Late reversal of cerebral perfusion and water diffusion after transient focal ischemia in rats.

Region-specific cerebral blood flow (CBF) and the apparent diffusion coefficient (ADC) of tissue water in the rat brain were quantified by high-field magnetic resonance imaging at 9.4 T in the rat suture occlusion model. Cerebral blood flow and ADC were compared during the short- (4.5 hours) and long-term (up to 6 days) reperfusion after 80 minutes of transient middle cerebral artery occlusion, and correlated with the histology analysis. On occlusion, average CBF fell from approximately 100 to less than 50 mL x 100 g(-1) x min(-1) in the cortex, and to less than 20 mL x 100 g(-1) x min(-1) in the caudate putamen (CP). Corresponding ADC values decreased from (6.98 +/- 0.82) x 10(-4) to (5.49 +/- 0.54) x 10(-4) mm2/s in the cortex, and from (7.16 +/- 0.58) x 10(-4) to (4.86 +/- 0.62) x 10(-4) mm2/s in the CP. On average, CBF recovered to approximately 50% of baseline in the first 24 hours of reperfusion. After 2 to 4 days, a strong hyperperfusion in the ipsilateral cortex and CP, up to approximately 300 mL x 100 g(-1) x min(-1), was observed. The ADC ratio in the ipsilateral and contralateral CP was also inverted in the late reperfusion period. Histology revealed more severe tissue damage at the late stage of reperfusion than at 4.5 hours. Significant reversal of CBF and ADC during the late reperfusion period may reflect the impairment of autoregulation in the ischemic regions. Vascular factors may play an important role in the infarct development after 80-minute focal ischemia.