Evaluation of Cerebral Blood Flow Autoregulation during Early Phase

Reperfusion following brain ischemia is associated with releasing of different substances influencing the cerebrovascular diameter, which can alter cerebrovascular autoregulation as a homeostasis mechanism of brain blood flow. The present study was considered to evaluate the effect of transient focal cerebral ischemia on the brain blood flow autoregulation during early phase of reperfusion. The experiment was performed on 12 rats that divided into two groups; sham and ischemic groups, n=6 for each group. In ischemic group, transient focal cerebral ischemia was induced with 60 min middle cerebral artery occlusion (MCAO) followed by 12 hr reperfusion. Regional cerebral blood flow (rCBF) was continuously recorded during experiment and lesion volume of right hemisphere was determined by tri-phenyl tetrazolium chloride (TTC) staining method 12 hr after termination of MCAO. Autoregulation of ischemic region was measured 30 min after beginning of reperfusion by transient increasing of blood pressure (intravenous injection of phenylephrine 0.01 g in10 mL saline with increasing 0.1μg/min) and simultaneous recording of rCBF in ischemic region. The means of cerebral blood flow in the ischemic regions was reduced by 80% in ischemic group compared with sham. Also ischemia/reperfusion induced infarction in a large area of right hemisphere in ischemic group (326±5 mm3). Increasing of arterial pressure from 90 mmHg to 170 mmHg did not change the focal cerebral blood flow of sham. But in ischemic group enhancing of arterial pressure up to 90 mmHg increased the blood flow of the ischemic regions. The findings of this study indicated that cerebrovascular autoregulation of ischemic region severely damage at the early phase of reperfusion following brain ischemia, which results in intensification of brain ischemia injury.