高脂饮食肥胖大鼠胰岛细胞胰岛素抵抗机理的探讨

A study on the mechanism of islet cell insulin resistance in high-fat-diet obese rats

目的探讨高脂饮食诱导的肥胖大鼠在具有外周胰岛素抵抗(IR)的情况下,胰岛胰岛素、胰高血糖素的分泌和合成功能,高糖刺激下胰高血糖素和胰岛素的分泌以及胰岛内胰岛素信号转导分子的改变。方法30只雄性Wistar大鼠随机分为高脂饲料喂养的肥胖组和普通饲料喂养的对照组,每组各15只,共喂养20周。采用胰腺组织匀浆,检测胰岛素和胰高血糖素的含量;胰岛细胞表面灌注检测高糖状态胰岛素和胰高血糖素的动态分泌变化;免疫组织化学染色及图像分析检测胰岛素受体(IRc)及胰岛素受体底物1、2(IRS1、IRS2)在两组大鼠胰岛的表达。结果(1)肥胖组胰岛素敏感指数(ISI)明显低于对照组,肥胖组血胰高血糖素水平和胰岛内的胰高血糖素水平均显著高于对照组(362pg/ml±58pg/mlvs291pg/ml±35pg/ml,P<0.05;442pg/ml±56pg/mlvs287pg/ml±48pg/ml,均P<0.05)。(2)肥胖组葡萄糖刺激的胰岛素分泌(GSIS)受损,16.7mmol/L葡萄糖可显著抑制对照组胰岛α细胞胰高血糖素的分泌,而在肥胖组这种抑制作用消失。(3)胰岛存在IRc、IRS1和IRS2的表达。肥胖组胰岛IRc、IRS2的表达较对照组胰岛分别低28%和22%(均P<0.01)。结论高脂饮食诱导的肥胖大鼠胰岛细胞的胰岛素信号转导通路受损,即在有外周IR的同时也具有胰岛内的IR,这可能是肥胖状态下胰岛细胞功能障碍的内在机制之一。

Objective To study the changes of insulin signal transduction in islet cells of high-fat-diet rats with peripheral insulin resistance (IR). Methods Thirty male Wistar rats were randomly divided into 2 equal groups: high-fat-diet group and control group to be fed with high-fat food and normal food respectively. Twenty weeks after the rats were sacrificed. The contents of insulin and glucagon in homogenate of pancreas were detected during islet cell perifusion, and insulin receptor (IRc) and insulin receptor substrates (IRS-1 and IRS-2) were detected by immunohistochemistry. Results (1) The insulin sensitive index (ISI) was significantly decreased in the high-fat-diet rats in comparison with the normal rats, while the contents of glucagon in blood and in homogenate of pancreas were both significantly increased in the high-fat-diet rats (362 pg/ml±58 pg/ml vs 291 pg/ml±35 pg/ml;442 pg/ml±56 pg/ml vs 287 pg/ml±48 pg/ml, both P<0.05). (2) The glucose stimulated insulin secretion (GSIS) was impaired in the high-fat-diet rats. 16.7 nmol/L glucose could inhibit the glucagon secretion by the α cells of the normal rats, but not of the high-fat-diet rats. (3) The expression of IRc, IRS-1 and IRS-2 in islets was stronger in the peripheral cells (non-insulin secretion cells) than in the center cells(insulin secretion cells). The expression of IRc and IRS-2 was significantly decreased by 28% and 22% respectively in the high-fat-diet rats compared with the normal controls (both P<0.01). Conclusion High-fat-diet rats have impairment of insulin signal transduction in islet cells, which may contribute to the insulin resistance of islet α and β cells and explain, at least in part, the dysfunction of the islet cells under peripheral IR.