[abstract] Hyperbaric Oxygen Blunts Late Rise of Excitatory Neurotransmitters Following Ischemia-Reperfusion Injury in a Rat Model

Abstract

Introduction: It has been demonstrated that hyperbaric oxygen (HBO) decreases the volume of final infarction size following ischemia-reperfusion injury when applied early. The final volume of infarction is increased if HBO is applied greater than 6 hours following injury (1). This study examined the effect of HBO on striatal metabolites using microdialysis at various time intervals following injury. Materials/Methods: Following approval by the institutional animal use committee, 15 male Sprague-Dawley rats were anesthetized and divided into 3 groups, each n=5. A sham group had the left common carotid artery exposed, without MCA occlusion (MCAO). The control group underwent MCAO for 2 hours, followed by reperfusion. The study group underwent MCAO for 2 hours followed by reperfusion, with HBO (100percent O2 at 3ATA for 60 min) applied at 6 hours after reperfusion. Striatal metabolites were measured at 7, 12 and 24 hours following reperfusion using a CMA microdialysis system (CMA AB, Sweden). Samples were analyzed for concentrations of glucose, lactate, pyruvate and glutamate. Data were analyzed by one way ANOVA, p less than 0.05 significant. Results: In controls, glucose and pyruvate increased 10 hours after reperfusion. HBO blunted this increase to almost the pre-occlusion level. Glutamate increased at 7 hours after reperfusion, which was also prevented by HBO. HBO appeared to have no effect on lactate. Conclusions: Excitatory amino acids have been proposed to play a major role in the development of neuronal damage following cerebral ischemia, correlating positively with infarction size (2). This study demonstrated that HBO blunted the rise in glutamate, pyruvate and glucose following ischemia-reperfusion injury. It is possible that the effect of HBO in decreasing infarction size is related to its blunting the elaboration of these striatal metabolites. References: 1) Badr AE, et al. Am J Physiol (in press). 2) Caragine LP, et al. Brain Res 793.