高脂饮食诱导幼龄大鼠肝脂肪性变和胰岛素抵抗的发生及二甲双胍的干预作用

目的 通过高脂饮食诱导幼龄大鼠建立非酒精性脂肪性肝病（NAFLD）伴胰岛素抵抗模型,探讨NAFLD幼鼠胰岛素抵抗的发生机制及二甲双胍的干预疗效.方法 将60只3周龄刚离乳雄性SD大鼠按随机数字表法分为3组：对照组、高脂组及二甲双胍组（高脂＋二甲双胍）,每组各20只.对照组予普通饮食,高脂组和二甲双胍组给予高脂饮食5周,同时对照组和高脂组给予生理盐水灌胃,二甲双胍组给予二甲双胍混悬液灌胃（0.25 g·kg-1·d-1）.第5周末从各组大鼠中随机选取12只进行正常血糖-高胰岛素钳夹试验,评价胰岛素敏感性;另8只大鼠处死并取新鲜肝组织进行肝组织病理形态和脂质沉积观察,其中随机取6只通过实时荧光定量PCR分析肝组织中固醇调节元件结合蛋白-1（SREBP-1）、胰岛素受体（IR）、胰岛素样生长因子-1（IGF-1）mRNA的表达.组织学分级差异比较采用秩和检验进行分析.其他指标采用单因素ANOVA分析,两两比较采用LSD法.结果 实验5周后：（1）体重：对照组（316±17）g]、高脂组（202±21）g]、二甲双胍组（171±19）g],3组间两两比较差异有统计学意义（P＜0.01）.（2）病理结果：高脂组大鼠肝脏符合典型的NAFLD病理特征.（3）葡萄糖输注率高脂组、对照组、二甲双胍组分别为（6.51±1.52）、（11.57±1.97）、（13.08±2.33）mg·kg-1·min-1.（4）与对照组相比,高脂组肝组织SREBP-1 mRNA表达较高0.85±0.10比1.67±0.28,P＜0.05],IR mRNA（1.16±0.22）比（0.56±0.22）,P＜0.01]、IGF-1 mRNA（0.87±0.14）比（0.26±0.14）,P＜0.01]表达较低;高脂组与二甲双胍组肝组织SREBP-1 mRNA、IR mRNA、IGF-1 mRNA比较差异无统计学意义（P＞0.05）.结论 高脂饲养5周可建立幼龄SD大鼠NAFLD并发胰岛素抵抗模型,二甲双胍预防可提高机体胰岛素敏感性,其减少NAFLD幼鼠体重的作用与幼鼠体重是否超标可能无关.

Induction of hepatic steatosis and insulin resistance by abundant fat feeding in a young rat model and the effects of metformin intervention

Objective To establish a young rat model of nonalcoholic fatty liver disease (NAFLD)and insulin resistance induced by abundant fat feeding.To investigate the mechanism of insulin resistance and the impact of metformin intervention on fatty liver young rat. Methods Sixty male Sprague-Dawley (SD) rats of 3 weeks old were divided into 3 groups according to random number table: control group,high fat group and metformin group (high fat plus metformin),20 rats in each group.Feed control group with normal calorie diet for 5 weeks while high fat group and metformin group high calorie diet.At the same time,metformin group received an oral metformin suspension (0.25g·kg-1·d-1) while N and HF groups normal saline.At the end of Week 5,12 rats were randomly selected from each group for the technique of hyperinsulinemic euglycemic clamp to evaluate the insulin sensitivity while other 8 rats were executed for histological sections to observe the profiles of hepatic pathologic morphology and fat deposition.Perform Quantitative PCR (polymerase chain reaction) to analyze the hepatic expressions of sterol regulatory element binding protein-1 ( SREBP-1 ) ,insulin receptor (IR) and insulin-like growth factor-1(IGF-1)mRNAs in 6 rats which randomly selected from other 8 rats in each group.Histological grade was examined by Rank Sum test.SREBP-1,IR,IGF-1 and glucose infusion rate(GIR)were analyzed by one-way ANOVA.Results After a 5 weeks: (1) Weight: control group ((316±17)g),high fat group ((202±21)g),metformin group ((171±19)g),pairwise comparisons of the data in the three groups were significantly different (P＜0.01 ).(2) Pathological result: the rat livers in high fat group presented a typical NAFLD pathological alteration.(3) The GIR level of high fat group,control group and metformin group were ( (6.51±1.52),(11.57±1.76),(13.08±2.33)mg·kg-1·min-1)).(4)As compared wiht those in control group,the hepatic expression of SREBP-1 mRNA were higher in high fat group ( (0.85 ±0.10)vs.( 1.67 ±0.28),P＜0.05)) while IR mRNA ((1.16 ±0.22)vs. (0.56 ±0.22),P＜0.01)) and IGF-1 mRNA ((0.87±0.14) vs.(0.26±0.14),P＜0.01)) were lower.There was no difference between the data in high fat group and metformin group( P ＞ 0.05 ).Couclusion A 5-week abundant fat feeding may induce NAFLD and systemic insulin resistance in young SD rat.Metformin intervention can significantly improve the insulin sensitivity,and its effect of weight reduction is irrespective of whether there is overweight or not.