Object: Intracarotid cold saline infusion (ICSI) protects against ischemic stroke not only due to the resulting hypothermia, but also as a result of the cerebral artery flushing. To assess the relative benefit of hypothermia and cerebral artery flushing in neuroprotection, hypothermic and normothermic saline infusions were administrated over a serial time points after the initiation of reperfusion in a rat ischemia model.
Methods: Ischemic strokes were induced in Sprague-Dawley rats (n = 115) by occluding the middle cerebral artery for 2 hours using an intraluminal filament. In the hypothermic groups, the brain temperature was lowered to 33-34°C for 20 minutes by ICSI at three time points (0, 1, and 2 hours) after reperfusion. Correspondingly, in the normothermic groups, the brain temperature was maintained at normal levels during intracarotid normothermic saline infusion (INSI) for 20 minutes at the same time points. After 48-hour reperfusion, infarct sizes and brain water contents were determined using 2,3,5-triphenyltetrazolium chloride (TTC) staining and the dry-wet weight method, respectively. Levels of neuron-specific enolase (NSE), S100beta, and matrix metalloproteinase 9 (MMP9) in the serum were measured by enzyme-linked immunoassay (ELISA). Neurological deficits were also evaluated.
Results: Immediate infusion after the onset of reperfusion (0 hour) did not result in significant difference for reductions of infarct sizes, neurological deficits or S100beta serum levels between ICSI and INSI groups, compared with the non-infusion group. However, brain water content and NSE serum level were significantly lower in the ICSI group than the non-infusion group. When the infusions were started 1 hour after reperfusion, both ICSI and INSI infusions still reduced the infarct sizes, but only ICSI significantly decreased the brain water content, neurological deficits and S100beta serum level. All therapeutic effects of INSI disappeared when infusions were started 2 hours after reperfusion, whereas infarct size, neurological deficits and S100beta serum level were still reduced significantly in ICSI group, compared with the non-infusion group.
Conclusions: The neuroprotection of hypothermia and cerebral artery flushing induced by selective carotid infusion after ischemia weakens as the length of time between the reperfusion and infusion increases. The therapeutic time window of brain hypothermia induced by cold saline infusion is broader than cerebral artery flushing induced by normothermic saline infusion.