Chronic mild reduction of cerebral perfusion pressure induces ischemic tolerance in focal cerebral ischemia.

BACKGROUND AND
PURPOSE: Neurons acquire tolerance to ischemic stress when preconditioning ischemia occurs a few days beforehand. We focused on collateral development after mild reduction of perfusion pressure to find an endogenous response of the vascular system that contributes to development of ischemic tolerance.
METHODS: After attachment of a probe, the left common carotid artery (CCA) of C57BL/6 mice was occluded. The left middle cerebral artery (MCA) was subsequently occluded permanently on days 0, 1, 4, 14, and 28 (n=8 each). The change in cortical perfusion during MCA occlusion was recorded. A sham group of mice received only exposure of the CCA and MCA occlusion 14 days later. In apoE-knockout mice, the MCA was occluded 14 days after CCA occlusion or sham surgery. Infarct size and neurologic deficit were determined 4 days after MCA occlusion.
RESULTS: Mice that had 45% to 65% of baseline perfusion after CCA occlusion were used. Cortical perfusion after MCA occlusion was significantly preserved in day 14 (47+/-16%) and day 28 (46+/-7%) groups compared with day 0 (28+/-8%), day 1 (33+/-19%), day 4 (29+/-16%), and sham groups (32+/-9%). Infarct size and neurologic deficits were also attenuated in day 14 and day 28 groups compared with other groups. In apoE-knockout mice, there was no significant difference in perfusion, neurologic deficits, or infarction size between groups with and without CCA occlusion.
CONCLUSIONS: Chronic mild reduction of perfusion pressure resulted in preservation of cortical perfusion and attenuation of infarct size after MCA occlusion. These responses of collaterals were impaired in apoE-knockout mice.