| Part oneMicrodialysis study of the spinal cord during thoracic aort-ic cross-clamping in a porcine modelObjective: Utilize microdialysis to investigate the concentration of amino acid and the changes in energy-related metabolites in spinal cord ischemia. Discuss the mechanism of injury of spinal cord during the ischemia and reperfusion periods.Methods: The experiments were performed in the department of experimental surgery of Fuwai Hospital from October 2003 to May 2004. Six swine were studied. Microdialysis probe was inserted into the lumbar 2 spinal cord to monitor extracellular glucose, lactate, pyruvate, glycerin, glutamate, asparagine, glycin, GABA and taurine during ischemia and reperfusion periods. A left side thoracotomy was performed in the fourth interspace. The descending thoracic aorta as well as the azygos vein was dissected, and the aorta was prepared for cross clamping just distal to the left subclavian artery. After 60 minutes spinal cord ischemia, the clamp was removed. After 90 min reperfusion pathological changes of lumbar segmental (L2) spinal cord were observed with the HE staining.Result: Glucose and pyruvate concentration decreased significantly with the lowest level observed following 60 min of aortic cross clamping. Lactate level increased significantly after aortic clamping. Also the increase of the lactate-pyruvate ratio was observed during aortic cross clamping. There was a significant increase in concentration of Asp, Gly, and GABA after aorta clamping and reperfusion. There was also a significant increase in Glu and Tau after 90 minutes reperfusion. The number of neurons of spinal cord was fewer and degenerative atrophy of spinal cord could be seen by histological examination.Conclusion: Microdialysis reflects the ischemic state of the spinal cord, and is well suited to study each phenomenon. Amino acid plays different roles in the spinal cord ischemia. Glu and Asp may play a key role in the reperfusion injury of spinal cord.
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