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Free Radical Reactions after Permanent and Reversible Middle Cerebral Artery Occlusion in Rats

Introduction: In order to observe the production of free radicals, we measured ROS (reactive oxygen species) using X-band electron spin resonance (ESR) spectroscopy with the spin-trapping method. Additionally, we measured the regional cerebral blood flow (rCBF) in ischemic cerebral tissue. We investigated changes in ROS and rCBF in cerebral ischemia and compared pathophysiological differences between permanent ischemia and ischemia-reperfusion groups in rats. Materials and Methods: Cerebral ischemia was produced in rats by occluding the left middle cerebral artery and left common carotid artery. In the permanent ischemia group, occlusion of the arteries continued for 120 minutes, and in the ischemia-reperfusion group, the occlusion was released after 30 minutes. Laser-Doppler flowmetry was used to measure rCBF before and after occlusion of the arteries, and following release of the occlusion. In the permanent ischemia group, ROS was measured 30, 35, 60 and 90 minutes after occlusion of the arteries. In the ischemia-reperfusion group, ROS was measured 5, 30, 60 and 90 minutes after release of the occlusion of the arteries following 30-minute ischemia. ROS was measured by X-band ESR using the PBN (N-tert-butyl-α-phenylnitrone) spin-trapping method. We observed PBN spin adduct signals (relative intensity) and investigated the appearance of ROS in each group. Results: Residual rCBF values in the ischemic cerebral tissue were low and remained at only 17 % of the control level. Values of rCBF increased to 120 % of the control level immediately after reperfusion and remained high for 30 minutes. In ESR measurement, values of ROS production, measured in both the permanent ischemia and ischemia-reperfusion groups, were higher than in the sham group. However, in the permanent ischemia group, ROS production values were unstable and fluctuated during ischemia. On the other hand, in the ischemia-reperfusion group, a steep, short-lasting increase in ROS appeared 5 minutes the reperfusion. C o n c l u s i o n: We demonstrated that ROS was produced in cerebral tissue in both permanent ischemia and ischemiareperfusion. Especially, a burst-like pattern of increased ROS production was found in the cerebral tissue immediately after ischemia- reperfusion. Therefore, in the treatment of acute cerebral ischemic conditions, it is important to bear in mind that ROS production may increase after re-circulation and this may aggravate the condition of the cerebral tissue.