| BACKGROUND and AIMSAcute lung injury (ALI), characterized with a severe and rapid form of microvascular lung injury, is the first stage of acute respiratory distress syndrome (ARDS). Although the mortality from ARDS cases is reducing, approximately 60% of patients with ARDS fail to improve their pulmonary conditions, or get deteriorating even after 1 week ventilation treatment. The lungs in almost all of these patients surviving more than 2 weeks demonstrated a biochemical, and histological evidence of pulmonary fibrosis accompanning with collagen deposition . Progressive hypoxia and multiple organ failure result in up to an 80% mortality in this group. Therefore, our study was desined to observe the pulmonary fibrosis, vascular proliferation and expression of vascular endothelial growth factor (VEGF) in a rat model of acute lung injury, and expect to provide some useful information to the early therapy stratery of ARDS cases.Methods1. The establishment of rat models with oleic acid-induced lung injurySprague-Dawley rats were randomised into control group and oleic acid-induced lung injuried group. The rats were infused via the left femoral vein with oleic acid (100ul/kg) over 1 min. Control animals were treated with an equal volume of saline in a similar manner. OA-treated animals were killed at 1,4,7d after the administration of OA. The right lung was resected, it was insuflated, fixed in 4% formaldehyde polymensatum in PB, embedded in paraffin and cut in 5umthick sections. Hematoxilin and eosin, to determine the type and intensity of the inflammatory response.2. Estimating severity of pulmonary fibrosis on a numerical scaleSections 5um were cut and stained with a modified Masson trichrome to assess the degfee of fibrosis. The Ashcroft scale was used for the quantitative histologic analysis of fibrotic changes induced by OA. The severity of the fibrotic changes in each histologic section of the lung was assessed as a mean score of severity from observed microscopic fields ( X 100 ). After examination of the whole section, the mean of the scores from all fields was taken as the fibrotic score.3. Estimating MVD of lung tissueThe microvascular density (MVD) was determined by the factor 8-related antigen (F8RA). In five adjacent fields of vision in the most vascularized area, microvessels were counted at X200 magnification using an Olympus microscope, remained three greatest value, and then calculated the mean value. MVD was expressed as the mean value of microvessels/sight for each case.4. VEGF MeasurementsPlasma VEGF was measured using a sandwich ELISA kit according to manufacturer's instructions (R&D Systems). Briefly, a monoclonal antibody specific for VEGF was precoated onto a microplate. Standards and samples in duplicate were then pipetted into the wells. After washing, a polyclonal-labeled detection antibody specific for VEGF was added. Following a wash, a substrate solution was added to the wells and color developed in proportion to the amount of VEGF present. The intensity of the color reaction was read spectrophotometrically in a plate reader. The VEGF levels were calculated using a standard curve derived from known concentrations of the respective recombinant proteins.5. Statistical AnalysisAll data are expressed as means +SD Between-group comparisons were done with die nonparametric Mann-Whitney U-test or t-test using SPSS 11.0 version package. Significance was defined as P < 0.05.RESULTS1. Evaluation of rat models of oleic acid-induced lung injuryAfter treated with OA, the animals demonstrate respiratory distress immediatly. PaO2 decreased obviously, lung tissue with hyperemia, severe pulmonary edema..2. Estimating the severity degree of pulmonary fibrosisFibrotic changes were progressive in rat treated with OA after 4 and 7 days of treatment. Histologic examination in normal group, there were neither fiberproliferation nor fibrosis. After 4 and 7 d of OA treatment showed focal fibrotic lesions in lung parenchyma, loss of normal alveolar arc...
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