Effects of hyperglycemia on ischemic brain damage, local cerebral blood flow and ischemic cerebral edema.

The effects of hyperglycemia on ischemic brain damage, local cerebral blood flow (LCBF), and ischemic cerebral edema were studied in a rat model of transient middle cerebral artery (MCA) occlusion with a microclip. Hyperglycemia was induced by intraperitoneal injection of 50% glucose, and same volume of 50% D-mannitol or physiological saline were injected in the controls. LCBF was measured by the quantitative autoradiogram using 14C-iodoantipyrine at 2 hours after MCA occlusion and 2 hours after reperfusion. Cerebrovascular permeability was measured by same technique using 14C-alpha-aminoisobutyric acid (AIB) at 2 hours after reperfusion following 2 hours ischemia. Specific gravity of the brain, determined by the gradient column, was used to study the topographic changes of brain water content at 2 hours after MCA occlusion and 2 hours after reperfusion. Some rats were prepared for neuropathological observation 72 hours after reperfusion. Histological study 72 hours after restoration of CBF following 2 hours MCA occlusion revealed ischemia neuronal cell damage to be more extensive in hyperglycemic rats than in normoglycemic rats. LCBF in the ischemic focus decreased significantly in hyperglycemic rats compared with the controls at 2 hours after MCA occlusion. Furthermore, the reduction of LCBF was observed also in the contralateral non-ischemic side. At 2 hours after reperfusion, in hyperglycemic rats, hyperemia up to 121-156% of the contralateral LCBF was observed within the previously ischemic area, along with a zone of reduced CBF in the surrounding area. At 2 hours after MCA occlusion, the decrease of specific gravity of the ischemic brain, in hyperglycemic rats, was significant compared with the control, and these decreases became more prominent in the entire territory of the MCA at 2 hours after reperfusion. Furthermore, 14C-AIB autoradiogram disclosed the prominent and wide leakage of the tracer within the previous ischemic focus of MCA occlusion. In contrast, in normoglycemic rats, ischemic brain edema showed a reducing trend after reperfusion, and no demonstrable changes of cerebrovascular permeability were disclosed on autoradiograms. These findings suggest that the enhancing mechanisms of hyperglycemia for ischemic brain damage are severely reduced CBF during ischemia and postischemic vasogenic edema.