Long-term existence of cerebral hypoxic tissue in a rat model of cerebral ischemia/reperfusion injury

BACKGROUND:Hypoxic tissue surrounding the ischemic core may represent the ischemic penumbra following cerebral infarction.However,some studies have shown that the duration of ischemic tissue is longer than previously believed. OBJECTIVE:To clarity whether cerebral hypoxic tissue could survive long-term and whether it is altered in rats following cerebral infarction;to establish an ischemia/reperfusion model in which hypoxic tissue exists for extended periods of time. DESIGN,TIME AND SETTING:A completely randomized grouping and controlled experiment was performed at the Experimental Animal Center of Sun Yat-sen University and Medical Research Center,the Second Affiliated Hospital of Sun Yat-sen University between June and December 2008. MATERIALS:4,9-diaza-3,3,10,10-tetramethyldodecan-2,11-dione dioxime(BnAO)(HL91),used as the hypoxic marker for autoradiography,was supplied by the Beijing Syncor Star Medicinal,China, and the flesh eluent NaTc~mOto mark HL91 was supplied by Guangzhou Medical Isotope Center of the China Institute of Atomic Energy.2-(2-nitro-1H-imidazole-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide(EF5) and its antibody ELK3-51,used as a hypoxic marker for immunofluorescence,were supplied by the University of Pennsylvania,USA. METHODS:Male Sprague Dawley rats were randomly divided into four groups:1.5-hour ischemia/reperfusion group(1.5 h IR),2-hour ischemia/reperfusion group(2 h IR),3-hour ischemia/reperfusion group(3 h IR),and permanent ischemia(PI) group,with 21 rats in each group. The middle cerebral artery occlusion model was established using the intraluminal suture method, while reperfusion was performed by removing the suture at each observation time point.However,in the PI group,the suture was left in the artery. MAIN OUTCOME MEASURES:Area and average absorbance of fluorescence,representing hypoxic tissue,were measured by image-analysis. RESULTS:Autoradiography revealed positive hypoxia at days 1 and 14 postoperatively in the 1.5 h IR group.Immunohistochemistry results demonstrated that hypoxic tissue existed in the 1.5 h IR group on days 1,3,7,and 14,with decay of the area,but no significant weakening of fluorescent intensity.Hypoxic tissues were not observed at day 7 postoperatively in the 2 h and 3 h IR groups, as well as PI group. CONCLUSION:Similar to human cerebral infarction,hypoxic tissues in rats exist for an extended period of time following cerebral infarction,and diminish over even longer periods.Moreover,the 1.5 h IR rat model was the suitable model for studying long-term hypoxic tissue after cerebral infarction.