OBJECTIVE: To evaluate the effects and mechanism of the Dexmedetomidine on the levels of proinflammatory mediators interleukin 1 beta (IL-1ß) and tumor necrosis factor-α(TNF-α) in ischemia/reperfusion(I/R)rats. METHODS: Fifty healthy SPF male SD rats, 250~310 g,8~12 weeks,were randomly divided into five groups(n=10):sham operation group(sham group),I/R group, dexmedetomidine group(Dex group), atipamezole group(Atip group), dexmedetomidine plus atipamezole(Dex+Atip group). The I/R model was established by clipping hilus of left lung for 30 min and then reperfusion for 2 h. Dex group, Atip group and Dex + Atip group were performed by intraperitoneal injection dexmedetomidine(20 µg/kg),atipamezole(250 µg/kg),Dexmedetomidine(20 µg/kg)+atipamezole(250 µg/kg)respectively 30 min in advance before hilus of left lung was clipped, the rest of the process was the same with I/R group. After the experiment the rats were killed and the left lung tissues to determine the lung wet/dry weight(W/D) and total lung water content(TLW); Ultra structure of lung tissues were observed under light microscope and electron microscope; IL-1ß and TNF-α levels were determined by using ELISA. RESULTS: Compared with the sham group, the W/D、TLW、IL-1ß and TNF-α in other groups were increased significantly (P<0.05). The structure damages of lung tissues observed under light microscope and electron microscope in other groups were more serious than that of sham group. Compared with I/R、Atip、Dex+Atip group, the levels of W/D、TLW,IL-1ß and TNF-α in Dex group were lower (P<0.05), the structure damages of lung tissues observed under light microscopy and electron microscope in Dex group were slighter. There was no significant difference of the above parameters among I/R、Atip、Dex+Atip group. CONCLUSIONS: Dexmedetomidine can alleviate ischemia/reperfusion injury in rat lung through lowering the level of proinflammatory mediators IL-1ß and TNF-α,the possible mechanism may be through stimulation of α2 adrenaline receptors.