Effects of moderate hypothermia on leukocyte-endothelium interaction in the rat pial microvasculature after transient middle cerebral artery occlusion

Background and Purpose-It has been demonstrated that moderate hypothermia a ttenuates brain damage, but the mechanism whereby this is achieved has not been clearly shown. Recently, the role of leukocytes as mediators of second ary brain damage after brain ischemia has been discussed. The aim of this s tudy is to examine the effects of moderate hypothermia on leukocyte-endothe lium interaction in the rat pial microvasculature after transient middle ce rebral artery occlusion (MCAO). Methods-Rhodamine 6G-labeled leukocytes in brain surface were visualized wi th intravital fluorescence videomicroscopy through a closed cranial window. We analyzed the number of leukocytes adhering to the venular and arteriola r endothelium before ischemic insult and up to 3 hours after reperfusion. R ats were divided into 4 experimental groups. Group I (n=6) consisted of sha m-operated animals. Groups II (n=6) and III (n=6) received left MCAO for 1 hour under normothermia (36 degrees C to 37 degrees C, group II) and under moderate hypothermia (30 degrees C to 32 degrees C, group III). Group IV (n =4) received left common carotid artery occlusion for 1 hour under normothe rmia. Results-The number of adhering leukocytes in venules in groups II and IV in creased significantly (P<0.001) after reperfusion compared with the group I , but that in group III did not increase significantly (P>0.05). The number of adhering leukocytes in arterioles in group II increased significantly ( P<0.01) compared with the other groups, although the adhering leukocytes we re not as numerous as those seen in venules. Conclusions-It is demonstrated that hypothermia attenuates adhering leukocy tes in venules and arterioles after reperfusion of MCAO. The inhibition of the leukocyte function may be an important factor in the neuroprotective ef fect of hypothermia.