Cerebrovascular Adaptation after Unilateral Carotid Artery Ligation in the Rat: Preservation of Blood Flow and ATP during Forebrain Ischemia

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Abstract
To investigate long-term adaptations after unilateral carotid artery ligation, the effect of forebrain ischemia on cerebral blood flow and ATP levels was determined at various times after ligation. Unilateral carotid artery ligation was performed in male Wistar rats 0, 3, or 7 days before forebrain ischemia. Laser-Doppler blood flow was monitored bilaterally over the parietal cortex and ATP was measured in the subadjacent cortex of both hemispheres at the end of a 10-minute episode of ischemia. In the 0-day group, forebrain ischemia reduced cortical blood flow to 12% ± 8% (mean ± SD) of preischemic values and lowered cortical ATP to 26% ± 35% of control levels in the ipsilateral hemisphere. Delaying the onset of forebrain ischemia for 3 days after carotid artery ligation significantly improved cortical blood flow (29% ± 12%, P < 0.05) and ATP levels (92% ± 11%, P < 0.05) in the ipsilateral hemisphere. Delaying forebrain ischemia for 7 days also significantly improved ipsilateral blood flow (36% ± 11%, P < 0.05) and ATP levels (81% ± 29%, P < 0.05) compared with the 0-day group. In the contralateral hemisphere, the reduction in blood flow and ATP levels was not significantly altered by delaying the onset of forebrain ischemia for 3 or 7 days. These results show that unilateral carotid artery ligation induces long-term vascular adaptations that improve the collateral circulation and preserve ATP levels during a subsequent episode of ischemia.