Objective     To observe the effect of sub-hypothermia during ischemia reperfusion on time window for restoration of blood flow and its mechanism.      Methods     One hundred and twenty male rats were randomly divided into sham-operation group (n=10)

24 h middle cerebral artery occlusion (MCAO) group (n=10)

normal temperature (NT) group (n=50)

and sub-hypothermia reperfusion group (n=50).   Twenty-four hours after reperfusion

the animals were killed. Cerebral infarction volume was observed with TTC staining.  A Rat model was established and scored with the Longa scoring system. Water content in brain was measured with the dry-wet weight method. Expressions of AIF

Cyt C

HSP70

MMP-9

and LN were detected by immunohistochemistry.      Results     The cerebral infarction volume

Longa score

expression levels of AIF

Cyt C

HSP70

MMP-9

and LN

water content in brain were significantly different in 24 h MCAO group from those in 2-4 h MCAO group and in different sub-hypothermia reperfusion groups （P0.01）

  but no significant difference was found between 5-6 h MCAO group and 24 h MCAO group

and in 6 h sub-hypothermia reperfusion group after 24 h reperfusion （P0.05）. The cerebral infarction volume

Longa score

and expression levels of MMP-9

AIF

and Cyt C were significantly lower while those of HSP70 and LN were significantly higher in sub-hypothermia reperfusion group than in normal temperature group (P0.05).       Conclusion     Sub-hypothermia during reperfusion can prolong the time window for restoration of blood flow by inhibiting cellular apoptosis and MMP-9 expression

which can alleviate injury of microcirculation and increase the tolerance to reperfusion.