Protective Effect And Possible Mechanism Of Losartan On Endotoxin-induced Acute Lung Injury In Rats

Objective:This study was to investigate the protective effect and possible mechanism of losartan on lipolysaccharide(LPS)-induced acute lung injury(ALI)/acute respiratory distress syndrome (ARDS) in rats, with the intervention of losartan, an angiotensin II receptor blockers (ARB), or A779, an angiotensin-(1-7)[Ang-(1-7)] receptor blocker.Method:Made the model of acute lung injury with verus injection of LPS in rats under anesthesia. 50 male Wistar rats were randomly divided into four groups by stochastic number table method:control group, LPS group, LPS plus Losartan group, and LPS+ losartan+A779 group. Under the state of anesthesia, the rats in control group were slowly injected with normal saline (7ml/kg) and continuely pumped normal saline (0.25ml/kg/h) by great saphenous; the rats in LPS group were slowly injected with LPS (7 mg/kg) and continuely pumped normal saline(0.25ml/kg/h); the rats in the LPS+losartan group were injected with LPS (7 mg/kg) slowly and pumped continuely a small amount of losartan(2.5 mg/kg/h); The rats in LPS+losartan+A779 group were injected with A779 (96μg/kg) by tail venous when the experiment started on the basis of the losartan group. The former three groups were observed at 1,4 and 6 h and the fourth group was observed at 4 h, with 5 rats at each time point. Obtained the blood of inferior vena cava, the middle of the right lung and bronchial alveolar lavage fluid (BALF) for detecting. Signs and symptoms of rats in the different groups were paid attention to during the whole process of the experiment; protein in bronchial alveolar lavage fluid and serum was measured by BCA method; the pathological changes in lung tissues were observed with hematoxylin-eosin (HE) staining and the pathological scores were obtained; the contents of AngⅡ and Ang-(1-7) in serum and lung tissue homogenate were assessed by enzyme linked immunosorbent assay (ELISA).Results:1. Compared with control group, the signs and symptoms of the LPS group atl h,4 h, 6 h were fast shallow breathing, audible wheezing sound, cyanosed lips and the endings of limbs,visible pink secretions from nose. Compared with LPS group, the signs and symptoms as above in LPS+Losartan group relieved to different extents.2. Compared with control group, PVPI (BALF total protein/serum total protein) at lh,6h increased significantly (all p<0.01),but unobviously increased at 4h. Compared with LPS group, PVPI in the LPS+Losartan group 1 h,6 h decreased (p<0.01), however increased slightly at 4h.3. Compared with control group, the pathological alterations in lung tissues of rats in LPS group at 1 h,4 h,6 h were obviously aggravated and the lung injury score was dramatically enhanced (all p<0.01).Compared with LPS group, the pathological changes in the LPS+Losartan group lightened and the lung injury score was lower obviously (all p<0.01).4.1) Compared with control group, the contents of serum AngⅡ in LPS group at 1h,4h,6h were all higher, but at 4h was the highest(at 1h,4h p<0.01); Compared with LPS group, the contents of serum AngⅡ in the LPS+Losartan group atlh,4h reduced, however, increased at 6h(all p<0.01).2) Compared with control group, the contents of serum Ang-(1-7) in LPS group at 1h was markedly reduced (p<0.01), at 4h was significantly increased (p< 0.01),and at 6h attenuated under its control levels. Compared with LPS group, the contents of serum Ang-(1-7) in the LPS+Losartan group increased significantly at lh,6h (p<0.01),but decresed slightly at 4h.3) Compared with control group, the contents of lung tissue homogenate AngⅡ in LPS group increased obviously at 1h (p<0.01),4 h,6 h increased slightly. Compared with LPS group, the contents of lung tissue homogenate AngⅡ in the LPS+Losartan group decreased at 1h(p<0.01), increased significantly at 4h (p< 0.01),and increased slightly at 6h. 4) Compared with control group, the contents of lung tissue homogenate Ang-(1-7) 1h,4 h decreased (p<0.01),but increased at 6h(p<0.01). Compared with LPS group, the contents of lung tissue homogenate Ang-(1-7) in the LPS+Losartan group increased at 1h,4h (p<0.01),and decreased slightly at 6h.Conclusions:1. ALI/ARDS model can be successfully copied by Intravenous injection of LPS.2. The RAS is involved in the process of acute lung injury.3. Losartan has a protective effect on LPS-induced acute lung injury in rats, which could improve lung injury in pathology.4. The protection of losartan depends largely on Ang-(1-7) pathway, which can be clarified by A779 intervention.5. The lungs can locally express RAS.