Lamont B J, Andrikopoulos S, Funkat A, Favaloro J, Ye J M, Kraegen E W, Howlett K F, Zajac J D, Proietto J
University of Melbourne Department of Medicine, Royal Melbourne Hospital, 3050 Parkville, Victoria, Australia.
Diabetologia. 2003 Oct;46(10):1338-47. doi: 10.1007/s00125-003-1180-y. Epub 2003 Jul 29.
AIMS/HYPOTHESIS: To study the secondary consequences of impaired suppression of endogenous glucose production (EGP) we have created a transgenic rat overexpressing the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) in the kidney. The aim of this study was to determine whether peripheral insulin resistance develops in these transgenic rats.
Whole body rate of glucose disappearance (R(d)) and endogenous glucose production were measured basally and during a euglycaemic/hyperinsulinaemic clamp in phosphoenolpyruvate carboxykinase transgenic and control rats using [6-(3)H]-glucose. Glucose uptake into individual tissues was measured in vivo using 2-[1-(14)C]-deoxyglucose.
Phosphoenolpyruvate carboxykinase transgenic rats were heavier and had increased gonadal and infrarenal fat pad weights. Under basal conditions, endogenous glucose production was similar in phosphoenolpyruvate carboxykinase transgenic and control rats (37.4+/-1.1 vs 34.6+/-2.6 micromol/kg/min). Moderate hyperinsulinaemia (810 pmol/l) completely suppressed EGP in control rats (-0.6+/-5.5 micromol/kg/min, p<0.05) while there was no suppression in phosphoenolpyruvate carboxykinase rats (45.2+/-7.9 micromol/kg/min). Basal R(d) was comparable between PEPCK transgenic and control rats (37.4+/-1.1 vs 34.6+/-2.6 micromol/kg/min) but under insulin-stimulated conditions the increase in R(d) was greater in control compared to phosphoenolpyruvate carboxykinase transgenic rats indicative of insulin resistance (73.4+/-11.2 vs 112.0+/-8.0 micromol/kg/min, p<0.05). Basal glucose uptake was reduced in white and brown adipose tissue, heart and soleus while insulin-stimulated transport was reduced in white and brown adipose tissue, white quadriceps, white gastrocnemius and soleus in phosphoenolpyruvate carboxykinase transgenic compared to control rats. The impairment in both white and brown adipose tissue glucose uptake in phosphoenolpyruvate carboxykinase transgenic rats was associated with a decrease in GLUT4 protein content. In contrast, muscle GLUT4 protein, triglyceride and long-chain acylCoA levels were comparable between PEPCK transgenic and control rats.
CONCLUSIONS/INTERPRETATION: A primary defect in suppression of EGP caused adipose tissue and muscle insulin resistance.
目的/假设：为了研究内源性葡萄糖生成（EGP）抑制受损的继发性后果，我们培育了一种在肾脏中过表达糖异生酶磷酸烯醇式丙酮酸羧激酶（PEPCK）的转基因大鼠。本研究的目的是确定这些转基因大鼠是否会出现外周胰岛素抵抗。
使用[6-(3)H]-葡萄糖，在基础状态以及正常血糖/高胰岛素钳夹期间，测量PEPCK转基因大鼠和对照大鼠的全身葡萄糖消失率（R(d)）和内源性葡萄糖生成。使用2-[1-(14)C]-脱氧葡萄糖在体内测量各个组织的葡萄糖摄取。
PEPCK转基因大鼠体重更重，性腺和肾下脂肪垫重量增加。在基础条件下，PEPCK转基因大鼠和对照大鼠的内源性葡萄糖生成相似（37.4±1.1对34.6±2.6微摩尔/千克/分钟）。中度高胰岛素血症（810皮摩尔/升）可完全抑制对照大鼠的EGP（-0.6±5.5微摩尔/千克/分钟，p<0.05），而在PEPCK大鼠中则无抑制作用（45.2±7.9微摩尔/千克/分钟）。基础R(d)在PEPCK转基因大鼠和对照大鼠之间相当（37.4±1.1对34.6±2.6微摩尔/千克/分钟），但在胰岛素刺激条件下，对照大鼠的R(d)增加幅度大于PEPCK转基因大鼠，表明存在胰岛素抵抗（73.4±11.2对112.0±8.0微摩尔/千克/分钟，p<0.05）。与对照大鼠相比，PEPCK转基因大鼠的白色和棕色脂肪组织、心脏和比目鱼肌的基础葡萄糖摄取减少，而白色和棕色脂肪组织、白色股四头肌、白色腓肠肌和比目鱼肌的胰岛素刺激转运减少。PEPCK转基因大鼠白色和棕色脂肪组织葡萄糖摄取的受损与GLUT4蛋白含量的降低有关。相比之下，PEPCK转基因大鼠和对照大鼠之间的肌肉GLUT4蛋白、甘油三酯和长链酰基辅酶A水平相当。
结论/解读：EGP抑制的原发性缺陷导致脂肪组织和肌肉胰岛素抵抗。
