Normobaric oxygen inhibits AQP4 and NHE1 expression in experimental focal ischemic stroke

The aim of the present study was to determine the effect of 60% normobaric oxygen (NBO) on neurological function, brain edema and the expression of hypoxia‑inducible factor‑1α (HIF‑1α), aquaporin 4 (AQP4) and Na+/H+ exchanger 1 (NHE1) in a rat model of cerebral ischemia‑reperfusion injury. Male Sprague‑Dawley rats underwent transient focal cerebral ischemia via right middle cerebral artery occlusion (MCAO) for 120 min followed by 48 h of reperfusion. The rats were exposed to NBO at 60 and 100% or no treatment during reperfusion for 48 h. Neurological impairment score (NIS) was evaluated prior to the sacrifice of all rats. Hematoxylin‑eosin staining was performed after 48 h of reperfusion with NBO treatment. The infarct volume and brain water content (BWC) were determined to assess brain ischemic injury at 24 and 48 h. The levels of HIF‑1α, AQP4 and NHE1 expression in brain tissue samples were determined by western blotting and reverse transcription‑quantitative polymerase chain reaction analysis. During reperfusion, the protein and mRNA expression of HIF‑1α, AQP4 and NHE1 increased over time (up to 48 h). Exposure to 60 and 100% NBO during reperfusion following MCAO improved NIS, and alleviated BWC and infarct volume after 24 and 48 h, with further improvements in the 100% NBO group, compared with 60%. Additionally, the molecular mechanisms involved in the effects of NBO may be associated with reduced AQP4 and NHE1 expression and increased HIF‑1α expression. However, 60% NBO therapy during reperfusion following an acute ischemic stroke did not achieve the same effects as 100% NBO. Further experimental studies should be performed to elucidate the mechanism and beneficial effects of 60% NBO, as it is more cost‑effective to use, compared with 100% NBO.