Pre-ischemic exercise preserves cerebral blood flow during reperfusion in stroke

Introduction: The neuroprotective nature of exercise has been well established and the mechanisms of this protection are still a subject of much research. This study aims to determine if cerebral blood flow is constituently higher during the ischemia or reperfusion events in stroke. Materials and methods: Adult male Sprague-Dawley rats were randomly assigned into exercise or nonexercise (control) groups. Exercised rats underwent 30 minutes of running on a treadmill for 3 weeks. A 2 hour unilateral middle cerebral artery occlusion using an intraluminal filament was performed to induce ischemic stroke, followed by a 24 hour reperfusion. A sham control without exercise and middle cerebral artery occlusion was used. Laser Doppler flowmetry (LDF) and O-15-H2O positron emission tomography (PET) were used to determine cerebral blood flow, respectively. F-18-fluorodeoxy-D-glucose was used to determine cerebral metabolism in some animals. Histological analysis determined infarct volume in the same animal after blood flow examination. Results: LDF and PET both indicated that middle cerebral artery occlusion significantly (p<0.05) reduced cerebral blood flow during ischemia and reperfusion in association with reduced cerebral metabolism after stroke. However, pre-ischemic exercise significantly (p<0.05) improved cerebral blood flow during reperfusion, although cerebral blood flow remained at a similar level to that of the non-exercise stroke group during the middle cerebral artery occlusion. This improved cerebral blood flow during reperfusion was associated with decreased brain infarct volume. Conclusions: This study revealed that pre-ischemic exercise in rats improved cerebral blood flow during reperfusion, suggesting that exercise provides neuroprotection by partially ameliorating the 'no reflow' phenomenon in stroke.