Objective To evaluate the effects of dexmedetomidine on lung ischemia-reperfusion (I/R) injury in rats.Methods Ninety-six healthy SPF male Wistar rats,weighing 250-350 g,aged 8-12 weeks,were randomly divided into 4 groups (n =24 each):sham operation group (S group),I/R group,low dose dexmedetomidine group (DL group) and high dose dexmedetomidine group (DH group).In DL and DH groups,dexmedetomidine 100 and 500 μg· kg-1 · d-1 were injected intraperitoneally once a day for 2 consecutive days,while the equal volume of normal saline was given in S and I/R groups.Lung·I/R was induced by clamping the left hilum of lung for 45 min followed by reperfusion at 30 min after administration on 2nd day.At 45 min of ischemia,and 60 and 120 min of reperfusion,6 rats were sacrificed,and lungswere removed for determination of TNF-α (tumor necrosis factor-a) content and myeloperoxidase (MPO) activity in lung tissues.The percentage of damaged alveolar in lung tissues was detected at 120 min of reperfusion.Another 6 rats were lavaged and the broncho-alveolar lavage fluid (BALF) was colleted for determination of the total protein concentrations.Results Compared with S group,the TNF-α content,MPO activity,percentage of damaged alveolar,and total protein concentrations in BALF were significantly increased in I/R,DL and DH groups.Compared with I/R group,the TNF-α content,MPO activity,percentage of damaged alveolar,and total protein concentrations in BALF were significantly decreased in DL and DH groups.Conclusion Dexmedetomidine can alleviate the lung I/R injury in rats,and the mechanism is related to inhibiton of the inflammatory responses.