperfusion rats

which then further increases the level of HSP70.