基础研究 Open Access
Copyright ©The Author(s) 2003. Published by Baishideng Publishing Group Inc. All rights reserved.
世界华人消化杂志. 2003-07-15; 11(7): 982-985
在线出版日期: 2003-07-15. doi: 10.11569/wcjd.v11.i7.982
早期肠道营养减轻烧伤后肠黏膜损伤的机制研究
彭毅志, 袁志强, 肖光夏
彭毅志, 袁志强, 肖光夏, 中国人民解放军第三军医大学西南医院烧伤研究所重庆市 400038
彭毅志, 男, 1958-08-17生, 重庆市人, 汉族, 1983年, 第三军医大学本科毕业, 1993年第三军医大学博士毕业, 主任医师, 教授, 博士导师, 主要从事烧伤感染及创面修复的研究.
通讯作者: 彭毅志, 400038, 重庆市, 中国人民解放军第三军医大学西南医院烧伤研究所. yizhipen@mail.tmmu.com
电话: 023-68754173 传真: 023-65320896
收稿日期: 2002-08-02
修回日期: 2002-08-10
接受日期: 2002-08-16
在线出版日期: 2003-07-15

目的

探讨早期肠道营养在减轻烧伤后肠黏膜损伤中的作用机制.

方法

通过建立大鼠肠淋巴瘘模型, 随机将大鼠分为早期肠道营养组、烧伤对照组和单纯手术对照组, 动态观察了烧伤前及伤后3, 6, 12, 24 h大鼠肠淋巴液流量、肠淋巴液中丙二醛(MDA)和超氧化物歧化酶(SOD)含量、内毒素含量及肿瘤坏死因子(TNF)含量.

结果

烧伤后肠淋巴液流量及SOD含量明显下降(P<0.05), 早期肠道营养组肠淋巴液流量及SOD含量显著高于烧伤对照组(P<0.05); 烧伤后肠淋巴液内毒素、MDA及TNF含量明显升高(P<0.05), 早期肠道营养组肠淋巴液内毒素、MDA及TNF含量显著低于烧伤对照组(P<0.05); 早期肠道营养组和烧伤对照组肠淋巴液MDA与内毒素含量呈显著正相关(rA组 = 0.95, rB组 = 0.93, P<0.01); 肠淋巴液内毒素与TNF含量也呈显著正相关(rA组 = 0.91, rB组 = 0.98, P<0.01).

结论

早期肠道营养可通过改善肠黏膜缺血缺氧, 减轻氧自由基引起的肠黏膜损伤以及阻断内毒素-炎性递质-肠黏膜损伤这一恶性循环, 从而保护了肠黏膜屏障, 减少了肠源性感染的发生.

关键词: N/A
引文著录: 彭毅志, 袁志强, 肖光夏. 早期肠道营养减轻烧伤后肠黏膜损伤的机制研究. 世界华人消化杂志 2003; 11(7): 982-985
Effects of early enteral feeding on intestinal mucosa injury in burned rat
Yi-Zhi Peng, Zhi-Qiang Yuan, Guang-Xia Xiao
Yi-Zhi Peng, Zhi-Qiang Yuan, Guang-Xia Xiao, Institute of Burn Research, Southwest Hospital, Third Military Medical University, Chongqing 400038 China
Correspondence to: Dr. Yi-Zhi Peng, Instituteof BurnResearch, SouthwestHospital, ThirdMilitaryMedicalUniversity, Chongqing400038 China. yizhipen@mail.tmmu.com
Received: August 2, 2002
Revised: August 10, 2002
Accepted: August 16, 2002
Published online: July 15, 2003

AIM

To analysis the mechanism of early enteral nutrition extenuating the damage of intestinal mucosa in burned rats.

METHODS

Lymphatic fistula of intestine was created in Wistar rats, the rats were then sustained with 30% TBSA third degree scald and divided randomly to early enteral nutrition, non early enteral nutrition and operation control groups. The content of malondialdehyde(MDA), superoxide dismutase (SOD), endotoxin and tumor necrosis factor (TNF) in intestinal lymph and intestinal lymph flow were observed dynamically.

RESULTS

After burns the intestinal lymph flow and SOD were significantly decreased(P<0.01); the level of intestinal lymph endotoxin, MDA and TNF were evidently increased (P<0.05). However, the early enteral nutrition could increase the intestinal lymph flow and SOD (P<0.05), decrease the levels of intestinal lymph endotoxin, MDA and TNF (P<0.05). The level of intestinal lymph MDA was positively related to the endotoxin level and the endotoxin level was positively related to the TNF level in early enteral nutrition and simply burn groups.

CONCLUSION

Oxygen-derived free radicals are one of the factors of intestinal mucosal damage after burns, and the early enteral nutrition could protect the intestinal mucosal barrier from being injured and inhibit the bacterial translocation from the intestine.

Key Words: N/A
0 引言

严重创伤、烧伤、出血性休克、肠梗阻及高热等均可削弱肠黏膜屏障功能, 肠腔内存在的大量微生物和内毒素侵入体循环, 从而形成肠源性感染. 后者与顽固性休克、难以控制的早期暴发性败血症及多器官功能衰竭(MOF)的发生发展密切相关[1-4]. 近年来早期肠道营养在防治肠源性感染中的作用引起越来越多的注意[5-16]. 我们通过观察烧伤后大鼠肠淋巴液流量、肠淋巴液中丙二醛(MDA)和超氧化物歧化酶(SOD)含量、内毒素含量及肿瘤坏死因子(TNF)含量, 对早期肠道营养在减轻烧伤后肠黏膜损伤中的作用机制进行了探讨.

1 材料和方法
1.1 材料

健康Wistar大鼠146只(第三军医大学动物所提供), 雌雄各半, 质量250±20 g. 腹腔麻醉下, 于大鼠右肾静脉平面, 肠系膜动脉旁找到肠淋巴管, 插入去热原的聚乙烯管(外径: 0.8 mm, 内径: 0.5 mm), 见淋巴液经引流管流出后予以妥善固定. 肠淋巴管造瘘成功后, 于胃前壁作浆肌层荷包缝合, 暂不结扎, 在荷包缝线中央用尖刀片切开胃壁, 置入硅胶管(外径: 1.5 mm, 内径: 0.8 mm), 通过幽门插入小肠约2 cm, 结扎荷包缝线固定胶管后将其经腹壁引出, 缝合腹壁切口. 术后将大鼠放入限制笼[17]. 术后24 h, 大鼠肠淋巴液流量趋于稳定. 禁食5h后腹腔麻醉, 将大鼠背部剃毛, 置剃毛区于92 ℃水中18 s, 造成30% TBSA Ⅲ度烧伤. 伤后立即腹腔注入平衡液40 mL/kg. 仍将大鼠放入限制笼内饲养.

1.2 方法

随机将146只大鼠分为3组, 最后有48只大鼠成功用于本研究. 早期肠道喂养组(A组, n = 14): 致伤后20 min内开始肠道喂养营养液(Eusure, 美国产, 每毫升营养液含1 kcal热量. 热卡分布为: 蛋白质14%, 脂肪31.5%, 碳水化合物54.5%.)180 mL/kg·24 h. 使用LDB-H型微量电子蠕动泵经胃造瘘管24 h持续均匀输入; 烧伤对照组(B组, n = 14): 用等量复方乳酸林格氏液代替营养液, 其他处理同A组; 单纯手术对照组(C组, n = 20): 仅行肠淋巴管造瘘和胃造瘘, 但不致伤, 自由进食. 观察记录致伤前和伤后3, 6, 12, 24 h肠淋巴液流量, 并收集淋巴液. 肠淋巴液标本收集和内毒素测定所用的所有器材均经蒸馏水清洗、烘干, 高压蒸气消毒后用60Co照射去热原. 按各时相点取肠淋巴液, 500 r/min离心5 min, 吸取上清液, 采用基质偶氮显色法鲎试验测定其内毒素含量, 由上海市医学化验所提供试剂盒, 严格按说明书操作. 肠淋巴液MDA和SOD测定: 按各时相点取肠淋巴液, 3 000 r/min离心10 min, 吸取上清液, 采用南京铁道医学院提供的MDA和SOD试剂盒, 按说明书操作测定肠淋巴液中MDA和SOD含量. 肠淋巴液TNF测定: 采用双抗体夹心法(ELISA), 由军事医学科学院提供TNF试剂盒, 严格按说明书操作.

统计学处理 采用SPLM软件包对实验数据进行处理, 包括t检验和相关性分析.

2 结果

烧伤对照组(B组)伤后3 h肠淋巴液流量明显下降, 持续到伤后24 h(P<0.05); 早期肠道营养组(A组)虽然肠淋巴液流量也明显低于单纯手术对照组(C组)(P<0.05), 但显著高于烧伤对照组(P<0.05), 早期肠道营养组伤后各时相点肠淋巴液流量比烧伤对照组约高一倍(表1).

表1 烧伤后大鼠肠淋巴液流量变化(mean±SD, mL/h).
分组nPBH
0361224
A 组140.78±0.100.43±0.09ac0.48±0.17ac0.40±0.11ac0.31±0.09ac
B 组140.78±0.110.19±0.05a0.29±0.04a0.17±0.03a0.15±0.03a
C 组200.79±0.150.78±0.140.82±0.170.76±0.110.67±0.06
aP <0.05 vs C组;
cP <0.05 vs B组.
2.1 肠淋巴液内毒素含量

烧伤对照组(B组)大鼠肠淋巴液内毒素含量伤后3 h即显著增高, 12 h达高峰, 持续到伤后24 h (P<0.05); 早期肠道营养组(A组)伤后各时相点肠淋巴液内毒素含量明显低于烧伤对照组(P<0.05), 但仍显著高于单纯手术对照(C组, 表2).

表2 肠淋巴液内毒素、MDA、SOD及TNF含量变化.
指标分组nPBH
0361224
内毒素(Eu/ml)A 组140.19±0.040.48±0.08ac0.61±0.05ac0.72±0.09ac0.52±0.07ac
B 组140.19±0.041.47±0.14a1.52±0.17a1.90±0.23a1.80±0.22a
C 组200.19±0.040.19±0.040.20±0.040.19±0.030.21±0.0 6
MDA(nmol/L)A 组148.04±1.9720.00±2.46ac26.10±2.04ac23.73±2.71ac19.77±2.62ac
B 组149.23±1.6855.30±4.15a77.92±10.05a66.31±10.39a66.72±6.40 a
C 组209.02±1.948.75±1.999.24±1.939.31±1.928.34±1.78
SOD(NU/L)A 组14265±26193±30ac182±29ac198±23ac231±32ac
B 组14259±24106±22a131±32a157±33a196±28a
C 组20256±29255±25263±26253±23262±24
TNF(ng/L)A 组140.62±0.061.47±0.09ac1.58±0.10ac1.54±0.12ac1.95±0.16ac
B 组140.62±0.063.73±0.20a3.90±0.18a4.07±0.16a4.11±0.23a
C 组200.62±0.070.61±0.080.58±0.170.59±0.050.64±0.05
aP <0.05 vs C组;
cP <0.05 vs B组.
2.2 肠淋巴液MDA、SOD含量的变化

烧伤后各时相点肠淋巴液MDA含量均高于单纯手术对照组(C组), 烧伤对照组(B组)肠淋巴液中MDA含量明显增高, 伤后6 h达高峰, 伤后24 h仍高于正常(P<0.05); 早期肠道营养组(A组)烧伤后MDA升高的幅度显著低于烧伤对照组(P<0.05). 烧伤对照组(B组)肠淋巴液中SOD含量于伤后3 h即下降到最低点, 持续到伤后24 h(P<0.05); 而早期肠道营养组(A组)肠淋巴液中SOD含量烧伤后各时相点均显著高于烧伤对照组(P<0.05), A、B两组伤后各时相点SOD含量均显著低于单纯手术对照组(表2).

2.3 肠淋巴液TNF含量的变化

烧伤后肠淋巴液中TNF含量明显高于正常, 烧伤对照组(B组)肠淋巴液中TNF含量在伤后3 h即开始升高, 伤后24 h达高峰, 伤后各时相点TNF含量均显著高于单纯手术对照组(P<0.05); 早期肠道营养组(A组)伤后各时相点TNF含量均显著低于烧伤对照组(P<0.05, 表2).

烧伤后早期肠道营养组(A组)和烧伤对照组(B组)肠淋巴液MDA与内毒素含量的增加呈显著正相关(r A组 = 0.95, r B组 = 0.93, P<0.01); 肠淋巴液内毒素与TNF含量的增加也呈显著正相关(r A组 = 0.91, r B组 = 0.98, P<0.01).

3 讨论

肠道是微生物和内毒素含量最高的器官, 在正常情况下机体具有多种防御功能, 以防止其进入全身组织和器官. 当机体受到严重创伤时, 由于肠黏膜屏障功能受损, 肠道菌群紊乱及机体免疫功能受抑, 这些防御机制可能被破坏, 导致肠道内的细菌和内毒素通过肠淋巴管或门静脉移位, 进而引起全身性感染[18]. 严重烧伤后, 机体为了保护心脑等重要器官而减少内脏的血流量, 使肠黏膜处于低灌流状态, 从而导致肠黏膜屏障功能的损害. 本结果显示, 烧伤对照组伤后各时相点肠淋巴液流量显著减少, 而早期肠道营养组则比烧伤对照组的肠淋巴液流量高一倍左右. 提示烧伤后早期肠道营养可以明显改善肠黏膜缺血缺氧状态. 烧伤后肠黏膜缺血再灌流时可产生大量的氧自由基(O2-), 后者主要作用于细胞膜, 使之发生脂质过氧化, 破坏组织细胞. 已有资料表明氧自由基参与了烧伤后肠黏膜损伤[19,20]. 本结果表明, 烧伤后各时相点肠淋巴液中MDA(一种脂质过氧化代谢产物)的含量均显著增高, 早期肠道营养组肠淋巴液中MDA含量明显低于烧伤对照组, 而且MDA含量与内毒素含量呈显著正相关. 提示: 反映肠黏膜屏障损伤的指标MDA在烧伤后明显增加, 导致肠淋巴液中肠源性内毒素增加; 早期肠道营养减少了氧自由基的产生, 维护了肠黏膜结构的完整性, 降低了肠淋巴液中内毒素含量.

肠道中的微生物在突破肠道免疫屏障的过程中, 内毒素可以触发多种炎性递质释放, 包括TNF、血小板活化因子(PAF)及氧自由基等[20-30]. 本研究结果显示: 烧伤后3 h肠淋巴液中TNF含量即达较高水平, 至伤后24 h一直呈上升趋势; 早期肠道营养组肠淋巴液中TNF含量增加的幅度显著低于烧伤对照组. 相关分析的结果表明, 内毒素与TNF的水平呈显著正相关. 提示: 烧伤后肠淋巴液TNF含量的增加与内毒素的增加有关; 由于减少了烧伤后肠道内毒素的移位, 所以使TNF的水平下降. 烧伤后肠源性内毒素移位能引起大量炎性递质释放, 这些内毒素、炎性递质反过来又可影响肠黏膜微循环, 破坏组织细胞氧的传递, 进一步增加肠黏膜屏障的损害, 我们将这一过程称之为内毒素-炎性递质-肠黏膜损伤的恶性循环. 早期肠道营养由于减少了肠道细菌和内毒素移位, 因此及时阻断了这一恶性循环, 不仅减轻了内毒素和炎性递质对于肠黏膜的继续损伤, 而且还可避免可能发生的多器官功能衰竭.

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