罗格列酮对糖尿病大鼠骨骼肌损害防护作用的机制研究

目的探讨罗格列酮对糖尿病大鼠骨骼肌损害防护作用的机制。方法用链脲佐菌素(STZ)将39只10周龄雄性Wistar大鼠诱导成糖尿病大鼠模型,分为胰岛素治疗组、罗格列酮治疗组、未治疗组(每组13只),并以13只正常大鼠作对照。于第16周末抽取各组大鼠心脏血测定TNF-α、IL-6、C-反应蛋白、SOD、P物质水平,并处死取股二头肌进行病理学观察;用免疫组织化学染色观察骨骼肌中晚期糖基化终末产物(AGEs)与过氧化物酶体增殖物激活受体(PPAR-γ)含量的变化。结果未治疗组血清IL-6、TNF-α、C-反应蛋白水平均明显高于正常组(P<0.05),胰岛素组和罗格列酮组则与正常对照组比较无差异;未治疗组血清SOD、SP水平与正常组相比明显降低(P<0.01),胰岛素组和罗格列酮组的SOD和P物质二者显著高于糖尿病组(P<0.01,P<0.05)。组织学观察:糖尿病组骨骼肌普遍萎缩,肌纤维横截面积明显缩小;部分肌纤维变性,间质水肿,炎细胞浸润;胰岛素组和罗格列酮组骨骼肌有部分轻度萎缩,间质轻度水肿,少量淋巴细胞浸润。免疫组织化学显示:AGEs蛋白、PPAR-γ蛋白均呈棕黄色颗粒状,弥漫或斑片状沉积于骨骼肌细胞胞浆中;在糖尿病组AGEs最高,PPAR-γ最低。结论糖尿病大鼠受损的骨骼肌中有AGEs蓄积和血清炎症因子增高,罗格列酮对糖尿病大鼠骨骼肌损害具有防护作用。     

罗格列酮对胰岛素抵抗大鼠骨骼肌蛋白激酶B表达的影响

目的 :探讨胰岛素增敏剂罗格列酮对胰岛素抵抗大鼠骨骼肌蛋白激酶B(PKB)表达的影响。方法 :应用高脂饲料喂养复制胰岛素抵抗大鼠模型。应用Westernblotting方法检测骨骼肌中PKB的表达。结果 :持续高脂饲料喂养组大鼠产生了明显胰岛素抵抗 ,骨骼肌PKB的表达较正常对照组显著降低 (OD值 8.2 4±s 0 .11vs 9.36± 0 .18,P <0 .0 1) ,罗格列酮治疗组和正常饲料替代组大鼠胰岛素抵抗明显改善 ,PKB的表达较持续高脂饲料喂养组大鼠明显增加 (OD值分别为 8.89± 0 .0 8,8.4 0± 0 .0 9vs 8.2 4± 0 .11,P <0 .0 1)。结论 :高脂喂养的大鼠胰岛素抵抗的产生与骨骼肌胰岛素刺激的PKB表达降低有明显关系 ,罗格列酮能显著增加已经降低了的胰岛素抵抗大鼠骨骼肌中PKB的表达 ,部分恢复受损的胰岛素信号转导 ,进而明显改善胰岛素抵抗 ,这可能也是罗格列酮减轻胰岛素抵抗的作用机制之一。     

Effects of the K+ channel opener KRN4884 on the cardiovascular metabolic syndrome model in rats

We examined the effects of the potassium channel opener KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine ) on cardiovascular metabolic syndrome (i.e., syndrome X), in rats. High-fructose diet rats developed hypertension, hypertriglyceridemia, increased total cholesterol/HDL (high-density lipoprotein)-cholesterol ratio, and hyperinsulinemia, KRN4884 (0.3-3.0 mg/kg, twice a day for 14 days, p.o.) alleviated the risk factors in fructose-fed rats. Furthermore, fructose-fed rats exhibited impairment of glucose tolerance and excess insulin secretion when loaded with glucose orally. Treatment with KRN4884 (1.0 mg/kg, twice a day for 14 days, p.o.) improved the glucose intolerance and inhibited hypersecretion of insulin in the glucose-loaded, fructose-fed rats. In contrast, KRN4884 (0.3-1.0 mg/kg, twice a day for 10 days, p.o.) did not affect serum triglyceride, cholesterol, glucose, or insulin concentrations in normal rats. LPL (lipoprotein lipase) activities in skeletal muscle and adipose tissue, and HTGL (hepatic triglyceride lipase) activity in liver were measured after administration of KRN4884 or vehicle twice a day for 14 days in fructose-fed rats. KRN4884 caused a significant increase in LPL activity in muscle and tended to increase LPL activity in adipose tissue in fructose-fed rats. HTGL was decreased in fructose-fed rats as compared with normal controls and was unaffected by KRN4884. These findings suggested that KRN4884 enhances insulin sensitivity and LPL activity, which are related to glucose and lipid metabolism and may be useful for the treatment of syndrome X.     

大鼠放射性脑损伤所致血脑屏障通透性改变与EBA 及 VEGF 表达的相关性研究

摘要： 目的 探究脑皮质内皮屏障抗原 （EBA） 及血管内皮生长因子 （VEGF） 在放射性血脑屏障损害条件下的动态变化规律, 为临床提供参考。方法 使用随机数字表法将 48 只清洁级雄性 SD 大鼠分为对照组和放射性脑损伤后 7、 14 和 28 d 4 组, 每组 12 只。采用 X 线电子计算机断层扫描设备制备大鼠放射性脑损伤模型。大鼠按照 3 mL/kg的剂量尾静脉注射 3%伊文思蓝 （EB）, 开颅并暴露脑皮质血管, 放于微循环显微镜下观察 EB 渗出情况, 并借助微循环显微成像系统评估血脑屏障通透性; 使用免疫组化染色的方法来检测各组大鼠脑皮质 EBA 和 VEGF 的表达。结果 与对照组相比, 损伤组大鼠脑皮质微血管 EB 外渗量和 VEGF 的表达水平于伤后 7、 14、 28 d 均有不同程度升高（均 P＜0.05）, 从伤后 7 d 至 28 d 逐渐降低, 损伤各亚组之间差异均有统计学意义（均 P＜0.05）, 二者呈正相关（r=0.898, P < 0.001）; EBA 表达水平于伤后各个时间点均下降 （均 P＜0.05）, 从伤后 7 d 至 28 d 逐渐升高, 损伤各亚组之间差异均有统计学意义 （均 P＜0.05）, 与 EB 外渗量呈负相关 （r=-0.866, P < 0.001）。结论 大鼠放射性脑损伤后血脑屏障通透性增加与 EBA 表达减少、 VEGF 表达增加具有重要关联性。     

Insulin unexpectedly increases the glucose 6-phosphate Ka of skeletal muscle glycogen synthase in calorie-restricted monkeys

In skeletal muscle of normal subjects, the concentration of glucose 6-phosphate (G6P) at which the activity of glycogen synthase (GS) is half maximal (Ka) is decreased by in vivo insulin, and the fractional activity is increased without a change in GS maximal activity (Vmax). We have shown that moderate chronic calorie restriction, previously shown in rodents to be effective in slowing aging, resulted in the prevention of obesity and type 2 diabetes in primates (rhesus monkeys, Macaca mulatta). However, unexpectedly, in a subgroup of calorie-restricted monkeys, insulin during a euglycemic hyperinsulinemic clamp caused an unanticipated decrease in skeletal muscle GS fractional activity. These same monkeys had the lowest whole-body glucose disposal rate (M), the greatest increase in skeletal muscle G6P content and the greatest increase in skeletal muscle glycogen phosphorylase activity during the euglycemic hyperinsulinemic clamp compared to the remaining calorie-restricted monkeys with normal insulin action. To determine whether this highly unusual insulin-mediated decrease in GS fractional activity was due to increased phosphorylation (increased Ka), we measured the activity of skeletal muscle GS at 9 different G6P concentrations before and during the euglycemic hyperinsulinemic clamp in 6 calorie-restricted monkeys. G6P Ka increased (n = 4) and Vmax decreased (n = 5) during the clamp. Basal G6P Ka was inversely related to basal GSfv (r = -0.94, p < 0.002). G6P Ka and skeletal muscle G6P content were positively related under insulin-stimulated conditions (r = 0.93, p < 0.005). The change in G6P Ka (insulin-stimulated minus basal) was inversely related to M (r = -0.94, p < 0.002) and positively related to the change in skeletal muscle G6P content (r = 0.93, p < 0.005). We conclude that moderate calorie restriction results in a reversal of normal insulin action at the skeletal muscle with inactivation of glycogen synthase which is likely to be due to an increase in phosphorylation of GS together with a decrease in Vmax of GS during a euglycemic hyperinsulinemic clamp in most of the calorie-restricted monkeys. These alterations are likely to be involved in the anti-diabetogenic effects of calorie restriction.     

Genistein modulates NF-κB-associated renal inflammation, fibrosis and podocyte abnormalities in fructose-fed rats

The study determines the effect of genistein on inflammatory status and expression of nuclear factor-kappa B (NF-κB p65), transforming growth factor-β1 (TGF-β1) and receptor for advanced glycation end products (RAGE) in kidney of fructose-fed rats. Adult male Wistar rats were fed a diet containing either starch or fructose as the source of carbohydrate. Fifteen days later, after confirming the development of insulin resistance in fructose-fed rats, the rats in each dietary group were divided into two and treated with either genistein (1 mg/kg/day) in 30% dimethylsulfoxide (DMSO) or 30% DMSO alone for the next 45 days. The expression of NF-κB P(65), TGF-β1 and RAGE, histochemical localization of α-smooth muscle actin (α-SMA), levels of tumour necrosis factor-α (TNF-α) and interleukin-6(IL-6) and ultrastructural analysis were performed at the end of the experimental period. Fructose-fed rats displayed inflammatory changes in kidney. Increased expression of TGF-β1 and RAGE in cytosol and NF-κB p65 in nuclear fraction were observed. α-SMA expression was higher in fructose-fed rat kidney. Proliferation of connective tissue was evident from increased collagen deposition in perivascular and intraglomerular regions. Administration of genistein to fructose-fed rats reduced inflammation, fibrogenesis and NF-κB activation. Genistein also mitigated the structural changes such as basement membrane thickening, reduction in podocyte number and loss of glomerular filtration barrier integrity. These findings suggest that genistein prevents inflammation, fibrosis and early nephropathic changes in fructose-fed insulin resistant rats secondary to the attenuation of NF-κB activation.     

Rosiglitazone ameliorates abnormal expression and activity of protein tyrosine phosphatase 1B in the skeletal muscle of fat-fed, streptozotocin-treated diabetic rats

Protein tyrosine phosphatase 1B (PTP1B) acts as a physiological negative regulator of insulin signaling by dephosphorylating the activated insulin receptor (IR). Here we examine the role of PTP1B in the insulin-sensitizing action of rosiglitazone (RSG) in skeletal muscle and liver. Fat-fed, streptozotocin-treated rats (10-week-old), an animal model of type II diabetes, and age-matched, nondiabetic controls were treated with RSG (10 micromol kg(-1) day(-1)) for 2 weeks. After RSG treatment, the diabetic rats showed a significant decrease in blood glucose and improved insulin sensitivity. Diabetic rats showed significantly increased levels and activities of PTP1B in the skeletal muscle (1.6- and 2-fold, respectively) and liver (1.7- and 1.8-fold, respectively), thus diminishing insulin signaling in the target tissues. We found that the decreases in insulin-stimulated glucose uptake (55%), tyrosine phosphorylation of IRbeta-subunits (48%), and IR substrate-1 (IRS-1) (39%) in muscles of diabetic rats were normalized after RSG treatment. These effects were associated with 34 and 30% decreases in increased PTP1B levels and activities, respectively, in skeletal muscles of diabetic rats. In contrast, RSG did not affect the increased PTP1B levels and activities or the already reduced insulin-stimulated glycogen synthesis and tyrosine phosphorylation of IRbeta-subunits and IRS-2 in livers of diabetic rats. RSG treatment in normal rats did not significantly change PTP1B activities and levels or protein levels of IRbeta, IRS-1, and -2 in diabetic rats. These data suggest that RSG enhances insulin activity in skeletal muscle of diabetic rats possibly by ameliorating abnormal levels and activities of PTP1B.     

Rosiglitazone decreases plasma levels of osteoprotegerin in a randomized clinical trial with type 2 diabetes patients

Cardiovascular disease is the leading cause of death in patients with type 2 diabetes mellitus (T2DM). We suggested that plasma osteoprotegerin (OPG), a strong, independent predictor of cardiovascular disease, could discriminate between anti-diabetic treatments depending on their benefits regarding cardiovascular disease. The South Danish Diabetes Study, an investigator-driven, randomized, controlled clinical trial lasting 2 years, was used to test this hypothesis in patient groups with different medication strategies (insulin aspart or NPH insulin, added either metformin/placebo or rosiglitazone/placebo). A total of 371 individuals were eligible for the study. Basic variables were analysed along with measurement of plasma OPG and HbA(1c) at the beginning and end of the study. Only rosiglitazone treatment caused a significant decrease in plasma OPG concentrations (p = 0.003), while no significant change was seen in the other treatment groups. The effect of rosiglitazone on plasma OPG remained significant in a univariate analysis adjusted for change in HbA(1c) (p = 0.013). Of note, the change in plasma OPG significantly correlated with HbA(1c) improvement in rosiglitazone-treated patients (R = 0.29, p = 0.0002), while this correlation was poor in those not receiving rosiglitazone (R = 0.06, p =0.48). Treatment with rosiglitazone among patients with T2DM reduces the concentration of plasma OPG. This is not seen with metformin despite similar reductions in HbA(1c) . Alteration in the OPG/RANKL pathway by glitazones may have implications for the understanding of both cardiovascular effects and bone side effects of the drug.     

罗格列酮的胰岛素增敏作用和胰岛素抵抗改善作用

目的　观察罗格列酮的胰岛素增敏作用和胰岛素抵抗改善作用。方法　大鼠尾静脉注射链佐菌素 (5 0mg·kg-1)制备IDDM模型 ,观察单用罗格列酮、单用小剂量胰岛素 (皮下注射 2 5U·鼠 -1)、罗格列酮并用小剂量胰岛素的降糖作用 ;大鼠尾静脉注射卡介苗 (10mg·鼠 -1)制备免疫性胰岛素抵抗模型 ,观察罗格列酮对模型的葡萄糖输注速率的回升作用。结果　罗格列酮 1,3 ,10 μmol·kg-13个剂量组连续灌胃给药 8d ,均未能降低正常大鼠血糖 ,也未能降低链佐菌素所致糖尿病大鼠血糖 ;但在并用小剂量胰岛素条件下 ,罗格列酮 3 ,10 μmol·kg-1连续灌胃给药 8d ,能降低链佐菌素所致糖尿病大鼠血糖 ;罗格列酮 10 μmol·kg-1连续灌胃给药 8d后 ,用正糖钳技术检测 ,免疫性胰岛素抵抗模型亚极高和极高胰岛素状态下的葡萄糖输注速率均得到回升。结论　罗格列酮具有胰岛素增敏作用和胰岛素抵抗改善作用     

Beta2‐adrenergic agonist clenbuterol increases energy expenditure and fat oxidation,and induces mTOR phosphorylation in skeletal muscle of young healthy men

Clenbuterol is a beta₂‐adrenoceptor agonist marketed as an asthma reliever but is not approved for human use in most countries due to concerns of adverse cardiac effects. Given its demonstrated hypertrophic and lipolytic actions in rodents, clenbuterol is one of the most widely abused doping substances amongt athletes and recreational body‐builders seeking leanness. Herein, we examined the effect of clenbuterol ingestion on metabolic rate as well as skeletal muscle mammalian target of rapamycin (mTOR) phosphorylation and protein kinase A (PKA)‐signaling in six young men. Before and 140 min after ingestion of 80 μg clenbuterol, resting metabolic rate and contractile function of the quadriceps muscle were measured, and blood samples as well as vastus lateralis muscle biopsies were collected. Clenbuterol increased resting energy expenditure by 21% (P < 0.001), and fat oxidation by 39% (P = 0.006), whereas carbohydrate oxidation was unchanged. Phosphorylation of mTOR^Ser2448 and PKA substrates increased by 121% (P = 0.004) and 35% (P = 0.006), respectively, with clenbuterol. Maximal voluntary contraction torque decreased by 4% (P = 0.026) and the half‐relaxation time shortened by 9% (P = 0.046), while voluntary activation, time to peak twitch, and peak twitch torque did not change significantly with clenbuterol. Glycogen content of the vastus lateralis muscle did not change with clenbuterol. Clenbuterol increased circulating levels of glucose (+30%; P < 0.001), lactate (+90%; P = 0.004), insulin (+130%; P = 0.009), and fatty acids (+180%; P = 0.001). Collectively, these findings indicate that clenbuterol is an efficient thermogenic substance that possibly also exerts muscle hypertrophic actions in humans. For these reasons, the restrictions imposed against clenbuterol in competitive sports seem warranted.     

小檗碱对2型糖尿病大鼠骨骼肌糖脂代谢的影响及其机制

目的观察小檗碱对糖尿病大鼠骨骼肌病理结构改变和糖脂代谢紊乱的影响及其与PPARe α/γ/δ蛋白表达的关系。方法注射链脲菌素（35mg·kg^-1，i．p．）加高糖高脂饲料喂养16周建立2型糖尿病大鼠模型，随后16周每天分别拌食给予低中高剂量小檗碱（75、150、300mg·kg^-1）、非诺贝特（100mg·k^-1）和罗格列酮（4mg·k^-1），用HE染色检查骨骼肌结构病变、分光光度法测定肌糖元和甘油三脂含量及免疫组化检测PPAR α/γ/δ的表达。结果骨骼肌纤维在各组大鼠中仍正常分布，中高剂量小檗碱部分地改善糖尿病肌纤维的萎缩，增加肌糖元和降低甘油三脂含量（P〈0．01）。中高剂量小檗碱和罗格列酮都能明显降低糖尿病大鼠骨骼肌中PPARγ蛋白水平（P〈0．01），中高剂量小檗碱和非诺贝特能促进PPARα和PPARδ的表达（P〈0．01）。结论小檗碱调控骨骼肌PPARα/γ/δ蛋白的表达可能是其改善糖尿病骨骼肌纤维萎缩和糖脂代谢紊乱的机制之一。     

Skeletal muscle digoxin concentration during digitalization and during withdrawal of digoxin treatment

Summary Blood samples and skeletal muscle biopsies (m. quadriceps femoris, vastus lateralis) were taken from 15 patients during digitalization or during withdrawal of digoxin treatment for analysis of serum and skeletal muscle digoxin concentrations. A percutaneous needle biopsy technique was used for muscle sampling and digoxin was analysed by radio-immunoassay. During slow digitalization with 0.25 mg digoxin daily the skeletal muscle digoxin concentrations after 2 and 4 days were 45% (range 19%–62%; n=3) and 78% (range 56%–92%; n=3) respectively, of the steady state concentration (defined as the digoxin concentration after 25–40 days of treatment). After 9 and 11 days of treatment the skeletal muscle digoxin concentrations were 106% (range 84%–133%; n=5) and 116% (range 72%–164%; n=3) respectively, of the steady state concentration. A doubling of the digoxin dose gave a proportional increase in skeletal muscle digoxin concentration (three patients). The magnitude of the estimated half-life of skeletal muscle digoxin was the same as previously reported in healthy subjects. No significant correlations were found between changes in systolic time intervals and steady state serum or skeletal muscle digoxin concentrations.     

METABOLIC EFFECTS OF THIOCTIC ACID IN RODENT MODELS OF INSULIN RESISTANCE AND DIABETES

1. The antioxidant thioctic acid (TA) has been used in the treatment of diabetic neuropathy and recent studies have suggested that TA also has pancreatic and peripheral effects that improve glucose transport and metabolism. In the present study, the metabolic effects of TA were evaluated in rodent models of insulin resistance (fructose-fed Sprague-Dawley rat) and insulin deficiency (streptozotocin (STZ)-induced diabetic rat). Oral and intravenous glucose tolerance tests (OGTT and IVGTT, respectively) were performed in conscious rats after treatment with 50 mg/kg per day TA or vehicle for 5 days. 2. Fructose feeding for 7 days induced insulin resistance and impaired glucose tolerance and hypertriglycerideaemia. Treatment of fructose-fed rats with TA had no significant effect on fasting or stimulated glucose levels or on fasting triglyceride concentrations (e.g. the area under the curve for glucose (AUC_glu) following OGTT was 1233 ± 67 and 1284 ± 59 in fructose-fed rats treated with either TA (n= 12) or vehicle (n= 12), respectively). Similarly, TA had no significant effect on IVGTT profiles in fructose-induced insulin resistance. 3. Low-dose STZ (80 mg/kg, i.p, over 2 days) induced hyper-glycaemia, but TA had no significant glucose-lowering effects in STZ-diabetic rats (AUC_glu (OGTT) following oral administration was 5507 ± 27 and 5450 ± 27 in TA (n= 12) and vehicle-treated (n= 12) rats, respectively). Nor did pretreatment with TA affect the diabetogenic response to STZ. 4. In contrast with previous in vitro studies reporting favourable metabolic effects of TA, the present study shows that after short-term oral therapy there are no significant improvements in glucose tolerance in rodent models of insulin resistance and insulin deficiency. Thioctic acid is unlikely to be of therapeutic benefit as an anti-diabetic drug in clinical practice.     

急性冠状动脉综合征患者胰岛素抵抗与血管内皮功能关系的研究

目的 探讨急性冠状动脉综合征（ACS）患者胰岛素抵抗与血管内皮功能的关系。方法 选择96例ACS患者，通过测定空腹血糖（FBG）及胰岛素水平（FSI），计算其胰岛素抵抗指数（IR），据此将之分为胰岛素敏感组和胰岛素抵抗组，分别于第4、8、12周测定FBG、FSI、一氧化氮（NO）、血管内皮生长因子（VEGF）和肱动脉血流介导的内皮依赖性舒张功能（EDD）。结果 IR与NO、EDD呈负相关（r=-0．451、P=0．000，r=-0．280、P=0．006）；IR与VEGF呈正相关（r=0．614，P=0．000）；NO与EDD呈正相关（r=0．228，P=0．026），NO与VEGF呈负相关（r=-0．385，P=0．000）；VEGF与EDD呈负相关（r=-0．263，P=0．010）。结论 急性冠状动脉综合征患者血浆胰岛素抵抗与血管内皮功能及VEGF水平关系密切。     

Metabolic effects of benzylidene thiazolidinedione derivatives in high-fat fed mice

Thiazolidinediones are insulin-sensitizing agents that working by binding to PPAR-γ, which leads to alteration in the expression of key regulators of lipid homeostasis, glucoregulatory, and insulin resistance genes. In this study, we investigated the effects of treatment with the benzylidene thiazolidinedione (BTZD) derivatives; (5Z)-5-(4-chloro-benzylidene)-3-(4-methyl-benzyl)-thiazolidine-2,4-dione (1), (5Z)-5-(4-methoxy-benzylidene)-3-(4-methyl-benzyl)-thiazolidine-2,4-dione (2), (5Z)-5-(2,4-dimethoxy-benzylidene)-3-(4-methyl-benzyl)-thiazolidine-2,4-dione (3), and (5Z)-5-(4-dimethylamino-benzylidene)-3-(4-methyl-benzyl)-thiazolidine-2,4-dione (4) on insulin resistance associated with hyperinsulinemia, hyperglycemia, and hyperlipidemia in high-fat diet induced mice. Body weight, serum triglyceride and total cholesterol, aspartate aminotransferase (AST), alanine aminotransferase (ALT), fasting serum glucose (FSG), and fasting serum insulin levels (FSI) of all groups were assayed. The insulin resistance indices were calculated using the homeostasis model assessment (HOMA-IR). None of the treatments caused any significant alteration in body weight. The elevated serum triglyceride, total cholesterol, FSG and FSI levels were reduced significantly (P?<?0.01) by BTZDs and rosiglitazone, in comparison with the control (HFD-C) group. Compound (2) was 34% more potent than rosiglitazone in terms of decreasing insulin levels (P?<?0.05). HOMA-IR indices of BTZDs and rosiglitazone-treated groups were significantly (P?<?0.01) improved when compared to the HFD-C group. Moreover, only the derivatives (1) and (2), were able to reduce the serum AST levels when compared with the HFD-C group. This study suggests that these BTZDs derivatives not only reduce insulin resistance in high-fat fed mice, but also ameliorate associated hyperinsulinemia, hyperglycemia, and hyperlipidemia. Additionally, none of the derivatives exerted any major adverse effect on liver transaminases or body weight.     

非诺贝特和罗格列酮对大鼠血脂、体重和胰岛素敏感性的作用比较

目的 :比较非诺贝特、罗格列酮对大鼠胰岛素敏感性、血脂、体重的影响。方法 :32只大鼠随机分为 4组 ,1组给予普通饲料 ,其余 3组给予高脂饲料喂养 ,制作胰岛素抵抗模型。 4wk后取高脂饲料喂养的 2组大鼠予非诺贝特 (10 0mg·kg- 1·d- 1)、罗格列酮 (8mg·kg- 1·d- 1)灌胃 ,其他 2组予安慰剂灌胃。结果 :给高脂饲料的 3组大鼠体重、血脂和胰岛素水平均明显增高 (P <0 .0 1)。给药后 ,非诺贝特组和罗格列酮组大鼠游离脂肪酸均降低 ,非诺贝特组血清三酰甘油降低 ,与高脂对照组对比差异有显著意义 [(0 .84±s0 .18)mmol·L- 1vs (1.2±0 .3)mmol·L- 1,P <0 .0 5 ]。非诺贝特组体重增长幅度减小 ,罗格列酮组体重增长幅度增加。 2种药物都能增加葡萄糖输注率 ,罗格列酮作用优于非诺贝特。结论 :非诺贝特可降低大鼠血脂、减少体重、有适度的胰岛素增敏作用。罗格列酮具有良好增敏作用及适度的降脂作用 ,可引起体重增加     

Differential effects of rexinoids and thiazolidinediones on metabolic gene expression in diabetic rodents

Both retinoid X receptor (RXR)-selective agonists (rexinoids) and thiazolidinediones (TZDs), PPAR (peroxisome proliferator-activated receptor)-gamma-specific ligands, produce insulin sensitization in diabetic rodents. In vitro studies have demonstrated that TZDs mediate their effects via the RXR/PPAR-gamma complex. To determine whether rexinoids lower hyperglycemia by activating the RXR/PPAR-gamma heterodimer in vivo, we compared the effects of a rexinoid (LG100268) and a TZD (rosiglitazone) on gene expression in white adipose tissue, skeletal muscle, and liver of Zucker diabetic fatty rats (ZDFs). In adipose tissue, rosiglitazone decreased tumor necrosis factor-alpha (TNF-alpha) mRNA and induced glucose transporter 4 (GLUT4), muscle carnitine palmitoyl-transferase (MCPT), stearoyl CoA desaturase (SCD1), and fatty acid translocase (CD36). In contrast, LG100268 increased TNF-alpha and had no effect or suppressed the expression of GLUT4, MCPT, SCD1, and CD36. In liver, the rexinoid increased MCPT, SCD1, and CD36 mRNAs, whereas rosiglitazone induced only a small increase in CD36. In skeletal muscle, rosiglitazone and LG100268 have similar effects; both increased SCD1 and CD36 mRNAs. The differences in the pattern of genes induced by the rexinoids and the TZDs in diabetic animals found in these studies suggests that these compounds may have independent and tissue-specific effects on metabolic control in vivo.     

Mechanism of suppression of insulin signalling with lignocaine

Lignocaine suppresses insulin-stimulated glucose transport into the cells and insulin-stimulated glycogenesis at doses equivalent to that used in the treatment of muscle pain disorder. We evaluated the direct effect of lignocaine on insulin receptor (IR) kinase activity. After lignocaine (40 mM, approximately equivalent to 1%) or an equal volume (100 microl) saline had been injected into the tibialis anterior muscle of rat, insulin (50 mM g-1 body weight) was administered into the portal vein in vivo. Immunoprecipitation and immunoblotting were used to detect insulin-mediated tyrosine phosphorylation of both IR-beta and insulin receptor substrate (IRS)-1, and insulin-stimulated binding of IRS-1 to p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3-K) in the extracted muscle. In the in vitro study, purified IR from rat liver and/or recombinant IRS-1 protein with adenosine triphosphate were incubated with lignocaine (4 or 40 mM). Lignocaine reduced insulin-stimulated tyrosine phosphorylation of IR-beta to 12.6+/-5.7% (P<0.001), and IRS-1 to 32.1+/-18.8% (P<0.01), and also reduced insulin-stimulated binding of IRS-1 to p85 to 27.4+/-12.7% (P<0.001) relative to control (100%) in muscle in vivo. The in vitro study revealed that lignocaine directly inhibited both basal and insulin-stimulated tyrosine phosphorylation of IR. These results indicate that clinically used doses of lignocaine inhibit insulin signalling in skeletal muscle. The inhibitory effect of lignocaine on tyrosine kinase activity of the IR underlies the suppression of insulin signalling with lignocaine.     

Hypoglycemic properties of taurine: Not mediated by enhanced insulin release

Taurine (2-aminoethanesulfonic acid) has been shown to be a potent hypoglycemie agent in the Wistar Kyoto rat (WKY). Glucose and insulin levels were measured in serum at various times after glucose loading (400 mg/kg, i.p.). Pretreatment with taurine (200 mg/kg, i.p.) attenuated the rise in serum glucose levels at 0.5 hr after glucose administration. In addition, taurine also prevented the rise in serum immunoreactive insulin levels. The taurine analogue hypotaurine produced a similar inhibition in the rise of both serum glucose and insulin levels while β-alanine, the car?ylic acid derivative of taurine, was totally ineffective. The enhanced glucose clearance can be explained by an increase in deoxyglucose accumulation in skeletal muscle and liver. In the liver, a 50% increase in glycogen synthesis was observed. A possible interrelationship between taurine and insulin receptor is discussed.     

Rosiglitazone increases cell surface GLUT4 levels in 3T3-L1 adipocytes through an enhancement of endosomal recycling

Insulin induces a translocation of the glucose transporter GLUT4 from intracellular storage compartments towards the cell surface in adipocytes and skeletal muscle cells, allowing the cells to take up glucose. In type 2 diabetes-associated insulin resistance, the efficiency of this process is reduced. The thiazolidinediones, widely prescribed as anti-diabetic therapy, are generally regarded as insulin-sensitizers. The aim of this study was to evaluate the effect of the thiazolidinedione rosiglitazone (BRL 49653) on GLUT4 in adipocytes. When applied during differentiation, rosiglitazone dose dependently augmented GLUT4 expression along with the formation of lipid droplets. Intriguingly, its presence during differentiation led to increases in both cell surface GLUT4 levels and insulin sensitivity of GLUT4 translocation in mature adipocytes. Treatment of fully differentiated adipocytes with rosiglitazone also led to increases in GLUT4 at the plasma membrane. Rosiglitazone similarly affected cell surface levels of the endosomal transferrin receptor, but did not alter the GLUT4 internalization rate. The augmentation in cell surface GLUT4 levels was maintained in adipocytes that were rendered insulin-resistant in vitro by a 24 h insulin treatment and moreover in these cells rosiglitazone also fully restored insulin-induced GLUT4 translocation. We conclude that in adipocytes, rosiglitazone increases cell surface GLUT4 levels by increasing its endosomal recycling and restores insulin-induced GLUT4 translocation in insulin resistance. These results implicate novel modes of action on GLUT4 that are all likely to contribute to the insulin-sensitizing effect of rosiglitazone in type 2 diabetes.