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目的:探讨地塞米松对大鼠肺缺血/再灌注损伤（LIRI）的保护作用及其作用机制。方法:实验一：按随机数字表法将24只SD大鼠分成正常通气组（N组）、生理盐水组（NS组）、LIRI组和地塞米松+ LIRI组（DEX组），每组6只。用血管夹夹闭左肺肺门1 h、再灌注2 h建立大鼠LIRI模型；DEX组于再灌注前5 min经尾静脉给予地塞米松3 mg/kg，NS组注射等量生理盐水；N组不予任何处理。各组于再灌注后2 h处死大鼠取左肺组织，测定肺湿/干重比值（W/D），苏木素-伊红（HE）染色后光镜下观察肺组织病理学改变并评估损伤程度，电镜下观察肺组织超微结构改变；用酶联免疫吸附试验（ELISA）检测肺组织肿瘤坏死因子-α（TNF-α）、白细胞介素（IL-1β、IL-6）水平，用蛋白质免疫印迹试验（Western Blot）检测磷酸化蛋白激酶B（p-AKT）表达。实验二：应用磷脂酰肌醇3 -激酶/蛋白激酶B（PI3K/AKT）通路抑制剂LY294002进行干预，以进一步探讨地塞米松减轻LIRI导致肺组织损伤的作用机制。另取24只大鼠，按随机数字表法分为N组、LIRI组、DEX组、地塞米松+ LY294002+LIRI组（LY组），每组6只。除LY组外，其他组均按实验一方法进行制模及干预，LY组于给予等量地塞米松后尾静脉注射LY294002 0.3 mg/kg。采用免疫组化法检测肺组织中M1型巨噬细胞极化标志物CD11c、CD16以及M2型巨噬细胞极化标志物CD206、Arg1的表达。结果:①实验一：与N组比较，LIRI组肺组织形态学和超微结构发生明显改变，肺病理学评分、肺W/D比值及TNF-α、IL-1β、IL-6水平明显升高，p-AKT表达明显下降。与LIRI组比较，DEX组肺组织形态学和超微结构改变明显改善，肺病理学评分降低（分：5.00±0.89比8.83±0.75），肺W/D比值及TNF-α、IL-1β、IL-6水平明显下降〔肺W/D比值：6.25±0.56比8.27±0.72，TNF-α（ng/L）：93.28±16.42比205.90±25.30，IL-1β（ng/L）：130.10±10.81比209.10±19.20，IL-6（ng/L）：195.80±21.17比310.50±20.77〕，p-AKT表达明显升高〔p-AKT/AKT：（57.58±8.80）%比（36.62±9.25）%〕，差异均有统计学意义（均n P<0.05）。而NS组各指标与N组比较差异均无统计学意义。②实验二：与N组比较，LIRI组巨噬细胞极化标志物CD11c、CD16、CD206、Arg1表达均明显升高。与LIRI组相比，DEX组CD11c、CD16表达明显降低，CD206、Arg1表达明显增加。而给予PI3K/AKT信号通路抑制剂LY294002干预后可明显阻断地塞米松对LIRI介导的巨噬细胞极化的影响〔CD11c免疫组化评分（分）：7.20±0.36比5.00±0.34，CD16免疫组化评分（分）：8.20±0.48比7.40±0.64，CD206免疫组化评分（分）：5.80±0.59比7.40±0.28，Arg1免疫组化评分（分）：7.20±0.72比8.80±0.48，均n P<0.05〕。n 结论:地塞米松预处理可减轻LIRI导致的大鼠肺内炎症反应和肺组织损伤，其作用机制与地塞米松激活PI3K/AKT通路进而改变肺巨噬细胞极化方向有关。“,”Objective:To investigate the protective effect and mechanism of dexamethasone in lung ischemia/reperfusion injury (LIRI) rats.Methods:① Part one experiment: 24 Sprague-Dawley (SD) rats were divided into four groups according to the random number method (n n = 6): standard ventilation group (N group), normal saline group (NS group), LIRI group, and dexamethasone+LIRI group (DEX group). The rat model of LIRI was established by clamping the left pulmonary hilum for 1 hour and reperfusing it for 2 hours. The DEX group was given dexamethasone 3 mg/kg 5 minutes before reperfusion, and NS group was injected with normal saline. Group N did not receive any treatment. The left lung tissue of the rats in each group were taken alive 2 hours after reperfusion. The lung tissue was harvested for lung wet/dry mass ratio (W/D) measurement. Hematoxylin-eosin (HE) staining and electron microscopy was used to observe the pathological changes of lung tissue and to assess the degree of injury. Ultrastructural changes of lung tissue were observed under electron microscope. The levels of tumor necrosis factor-α (TNF-α), interleukin (IL-1β, IL-6) in lung tissue were detected by enzyme linked immunosorbent assay (ELISA). The expressions of phosphorylated protein kinase B (p-AKT) was detected by Western Blot. ② Part two experiment: intervention with phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway inhibitor LY294002 to further explore the mechanism of dexamethasone in reducing lung injury induced by LIRI. Twenty-four SD rats were divided into four groups according to the random number method (n n = 6): N group, LIRI group, DEX group, and dexamethasone+LY294002+LIRI group (LY group). All the groups except the LY group were treated with membrane and intervention according to part one experiment. The LY group was injected with LY294002 0.3 mg/kg after injection of dexamethasone. The expressions of M1 macrophage polarization markers CD11c, CD16, and M2 macrophage polarization markers CD206, Arg1 were detected by immunohistochemistry.n Results:① Part one experiment: compared with N group, the morphological and ultrastructural changes of lung tissue in the LIRI group were significantly changed, lung injury score, lung W/D ratio and TNF-α, IL-1β, IL-6 levels were significantly increased, and p-AKT expression was significantly decreased. Compared with the LIRI group, the morphological and ultrastructural changes of the lung tissue in the DEX group were significantly improved, and the lung injury score was reduced (5.00±0.89 vs. 8.83±0.75), lung W/D ratio and TNF-α, IL-1β, IL-6 levels were significantly decreased [lung W/D ratio: 6.25±0.56 vs. 8.27±0.72, TNF-α(ng/L): 93.28±16.42 vs. 205.90±25.30, IL-1β(ng/L): 130.10±10.81 vs. 209.10±19.20, IL-6 (ng/L): 195.80±21.17 vs. 310.50±20.77], p-AKT expression was significantly increased [p-AKT/AKT: (57.58±8.80)% vs. (36.62±9.25)%], and the differences were statistically significant (alln P < 0.05). There was no significant difference in each index between NS group and N group. ② Part two experiment: compared with the N group, the expression of macrophage polarization markers CD11c, CD16, CD206 and Arg1 in the LIRI group were significantly increased. Compared with the LIRI group, the expressions of CD11c and CD16 in the lung tissue of the DEX group were significantly decreased, and the expressions of CD206 and Arg1 were significantly increased. The intervention of PI3K/AKT signaling pathway inhibitor LY294002 significantly blocked the effect of dexamethasone on LIRI-mediated macrophage polarization (CD11c immunohistochemical score: 7.20±0.36 vs. 5.00±0.34, CD16 immunohistochemical score: 8.20±0.48 vs. 7.40±0.64, CD206 immunohistochemical score: 5.80±0.59 vs. 7.40±0.28, Arg1 immunohistochemical score: 7.20±0.72 vs. 8.80±0.48, all n P < 0.05).n Conclusions:Dexamethasone pretreatment can alleviate the intrapulmonary inflammatory response and lung injury caused by LIRI in rats. The mechanism of action is related to the polarization direction of pulmonary macrophagesvia activation of the PI3K/AKT pathway by dexamethasone.