急性肺损伤幼鼠肺泡Ⅱ型上皮细胞和SP-A变化相关性的研究

目的：该实验旨在研究急性肺损伤（ALI）时肺泡Ⅱ型上皮细胞（AEC-Ⅱ）超微结构变化和肺组织表面活性蛋白SP-A含量的变化关系，从而探讨ALI的发病机制。方法：48只Sprague-Dawley幼鼠被随机分为正常对照组和ALI组。 腹腔注射脂多糖（LPS，4 mg/kg）建立ALI模型，正常对照组注射等量生理盐水。 LPS注射后24，48，72 h每亚组各处死8只大鼠。 取左肺下肺组织待透射电镜检查。 用Western blot方法测定肺组织SP-A的相对含量。结果：ALI 24 h时，AEC-Ⅱ微绒毛消失。24 h及48 h时板层小体（lamellar body, Lb）数量增加，体积增大，密度减低，排空明显增强，呈指环状绕核排列，细胞增生活跃，代谢旺盛。48 h时Lb呈巨大空泡样变性。肺组织SP-A含量明显高于对照组（24 h时ALI组为6.52±0.62，对照组为5.02±0.35， P< 0.01；48 h时ALI组为6.65±0.62，对照组为5.01±0.36，P< 0.01）。72 h时Lb破溃，数目明显减少，细胞核形态不规则，部分核边界不清，肺组织SP-A含量下降(ALI组为3.87±0.50，对照组为5.22±0.36，P<0.01)。结论： LPS致幼鼠ALI时AEC-Ⅱ和肺组织SP-A的变化为时间依赖性，随AEC-Ⅱ损伤程度的加重肺组织SP-A由代偿转为失代偿，可能是发生ARDS的重要机制之一。

Relationship between alveolar epithelial type II cells and pulmonary surfactant protein A levels in young rats with acute lung injury

OBJECTIVE: This study examined the relationship between the ultrastructural alterations of alveolar epithelial cells type II (AEC-II) and pulmonary surfactant protein A (SP-A) levels in the lung tissue of young rats with acute lung injury (ALI) in order to explore the possible mechanism of ALI. METHODS: Forty-eight young Sprague-Dawley rats were randomly divided into control and ALI groups. The rats in the ALI group were intraperitoneally injected with 4 mg/kg of lipopolysaccharide (LPS) in order to induce ALI. The control subjects were injected with the same volume of normal saline. Rats were sacrificed at 24, 48 and 72 hrs after LPS or NS injection. Lung samples were obtained from the lower parts of the left lung and fixed with 2.5% glutaraldehyde for transmission electron microscope examination and for Western blot test of SP-A. RESULTS: The microvilli of AEC-II disappeared 24 hrs after LPS injection. After 24 and 48 hrs of LPS injection, lamellar body (Lb) increased in number, enlarged in size and reduced in density, and the ring-like arrangement of Lb was present. By 48 hrs after LPS injection, giant Lb with vacuole-like deformity appeared. The contents of lung SP-A in the ALI group 24 hrs (6.52+/-0.62 vs 5.02+/-0.35P<0.01) and 48 hrs (6.65+/-0.62 vs 5.01+/-0.36P<0.01) after LPS injection were significantly higher than those in the control group. By 72 hrs after LPS injection, Lbs ruptured and were reduced in number. The shape of the nuclei was irregular and the border was blurred. The content of lung SP-A was greatly reduced in the ALI group 72 hrs after LPS injection compared with that in the control group (3.87+/-0.50 vs 5.22+/-0.36; P<0.01). CONCLUSIONS: The alterations of AEC-II and lung SP-A were time-dependent in young rats with ALI induced by LPS. In the early stage of ALI, the lung SP-A content showed a compensatory increase. With the increasing injury of AEC-II cells, the secretion of SP-A presented with a decompensation and the lung SP-A content decreased. This may be one possible mechanism for the development of ARD.