Characteristics of pulmonary function and pathological changes following acute lung injury in rats

Objective To investigate the characteristics of pulmonary function and pathological changes in rats with acute lung injury (ALI) and provide experimental basis for further study on the mechanism of ALI. Methods Twenty five male SD rats were randomly divided into the control group (n=5) and acute lung injury (ALI) group (n=20). Lipopolysaccharide (LPS) (4.5 mg/kg) were injected into the ALI group rats to establish the ALI rat model. The rats in control group were given 150 μl isotonic saline. At 12, 24, 48, and 72 hours after injury, lung function of the rats were tested by Buxco small animal lung function test system, including the dynamic lung compliance (Cdyn), forced vital capacity (FVC), functional residual gas (FRC), quasi static compliance (Cchord), 100th millisecond expiratory volume (FEV100), and airway resistance (RI). In addition, the bronchoalveolar lavage fluid (BALF) was collected for detection of protein level and tumor necrosis factor (TNF-alpha) concentration. At the same time, the changes of lung tissues were recorded, and the pathological changes were observed by HE staining. Results Compared with the control group, Cdyn, FVC, FRC, and FEV100 in ALI group were significantly decreased at each time point after injury (P 0.05). The protein level and TNF-alpha concentration of BALF in ALI group were increased significantly (P<0.05 or <0.01) 12-72 hours after injury (P<0.01). Compared with the control group, the whole lung was dark red in ALI group 12 hours after injury, and the most serious bleeding occurred in the pulmonary hilum area with single or multiple hemorrhagic foci of different sizes. Multiple punctate and focal bleeding of different sizes were seen on the lung surface, which were radially distributed around the pulmonary hilum. The color of lung tissue was gradually restored to normal at 72 hours after injury. Under the light microscope, pulmonary interstitial edema, inflammatory cell infiltration, pulmonary vascular congestion and focal pulmonary hemorrhage were observed 12 h after injury, showing typical ALI pathological changes. The pathological changes were the most significant at 24 hours and reduced obviously at 72 hours. Conclusions A single intratracheal injection of LPS can induce typical ALI pathological changes. There is a similar trend between the pulmonary function indexes, lung pathology characteristics, and the protein level of BALF and proinflammatory cytokine level, suggesting that the pulmonary function test parameters can provide reference for evaluation of ALI. Key words: Lipopolysaccharide; Acute lung injuries; Respiratory function tests; Tumor necrosis factor α