目的：肺表面活性物质蛋白D(SP-D)被认为是急性肺损伤(ALI)和急性呼吸窘迫综合征(ARDS)有价值的生物指标,但在急性肺损伤早期,肺组织SP-D的变化特征仍不清楚。该研究旨在探究脂多糖(LPS)诱导的SD幼鼠急性肺损伤时SP-D,SP-D mRNA的时序变化及肺泡Ⅱ型上皮细胞及板层小体的超微结构的变化。方法：腹腔内注射LPS建立急性肺损伤模型。注射后6,12,24,36,48,72 h各处死8只大鼠。W estern b lot和RT-PCR方法测定肺组织SP-D和SP-D mRNA的含量。透射电子显微镜研究肺泡Ⅱ型上皮细胞超微结构的变化。结果：LPS注射12 h后SP-D和SP-D mRNA含量均开始下降。SP-D mRNA于注射LPS后24~36 h降到最低。SP-D在48 h达最低点。透射电镜显示急性肺损伤组板层小体出现多样变形,特别是在注射后48 h。LPS导致板层小体的体积增大、数量减少,伴有大量空泡样变。结论：在LPS诱导的急性肺损伤的早期SP-D的波动变化呈时间依赖性。肺组织SP-D在48 h时水平最低,此时伴有肺泡Ⅱ型上皮细胞严重的多形性变。在ALI发病初期,肺组织低水平的SP-D与较差的临床预后有关。

OBJECTIVE: Pulmonary surfactant protein-D(SP-D) is regarded as a valuable biomarker in acute lung injury(ALI) and acute respiratory distress syndrome (ARDS), but the alterations of SP-D in lung tissues in the early course of ALI remain unknown.This study was designed to explore the temporal fluctuations of SP-D and SP-D mRNA in young rats with ALI induced by lipopolysaccharide(LPS),as well as the alterations of ultrastructures of alveolar type Ⅱ(ATⅡ) cells. METHODS: Rat ALI models were established by intraperitoneal injection of LPS (4 mg/kg). The rats were sacrificed at 6,12, 24, 36, 48 and 72 hrs after LPS injection (8 rats each time point). Western blot and RT-PCR were employed to detect the contents of SP-D and SP-D mRNA in lung tissues. The ultrastructures of ATⅡcells were studied with transmission electron microscopy. RESULTS: Both SP-D mRNA and SP-D levels decreased after 12 hrs of LPS administration. The SP-D mRNA level reached a nadir at 24-36 hrs, but the SP-D level was reduced to its nadir by 48 hrs after LPS administration.LPS resulted in the alterations of lamellar bodies (LBs) in size (multilamellar forms), density(vacuole-like deformity) and number. The alterations of ultrastructures of ATⅡcells were most significant at 48 hrs. The clinical symptoms of ALI rats were most severe at 48 hrs. CONCLUSIONS: The alterations of the SP-D level were time-dependent in the early course of LPS-induced ALI. The lowest level of SP-D occurred at 48 hrs while severe multideformities of ATⅡcells were presented. A decreased level of SP-D in the lungs in the early stage of ALI may be associated with a worse clinical outcome.