Research in Medicine

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Background: Recent studies suggest that normobaric hyperoxia (HO) results in ischemic tolerance to reduce ischemia brain injury. In this research, attempts were made to assess threshold of ischemic tolerance induced by normobaric hyperoxia in rat stroke model. Materials and methods: Rats were divided into two groups and each group into four experimental groups, each containing 21 animals. The first four groups were exposed to 95% inspired Ho for 4h, 8h, 16h, and 24 hr. The second four groups acted as controls, and were exposed to 21% oxygen in the same chamber (room air, RA) continuously for 4h, 8h, 16h, and 24h. All animals were subjected to 60min right middle cerebral arterial occlusion (MCAO) 24h after pretreatment. After 24h reperfusion, each main group was subdivided to three subgroups (n=7) for assessment of neurologic deficit score (NDS), infarct volume, Evans blue (EB) extravasations, and brain water contents. Results: Preconditioning with 16HO and 24HO decreased NDS and infarct volume significantly. Ischemic tolerance induced by 24 HO decreased EB extravasations significantly. Preconditioning with 4HO, 8HO, 16HO and 24 HO could not decrease brain water content significantly. Conclusion: Although further studies are necessary to clarify the mechanisms of ischemic tolerance, the lowest Ho duration for ischemic tolerance induction is 16h, but appropriate Ho duration for ischemic tolerance induction is 24 HO.

Keywords: Normobaric Hyperoxia, Brain ischemia tolerance, Stroke, Neuroprotection, Blood-brain permeability, brain water content.

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