成年期追赶生长对大鼠胰岛素敏感性与应激水平的影响

目的 观察成年期追赶生长对大鼠胰岛素敏感性和应激水平的影响,并探讨其胰岛素抵抗形成的可能机制。方法 将7周龄雄性SD大鼠分为6组（共2个时间点）,即4周时间点2组：热卡限制4周组(R4),正常饮食4周组(NC4)作为R4组对照;8周时间点4组：正常饮食追赶生长组(RN4)、高脂饮食追赶生长组(RH4)、持续高脂饮食8周组（HF8）、持续正常饮食8周组(NC8)。通过先热卡限制后恢复饮食的方法建立追赶生长大鼠模型。检测大鼠高胰岛素-正糖钳夹试验过程中葡萄糖输注率和骨骼肌2-脱氧葡萄糖摄取、胰岛素刺激后的骨骼肌胰岛素信号通路、血皮质酮、骨骼肌11β-羟类固醇脱氢酶1(11β-HSD1)表达水平。结果 热卡限制4周时,R4组大鼠血皮质酮和骨骼肌11β-HSD1 mRNA表达水平明显高于NC4组(P＜0.05),骨骼肌蛋白激酶B( Akt) Ser473磷酸化和糖摄取与NC4组相比差异无统计学意义。热卡限制后恢复饮食4周时,血皮质酮和骨骼肌11β-HSD1表达水平RN4组明显高于NC8组,RH4组明显高于NC8和HF8组,而骨骼肌Akt磷酸化和糖摄取RN4组明显低于NC8组,RH4组明显低于NC8组、HF8组和RN4组（均P＜0.05）。结论正常饮食和高脂饮食追赶生长大鼠均可导致整体和骨骼肌应激水平上调及胰岛素抵抗,尤以高脂饮食追赶生长大鼠更为明显。应激和饮食状况的交互作用可能是追赶生长胰岛素抵抗形成的重要原因。     

姜黄素促进骨骼肌GLUT4转位改善糖尿病大鼠胰岛素抵抗

目的研究姜黄素对STZ诱导糖尿病大鼠骨骼肌胰岛素抵抗的影响及其机制。方法雄性SD大鼠腹腔注射STZ诱导糖尿病大鼠模型。成模大鼠分为糖尿病组(DM),糖尿病+姜黄素组(DM+Cur),糖尿病+缓冲液对照组(DM+NC)。以正常SD大鼠为正常对照组(NC)。DM+Cur组予姜黄素灌胃治疗,DM+NC组给予等体积缓冲液灌胃。连续给药12周。12周后检测血糖变化,高胰岛素-正葡萄糖钳夹试验检测外周胰岛素抵抗。实验结束处死大鼠,取骨骼肌提取总蛋白及细胞膜蛋白,Western blot法检测骨骼肌磷酸化PI3K及AKT和总PI3K及AKT水平,检测骨骼肌总GLUT4及细胞膜上GLUT4水平,免疫荧光检测骨骼肌细胞膜上GLUT4水平。多组间的比较采用单因素方差分析,评估PI3K、AKT磷酸化程度及GLUT4向细胞膜转位的变化。结果姜黄素治疗组血糖水平低于糖尿病组[(18.67±1.99对24.38±2.88)mmol/L,P<0.05],胰岛素抵抗较糖尿病组减轻[平均GIR(14.69±0.29对10.25±0.30)mg·kg-1·min-1,P<0.01],胰岛素信号通路中p-PI3K、p-AKT水平升高,GLUT4向细胞膜转位增多。结论姜黄素通过激活PI3K/AKT通路,促进GLUT4向细胞膜转位,增加骨骼肌葡萄糖摄取,最终改善胰岛素抵抗。     

运动干预对胰岛素抵抗大鼠骨骼肌超微结构的影响及其临床意义

目的 观察胰岛素抵抗(IR)大鼠骨骼肌超微结构变化的特点,探讨高脂饮食及运动对骨骼肌的影响. 方法 健康Wismr雄性大鼠分基础饲料喂养组(NC),高脂饲料喂养组(HF).高脂喂养大鼠10周,构建IR动物模型.HF组再随机分出一半为非运动组,另一半为运动组,游泳运动干预4周.运动前后以钳夹技术评估IR大鼠胰岛素敏感性,检测3组大鼠葡萄糖输注率(GIR)以及股薄肌进行透射电镜观察. 结果 HF组大鼠GIR显著低于NC组(P<0.01),运动组大鼠GIR显著低于非运动组(P<0.01);电镜显示,HF组骨骼肌细胞肌原纤维束排列松散;线粒体数量减少;运动后可明显减轻上述病理改变. 结论 运动可增强骨骼肌的有氧代谢,改变IR大鼠骨骼肌超微结构,并以线粒体改变较为明显.适当的运动能够改善IR机体内胰岛素敏感性,维持骨骼肌细胞的正常形态.     

高脂饮食对老年大鼠骨骼肌脂肪酸含量及乙酰辅酶A羧化酶表达和活性的影响

目的 探讨增龄和高脂饮食对大鼠骨骼肌脂肪酸含量及乙酰辅酶A羧化酶(acetyl-coenzyme A carboxylase,ACC)表达和活性的影响.方法 将22～24月龄雄性Wistar大鼠随机分为老年对照组和高脂组;4～5月龄大鼠作为青年对照组.老年对照组和青年对照组给基础饲料,高脂组给予高脂饲料,喂养8周.用高胰岛素-正葡萄糖钳夹实验评价各组大鼠胰岛素敏感性,用全自动生化分析仪测定骨骼肌三酰甘油,用荧光分光光度计测定骨骼肌总的长链脂酰辅酶A含量,用Western-blot方法测定骨骼肌ACC、和磷酸化ACC(P-ACC)蛋白表达.结果 (1)老年对照组空腹血糖、胰岛索和游离脂肪酸高于青年对照组,高脂组上述几项指标进一步升高,并且出现血清三酰甘油和总胆固醇水平增高;(2)老年对照组葡萄糖输注率(glucose infusion rates,GIR)低于青年对照组,高脂组GIR低于老年对照组,高脂组GIR在8周末低于4周末;(3)老年对照组骨骼肌三酰甘油及长链脂酰辅酶A含量高于青年对照组,高脂组与老年对照组比较进一步升高;(4)老年对照组与青年对照组之间、高脂组与老年对照组之间骨骼肌ACC蛋白表达均无明显变化(P>0.05);骨骼肌P-ACC蛋白水平在老年对照组低于青年对照组,高脂组与老年对照组比较进一步降低(P<0.05或P<0.01).结论 与青年大鼠比较,老年大鼠更易出现脂肪酸代谢异常及胰岛素抵抗;高脂饮食导致老年大鼠骨骼肌脂质积聚更加严重,ACC活性的改变可能在骨骼肌脂质堆积和胰岛素抵抗发生中起了一定作用.     

高脂喂养及罗格列酮干预对老年大鼠骨骼肌核呼吸因子1表达的影响

目的 观察高脂饮食和罗格列酮干预对老年大鼠骨骼肌核呼吸因子1(NRF-1)表达及葡萄糖输注率的影响.方法 21～23月龄Wistar大鼠分为老年对照组、高脂组和高脂+罗格列酮干预组(干预组),并设 4～5月龄Wistar大鼠作为青年对照组.应用正常葡萄糖高胰岛素钳夹技术测得葡萄糖输注率,以评价胰岛素敏感性,高脂喂养第8周时,检测骨骼肌NRF-1 mRNA表达.结果 高脂喂养8 w后青年对照组、老年对照组和高脂组空腹血游离脂肪酸、三酰甘油及骨骼肌三酰甘油均升高,葡萄糖输注率下降;经过罗格列酮干预后上述三组游离脂肪酸、三酰甘油及骨骼肌三酰甘油均明显下降,葡萄糖输注率升高.与青年对照组比较,老年对照组骨骼肌NRF-1的表达下降,经高脂喂养后NRF-1的表达进一步下降,干预组NRF-1表达高于高脂组(P<0.01),但仍比老年对照组的表达低(P<0.01).结论 高脂饮食可诱导老年大鼠产生IR及骨骼肌 NRF-1表达下降,罗格列酮可能调节骨骼肌NRF-1的表达.     

罗格列酮对胰岛素抵抗大鼠骨骼肌腺苷酸活化蛋白激酶α表达及活性的影响

目的 探讨罗格列酮对胰岛素抵抗大鼠骨骼肌脂肪酸代谢及腺苷酸活化蛋白激酶(AMP-activated protein kinase,AMPK)α表达和活性的影响.方法 根据随机数字表将40只4～5月龄雄性Wistar大鼠随机分至健康对照组(n=16;给予基础饲料)和高脂喂养组(n=24;给予高脂饲料).喂养4周末,两组各取8只大鼠行高胰岛素.正葡萄糖钳夹实验,评价高脂喂养组胰岛素抵抗状态.造模成功后根据随机数字表将高脂喂养组(n=16)随机分至高脂喂养亚组(n=8)和罗格列酮干预亚组(n=8),继续喂以高脂饲料4周,罗格列酮干预亚组同时给予3 mg·kg-1·d-1罗格列酮灌胃.骨骼肌甘油三酯经氯仿-甲醇抽提后采用全自动生化分析仪测定.运用实时荧光定量逆转录聚合酶链反应方法 测定骨骼肌AMPKα1及AMPKα2 mRNA表达水平;运用聚丙烯酰胺凝胶电泳和Western blot方法 测定骨骼肌AMPKα1、AMPKα2及P-AMPKα蛋白表达水平.组间比较采用完伞随机设计的单因素方差分析.结果 第8周末,高脂喂养亚组葡萄糖输注率低于健康对照组[分别为(19.3±3.7)和(30.4±4.2)mg·kg-1·min-1,P<0.01],罗格列酮干预亚组葡萄糖输注率高于高脂喂养亚组[分别为(25.8±1.6)和(19.3±3.7)mg·kg-1·min-1,P<0.05].高脂喂养亚组骨骼肌甘油三酯含量高于健康对照组[分别为(4.4±1.2)和(2.0±0.5)μmol/g,P<0.01],罗格列酮干预亚组骨骼肌甘油三酯含量低于高脂喂养亚组[分别为(3.3±1.1)和(4.4±1.2)μmol/g,P<0.05].骨骼肌AMPKαl mRNA及蛋白表达无组问差异(P>0.05);骨骼肌AMPKα2 mRNA、蛋白表达和P-AMPKα蛋白表达高脂喂养亚组低于健康对照组,而罗格列酮干预亚组高于高脂喂养亚组(均P<0.05).结论 高脂饮食可导致大鼠骨骼肌脂质堆积及胰岛素抵抗.罗格列酮干预可增加胰岛素抵抗大鼠骨骼肌AMPKα2表达和AMPKα活性,降低骨骼肌脂质含量,提高胰岛素敏感性.     

胰岛素抵抗大鼠骨骼肌中蛋白激酶B表达及葡萄糖转运蛋白4转位的改变

目的研究高脂饮食喂养的胰岛素抵抗(IR)大鼠骨骼肌中蛋白激酶B(PKB)表达和葡萄糖转运蛋白4(GluT4)转位的改变及饮食治疗、葛根素、罗格列酮干预的影响。方法将雄性SD大鼠50只随机分为正常饮食(A)组和高脂饮食(B)组,2个月后再将B组大鼠随机分为高脂饮食(C)组、正常饮食干预(D)组、葛根素干预(E)组和罗格列酮干预(F)组。干预1个月后检测骨骼肌中PKB的表达及转位至质膜的GluT4含量。结果C组大鼠产生了明显的IR,骨骼肌中PKB的表达较A组显著降低(P<0.01),转位到质膜上的GluT4含量显著减低(P<0.01);D、E、F组大鼠IR明显改善,骨骼肌中PKB的表达较C组大鼠显著增加(P<0.01),GluT4含量较C组大鼠显著升高(P<0.01)。结论高脂饮食喂养的SD大鼠骨骼肌产生明显的IR,骨骼肌中Ins诱导的PKB表达降低,Ins刺激的GluT4向质膜的转位减少。饮食治疗及葛根素、罗格列酮干预能增加骨骼肌中Ins刺激的PKB表达及GluT4向质膜的转位。     

Irisin通过激活AMPK促进C2C12细胞葡萄糖摄取

目的研究鸢尾素(irisin)对C2C12细胞葡萄糖摄取的影响及机制。方法将C2C12细胞分为:Control组,不同浓度的irisin组(分为0.1μg/ml,0.3μg/ml和1μg/ml组),高糖/高脂(HG/HF)处理组,HG/HF+不同浓度的irisin组(分为0.1μg/ml,0.3μg/ml和1μg/ml组),Control+Scramble siRNA组,HG/HF+AMPKα2 siRNA组,HG/HF+scramble siRNA组,HG/HF+scramble siRNA+irisin组,HG/HF+AMPKα2 siRNA+irisin组。采用荧光葡萄糖(2-NBDG)检测细胞的葡萄糖摄取;Western blot检测细胞葡萄糖转运体4(GLUT4)转位情况和AMPK磷酸化水平。结果 (1)与Control组相比,HG/HF组C2C12细胞葡萄糖摄取降低(P0.05),不管是否经过高糖处理,Irisin均增加C2C12细胞葡萄糖摄取(P0.05或P0.01)。与Control组相比,HG/HF降低鼠骨骼肌细胞膜GLUT4表达(P0.01),Irisin显著增加HG/HF孵育骨骼肌细胞细胞膜GLUT4表达(P0.01);(2)与Control组相比,HG/HF降低C2C12细胞细胞膜AMPK磷酸化水平(P0.05),在Control组及HG/HF组,Irisin显著增加骨骼肌细胞AMPK的磷酸化水平(P0.05);(3)与HG/HF+scramble siRNA+irisin组相比,HG/HF+AMPKα2 siRNA+irisin转染组细胞葡萄糖摄取及细胞表面GLUT4表达均显著减少(P0.05或P0.01)。结论 Irisin通过激活AMPK促进小鼠骨骼肌细胞葡萄糖摄取。     

追赶生长大鼠胃泌素及内脏脂肪细胞CCK2R表达变化

24只Wistar大鼠分为正常对照组、限食组、追赶生长组,检测所有大鼠血糖、血脂、血清胃泌素,内脏脂肪体脂比、脂肪细胞CCK2R mRNA和蛋白水平.结果 显示限食组和正常组相比,血清胃泌素水平降低54%(P＜0.05),内脏脂肪体脂比减少55%(P＜0.05),脂肪细胞CCK2R mRNA和蛋白表达下降(2.19±0.18对3.2±0.24,0.11±0.03对0.15±0.04,P＜0.05).追赶生长组血清胃泌素水平分别高于限食组72%和正常组31%(P＜0.05),内脏脂肪体脂比高于限食组114%(P＜0.05),达到正常对照组水平;同时脂肪细胞CCK2R mRNA和蛋白表达高于正常对照组(4.09±0.59对3.2±0.24,0.25±0.05对0.15±0.04,P＜0.05).追赶生长大鼠内脏脂肪优先沉积的机制可能和胃泌素分泌增加及脂肪细胞CCK2R表达增加相关.

Abstract：

Wistar rats(n=24) were divided into normal control group(NC), food restriction group(FR), and catch-up group(RN). Serum glucose,lipids, gastrin, the ratio of visceral fat to body fat, adipocyte CCK2R mRNA and protein levels were determined. Compared with NC group, FR rats had lower serum gastrin and visceral fat formation. The adipocyte CCK2R mRNA and protein levels of FR rats were lower than those of NC rats. Serum gastrin level of RN rats was higher than those of FR and NC rats(P＜0.05). The ratio of visceral fat to body fat in RN rats increased compared with FR rats and was close to that of NC rats. The adipocyte CCK2R mRNA and protein levels of RN rats were higher than those of FR and NC rats. Gastrin and its receptor pathway possibly play a role in the mechanism of visceral fat accumulation in catch-up rats.     

罗格列酮上调高脂饮食老年大鼠骨骼肌GLUT4和PKB的表达

目的 观察高脂饮食对老年大鼠骨骼肌葡萄糖转运蛋白4(GLUT4)和蛋白激酶B(PKB)的表达变化及罗格列酮的干预效果.方法 老年大鼠随机分为对照组、高脂组(HF)、高脂+罗格列酮干预组(RSG),每组20只.应用清醒状态下正常葡萄糖高胰岛素钳夹技术的葡萄糖输注率评价胰岛素抵抗,用荧光定量PCR法和Western印迹技术检测骨骼肌GLUT4和PKB的表达.结果 高脂组骨骼肌长链脂酰辅酶A(LCACoA)升高而葡萄糖输注率明显下降(P＜0.01),骨骼肌GLUT4和PKB的表达明显降低(P＜0.05,P＜0.01),罗格列酮干预组显著缓解高脂组上述变化(P＜0.05,P＜0.01).结论 罗格列酮上调高脂饮食老年大鼠骨骼肌GLUT4和PKB的表达,是改善老年胰岛素抵抗的机制之一.     

Effect of cold acclimation on the expression of glucose transporter Glut 4.

Glucose uptake by brown adipose tissue, measured following deoxyglucose injection in vivo, was increased by 6- and 11-fold following 2 and 14 days of cold exposure, respectively. To look for the possible mechanism of these modifications, the glucose transporter Glut 4 has been characterized at the protein and mRNA levels in brown adipose tissue, skeletal muscle and white adipose tissue following cold acclimation. Crude membranes were prepared from those tissues, and Glut 4 was studied by Western blot analysis. In brown adipose tissue, the total Glut 4 amount was increased by 52 +/- 7% and by 104 +/- 12% following 2 and 14 days of cold exposure, respectively. By contrast, in white adipose tissue of 14-day-cold-exposed mice the total Glut 4 content was decreased by 42 +/- 5%. However, Glut 4 concentration, expressed per mg of membrane protein, was unchanged in both brown and white adipose tissues following cold exposure, since the membrane protein content increased in brown but decreased in white adipose tissue. No modification in Glut 4 content was observed in skeletal muscle from cold-exposed mice. Total RNA were prepared and analyzed for Glut 4, glyceraldehyde phosphate dehydrogenase (GAPDH) and actin. Glut 4 and GAPDH mRNA were increased 2-fold in brown adipose tissue from cold-exposed mice, while actin mRNA content was unmodified. Glut 4 mRNA content was not changed in white adipose tissue and skeletal muscle from cold-exposed mice. Our results suggest that Glut 4 expression is differently modulated in the three insulin-responsive tissues during cold acclimation.     

Glucose transporter in insulin sensitive tissues of lean and obese mice. Effect of the thermogenic agent BRL 26830A

Glucose transport is decreased in skeletal muscle and adipose tissues of obese, hyperglycemic, insulin-resistant animals. Here we have characterized the glucose transporter(s) in muscle and adipose tissues from normal and obese mice, and we have studied the effect of a treatment with the thermogenic agent BRL 26830A. Glucose transporters were examined in crude tissue membrane fractions (microsomal + plasma membranes) by Western blot analysis using antipeptide antibodies specific for the erythroid (Glut 1) or muscle/fat (Glut 4) glucose transporters. In these insulin sensitive tissues, only Glut 4 was detected. In membranes from obese animals, the Glut 4 number was decreased by 40% +/- 4% in brown adipose tissue (mean +/- SEM of 9 preparations, P less than 0.001), whether the results were expressed per total tissue or per mg of protein. By contrast, Glut 4 number was unchanged in skeletal muscle. In white adipose tissue of obese animals, Glut 4 number per total fat pad was increased. However, due to the enlarged fat pad size, Glut 4 content was diminished when expressed per mg of white adipose tissue membrane protein in obese compared to lean animals. After a 18 day-treatment with BRL 26830A (1 or 2 mg/kg.day), glycemia of obese mice, which was slightly elevated compared to lean animals, was normalized, while insulinemia remained markedly above control values. In brown adipose tissue, the total number of Glut 4 returned to normal at 1 mg of the drug, or increased by 63% +/- 14% at 2 mg. Since membrane protein content was increased by the treatment, when results were expressed per mg of membrane protein, Glut 4 was similar in lean and BRL 26830A (1 or 2 mg) treated obese mice. BRL 26830A treatment did not modify Glut 4 in skeletal muscle, and it increased Glut 4 number in white adipose tissue in a dose-dependent manner. In conclusion, in obese mice, the glucose transporter number was reduced mainly in brown adipose tissue, a defect which could contribute to the hyperglycemic syndrome. Treatment with the thermogenic agent BRL 26830A normalized in parallel glycemia and glucose transporter number in brown adipose tissue, suggesting that this tissue could play a role in glucose homeostasis in rodents.     

高脂饲养及罗格列酮干预对大鼠胰岛素信号系统基因表达的影响

目的观察高脂饲养大鼠胰岛素信号转导系统基因表达的变化与外周组织葡萄糖代谢的关系及罗格列酮干预的效果。方法30只大鼠随机分为正常饲养（NC）组、高脂饲养（HF）组和HF＋罗格列酮（RGS）组。以静脉糖耐量试验血糖曲线下面积评价负荷后血糖处理能力;以3^H-2-脱氧葡萄糖（3^H-2-DG）摄取率评价肌肉和脂肪组织对葡萄糖的摄取能力;以RT-PCR方法分析肌肉和脂肪胰岛素受体、胰岛素受体底物1（IRS1）、IRS2和葡萄糖转运子4（GluT-4）mRNA表达的变化。结果与NC组比较,HF组GluAUC增加24.1%,肌肉和脂肪组织3^H-2-DG摄取率分别下降36.7%和48.1%;在所检测的基因中,仅肌肉和脂肪组织IRS1mRNA表达分别减少了64.8%和45.7%。与HF组比较,HF＋RGS组GluAUC降低了12.9%,肌肉和脂肪组织3^H-2-DG摄取率分别增加了66.3%和66.7%。结论高脂饲养造成IRS1表达下降,与外周组织葡萄糖摄取和利用减少相关;罗格列酮干预可使葡萄糖摄取和利用增加。     

Expression of insulin target genes in skeletal muscle and adipose tissue in adult patients with growth hormone deficiency: effect of one year recombinant human growth hormone therapy.

Our aim was to investigate the effects of one year recombinant human growth hormone (rhGH) therapy on the regulation by insulin of gene expression in muscle and adipose tissue in adults with secondary GH deficiency (GHD). Six GHD subjects without upper-body obesity were submitted to a 3-h euglycemic hyperinsulinemic clamp before and after one year of rhGH therapy. Muscle and abdominal subcutaneous adipose tissue biopsies were taken before and at the end of each clamp. The mRNA levels of insulin receptor, p85 alpha-phosphatidylinositol-3 kinase (p85 alpha PI-3K), insulin dependent glucose transporter (Glut4), hexokinase II, glycogen synthase, lipoprotein lipase (LPL) in muscle and in adipose tissue, hormone sensitive lipase and peroxisome proliferator-activated receptor gamma (PPAR gamma) in adipose tissue were quantified by RT-competitive PCR. One year treatment with rhGH (1.25 IU/day) increased plasma IGF-I concentrations (54+/-7 vs 154+/-11 ng/ml, P<0.01) but did not affect insulin-stimulated glucose disposal rate measured during the hyperinsulinemic clamp (74+/-9 vs 85+/-5 micromol/kg free fat mass/min). Insulin significantly increased p85 alpha PI-3K, hexokinase II and Glut4 mRNA levels in muscle both before and after rhGH treatment. One year of GH therapy increased LPL mRNA levels in muscle (38+/-2 vs 70+/-7 amol/microg total RNA, P<0.05) and in adipose tissue (2490+/-260 vs 4860+/-880 amol/microg total RNA, P<0.05), but did not change the expression of the other mRNAs. We conclude from this study that GH therapy did not alter whole body insulin sensitivity and the response of gene expression to insulin in skeletal muscle of adult GHD patients, but it did increase LPL expression in muscle and adipose tissue. This result could be related to the documented beneficial effect of GH therapy on lipid metabolism.     

Programming of rat muscle and fat metabolism by in utero overexposure to glucocorticoids

In utero overexposure to glucocorticoids may explain the association between low birth weight and subsequent development of the metabolic syndrome. We previously showed that prenatal dexamethasone (dex) exposure in the rat lowers birth weight and programs adult fasting and postprandial hyperglycemia, associated with increased hepatic gluconeogenesis driven by elevated liver glucocorticoid receptor (GR) expression. This study aimed to determine whether prenatal dex (100 microg/kg per day from embryonic d 15 to embryonic d 21) programs adult GR expression in skeletal muscle and/or adipose tissue and whether this contributes to altered peripheral glucose uptake or metabolism. In utero dex-exposed rats remained lighter until 6 months of age, despite some early catch-up growth. Adults had smaller epididymal fat pads, with a relative increase in muscle size. Although glycogen storage was reduced in quadriceps, 2-deoxyglucose uptake into extensor digitorum longus muscle was increased by 32% (P < 0.05), whereas uptake in other muscles and adipose beds was unaffected by prenatal dex. GR mRNA was not different in most muscles but selectively reduced in soleus (by 23%, P < 0.05). However, GR mRNA was markedly increased specifically in retroperitoneal fat (by 50%, P < 0.02). This was accompanied by a shift from peroxisomal proliferator-activated receptor gamma 1 to gamma 2 expression and a reduction in lipoprotein lipase mRNA (by 28%, P < 0.02). Adipose leptin, uncoupling protein-3 and resistin mRNAs, muscle GLUT-4, and circulating lipids were not affected by prenatal dex. These data suggest that hyperglycemia in 6-month-old rats exposed to dexamethasone in utero is not due to attenuated peripheral glucose disposal. However, increased GR and attenuated fatty acid uptake specifically in visceral adipose are consistent with insulin resistance in this crucial metabolic depot and could indirectly contribute to increased hepatic glucose output.     

Glucose uptake and perfusion in subcutaneous and visceral adipose tissue during insulin stimulation in nonobese and obese humans

To elucidate the role of adipose tissue glucose uptake in whole-body metabolism, sc and visceral adipose tissue glucose uptake and perfusion were measured in 10 nonobese and 10 age-matched obese men with positron emission tomography using [(18)F]-2-fluoro-2-deoxy-D-glucose, and [(15)O]-labeled water during normoglycemic hyperinsulinemia. Whole-body and skeletal muscle glucose uptake rates per kilogram were lower in obese than in nonobese subjects (P < 0.01). Compared with nonobese, the obese subjects had 67% lower abdominal sc and 58% lower visceral adipose tissue glucose uptake per kilogram of fat. In both groups, insulin stimulated glucose uptake per kilogram fat was significantly higher in visceral fat depots than in sc regions (P < 0.01). Both sc and visceral adipose tissue blood flow expressed per kilogram and minute was impaired in the obese subjects, compared with the nonobese (P < 0.05). Fat masses measured with magnetic resonance images were higher in obese than in nonobese individuals. If regional glucose uptake rates were expressed as per total fat mass, total glucose uptake rates per depot were similar in obese and nonobese subjects and represented 4.1% of whole-body glucose uptake in obese and 2.6% in nonobese subjects (P < 0.02 between the groups). In conclusion, insulin-stimulated glucose uptake per kilogram fat is higher in visceral than in sc adipose tissue. Glucose uptake and blood flow in adipose tissue exhibit insulin resistance in obesity, but because of the larger fat mass, adipose tissue does not seem to contribute substantially to the reduced insulin stimulated whole-body glucose uptake in obesity.     

Normal muscle glucose uptake in mice deficient in muscle GLUT4

Skeletal muscle insulin resistance is a major characteristic underpinning type 2 diabetes. Impairments in the insulin responsiveness of the glucose transporter, Glut4 (Slc2a4), have been suggested to be a contributing factor to this disturbance. We have produced muscle-specific Glut4 knockout (KO) mice using Cre/LoxP technology on a C57BL6/J background and shown undetectable levels of GLUT4 in both skeletal muscle and heart. Our aim was to determine whether complete deletion of muscle GLUT4 does in fact lead to perturbations in glucose homoeostasis. Glucose tolerance, glucose turnover and 2-deoxyglucose uptake into muscle and fat under basal and insulin-stimulated conditions were assessed in 12-week-old KO and control mice using the oral glucose tolerance test (OGTT) and hyperinsulinaemic/euglycaemic clamp respectively. KO mice weighed ～17% less and had significantly heavier hearts compared with control mice. Basally, plasma glucose and plasma insulin were significantly lower in the KO compared with control mice, which conferred normal glucose tolerance. Despite the lack of GLUT4 in the KO mouse muscle, glucose uptake was not impaired in skeletal muscle but was reduced in heart under insulin-stimulated conditions. Neither GLUT1 nor GLUT12 protein levels were altered in the skeletal muscle or heart tissue of our KO mice. High-fat feeding did not alter glucose tolerance in the KO mice but led to elevated plasma insulin levels during the glucose tolerance test. Our study demonstrates that deletion of muscle GLUT4 does not adversely affect glucose disposal and glucose tolerance and that compensation from other transporters may contribute to this unaltered homoeostasis of glucose.     

Involvement of bradykinin and nitric oxide in leptin-mediated glucose uptake in skeletal muscle

Regulation of glucose metabolism in peripheral tissues by leptin has been highlighted recently, although its mechanism is unclear. In this study, we postulated that bradykinin and nitric oxide (NO) are involved in the effect of leptin-mediated glucose uptake in peripheral tissues and examined these possibilities. Injection of leptin (200 pg/mouse) into the ventromedial hypothalamus-enhanced glucose uptake in skeletal muscle and brown adipose tissue, but not in white adipose tissue. Treatment with Hoe140 (0.1 mg/kg), bradykinin B2 receptor antagonist, or L-NAME (N:(G)-nitro-L-arginine methyl ester) (30 mg/kg), nitric oxide synthase inhibitor, did not influence the basal level of glucose uptake in skeletal muscle and the adipose tissue, whereas Hoe140 and L-NAME inhibited leptin-mediated glucose uptake in skeletal muscles, but had no effect in adipose tissue. However, Hoe140 and L-NAME did not inhibit insulin (1.0 U/kg)-mediated glucose uptake in all tissues examined. Taken together, these results suggest that leptin enhances bradykinin and/or the NO system, which contributes at least partially to the enhanced glucose uptake in skeletal muscles.