Failure of dietary quercetin to alter the temporal progression of insulin resistance among tissues of C57BL/6J mice during the development of diet-induced obesity

Aims/hypotheses  High-fat diets produce obesity and glucose intolerance by promoting the development of insulin resistance in peripheral tissues and liver. The present studies sought to identify the initial site(s) where insulin resistance develops using a moderately high-fat diet and to assess whether the bioflavonoid, quercetin, ameliorates progression of this sequence. Methods  Four cohorts of male C57BL/6J mice were placed on diets formulated to be low-fat (10% of energy from fat), high-fat (45% of energy from fat) or high-fat plus 1.2% quercetin (wt/wt). After 3 and 8 weeks, cohorts were evaluated using euglycaemic–hyperinsulinaemic clamps, metabolomic analysis of fatty acylcarnitines and acute in vitro assessments of insulin signalling among tissues. Results  After 3 and 8 weeks, the high-fat diet produced whole-body insulin resistance without altering insulin-dependent glucose uptake in peripheral tissues. The primary defect was impaired suppression of hepatic glucose production by insulin at both times. Quercetin initially exacerbated the effect of high-fat diet by further increasing hepatic insulin resistance, but by 8 weeks insulin resistance and hepatic responsiveness to insulin were similarly compromised in both high-fat groups. The high-fat diet, irrespective of quercetin, increased short-chain fatty acylcarnitines in liver but not in muscle, while reciprocally reducing hepatic long-chain fatty acylcarnitines and increasing them in muscle. Conclusions/interpretation  Failure of insulin to suppress hepatic glucose output is the initial defect that accounts for the insulin resistance that develops after short-term consumption of a high-fat (45% of energy) diet. Hepatic insulin resistance is associated with accumulation of short- and medium-, but not long-chain fatty acylcarnitines. Dietary quercetin does not ameliorate the progression of this sequence. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Short-term regulation of insulin-mediated glucose utilization in four-day fasted human volunteers: role of amino acid availability

Summary Glucose homeostasis in men fasted for 84 h was assessed using isotopes, indirect calorimetry and forearm balance techniques during a basal period and three sequential hyperinsulinaemic euglycaemic clamps each lasting for 150 min. Two protocols (n=12 in each) were used: subjects were either allowed to develop hypoaminoacidaemia or received a commercial solution of L-amino acids while maintaining near-basal plasma leucine levels. Insulin infusions resulted in 3-, 35- and 650-fold increases in plasma insulin levels in both protocols. The infusion of amino acids produced a rightward shift in the dose-response curve of insulin's effect on suppressing hepatic glucose production, indicating decreased sensitivity in addition to blunting of the maximal responsiveness. Total body glucose rate of disappearance was progressively increased with escalating insulin doses, but was 22% lower at the intermediate and highest insulin doses in the group that was infused with amino acids (3.44±0.53 vs 4.82±0.71 and 7.72±1.01 vs 10.36±1.08 mg·kg^–1·min^–1, respectively; p<0.05). Forearm balance data confirmed the isotopic data, since amino acid infusions blunted the insulin-mediated increase in net forearm glucose utilization (by 50–83%). Furthermore, the infusion of amino acids resulted in marked reductions in the rate of carbohydrate oxidation and storage as assessed by indirect calorimetry. The data indicate that the amino acid-mediated suppression of glucose utilization and carbohydrate oxidation is exerted on the responsive component of insulin action.     

Comparative evaluation of simple insulin sensitivity methods based on the oral glucose tolerance test

Aims/hypothesis We compared five surrogate insulin sensitivity (IS) methods against the euglycaemic–hyperinsulinaemic clamp. These methods were the homeostasis model assessment (HOMA) and four methods based on the OGTT (OGIS, MCRest, ISIcomp, SIORAL).Methods We compared these IS methods against the clamp (0.28 nmol·min^–1·m^–2 insulin infusion) M value in 147 women (58–61 years; BMI 19–38 kg/m²; 116 NGT, 25 IFG/IGT, six type 2 diabetic), by evaluating the correlation coefficient with M. We also tested the ability to reproduce the relationships between IS and typical IS correlates (BMI, fasting insulin, insulin to glucose OGTT area ratio and fasting, 2 h and mean glucose) by means of the discrepancy index D, in which (1) D=0 if the correlation between IS and the variable of interest is as with the clamp, (2) D is smaller than 0 if the correlation is overestimated, and (3) D is greater than 0 if underestimated.Results All IS methods correlated with M (r=0.57–0.83, p<0.0001); for MCRest the relationship was markedly curvilinear. All IS measures correlated with the considered variables (r=0.29–0.94, p<0.0005); however, no method had D0 for all variables. The best surrogates of M were OGIS (one D0) and MCRest (two D0); the other methods either under- or overestimated the degree of correlation (three or more D0), in particular with fasting insulin (HOMA: D=–57%; ISIcomp: D=–36%) and BMI (HOMA: D=–14%; ISIcomp: D=–14%; SiORAL: D=–11%).Conclusions/interpretation All IS methods were correlated with M. OGIS and MCRest were preferable to the other methods and in particular to HOMA for reproducing relationships with the independent variables.     

A simple method for quantitation of insulin sensitivity and insulin release from an intravenous glucose tolerance test.

Both insulin secretion and insulin sensitivity are important in the development of diabetes but current methods used for their measurements are complex and cannot be used for epidemiological surveys. This study describes a simplified approach for the estimation of first phase insulin release and insulin sensitivity from a standard 40-min intravenous glucose tolerance test (IVGTT), and compares these parameter estimations with the sophisticated minimal model analysis of a frequently sampled 3-h IVGTT and the euglycaemic clamp technique. For the simplified IVGTT, first phase insulin release was measured as the insulin area above basal post glucose load unit-1 incremental change (i.e. peak rise) in plasma glucose over 0-10 min, and insulin sensitivity as a rate of glucose disappearance (Kg) unit-1 insulin increase above basal from 0-40 min post-glucose load in 18 subjects who were studied twice, either basally or in a perturbed pathophysiological state (i.e. pre- and post-ultramarathon race, n = 5; pre- and post-20 h pulsatile hyperinsulinaemia, n = 8; pre- and post-thyrotoxic state, n = 5). A further 12 subjects were compared by IVGTT, and glucose clamp. In addition, seven dogs were studied three times by IVGTT during normal saline infusion and after short-term (1/2 hour) or long-term (72 hour) adrenaline infusions. First phase insulin release and insulin sensitivity estimated from the simplified IVGTT as calculated by the two methods correlated closely (rs = 0.89 and rs = 0.87, respectively), although less precisely in markedly insulin-resistant subjects and the slopes and y intercepts of the linear regression lines were similar in the basal and perturbed states.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glycogen synthase kinase 3 inhibition improves insulin-stimulated glucose metabolism but not hypertension in high-fat-fed C57BL/6J mice

Aims/hypothesis In the current study, the effect of a highly specific peptide inhibitor of glycogen synthase kinase 3 (GSK3) (L803-mts) on glucose metabolism and BP was examined in a high-fat (HF) fed mouse model of diabetes. Methods C57/BL6J mice were placed on an HF diet for 3 months and treated with L803-mts for 20 days, following which glucose metabolism was examined by euglycaemic–hyperinsulinaemic clamp studies. BP and heart rate were measured by radio-telemetry. Results The HF mice were obese, with impaired glucose tolerance and high plasma insulin and leptin levels. L803-mts treatment significantly reduced the insulin levels and doubled the glucose infusion rate required to maintain a euglycaemic condition in the HF+L803-mts group compared with the HF group. Insulin failed to suppress the endogenous glucose production rate in the HF group while decreasing it by 75% in the HF+L803-mts group, accompanied by increased liver glycogen synthase activity and net hepatic glycogen synthesis. GSK3 inhibition also reduced peripheral insulin resistance. Plasma glucose disappearance rate increased by 60% in the HF+L803-mts group compared with the HF group. In addition, glucose uptake in heart and gastrocnemius muscle was markedly improved. Although mean arterial pressure increased following the HF diet, it did not change significantly during the 12 days of L803-mts treatment. Conclusions/interpretation These studies demonstrate that GSK3 inhibition improved hepatic and peripheral insulin resistance in a mouse model of HF-induced diabetes, but it failed to have an effect on BP. GSK3 may represent an important therapeutic target for insulin resistance.     

Study of the rate of early glucose disappearance following insulin injection: insulin sensitivity index

The euglycaemic hyperinsulinaemic glucose clamp is usually considered as the reference technique to evaluate insulin sensitivity. As it is an-expensive and time-consuming tool, we therefore tried to validate a simple insulin tolerance test (ITT) (IV bolus of 0.1 IU/kg of regular insulin, with glucose sampling at −5, 0, 3, 5, 7, 10 and 15 min) and to demonstrate its usefulness. Insulin sensitivity was measured by DG/G0 ratio (G0 = initial glycaemia, DG is the variation between G0 and the glycaemia obtained at 15 min by the calculation of the regression plot). We confirmed the existence of a correlation between the glucose uptake (mg/kg per min) evaluated by glucose clamp and the DG/G0 index (r = 0.9, P < 0.01). There was no stimulation of hormonal counter regulation during the test. The ITT was significantly correlated both with fasting insulin (r = −0.43, P < 0.01), and post-glucose load insulin concentration (r = −0.67, P < 0.01); each measurement expressing insulin sensitivity. Four groups of patients with different insulin sensitivity; controls, NIDDM, gynoid and android obese subjects, were clearly separated by ITT. We showed that fasting glycaemia and DG/G0 were correlated (y = 2.63/x − 0.093; r = 0.82, P < 0.01). These results suggest that ITT could be an easy, quick and low cost method to evaluate insulin resistance in clinical practice and epidemiological studies.     

糖调节受损不同亚型胰岛素敏感性和胰岛素分泌的特点

糖调节受损包括单纯空腹血糖受损、单纯糖耐量受损和混合糖调节受损三个亚型.流行病学资料及病理生理研究提示各个亚型具有不同的胰岛素分泌和胰岛素敏感性特点.了解这些特点有助于早期干预以阻止或延缓糖调节受损向2型糖尿病发展的进程.     

Some peculiarities of the glucoregulatory response to glucose infusion in the rat

Summary The glucoregulatory response to the i.v. infusion of different doses of glucose and glucose plus insulin was studied in anesthetized rats by using the primed constant infusion of glucose-2-³H. Infusion of glucose at the rate of 10 mg/kg/min induced a rise of about 100% in blood glucose, while the hepatic release of glucose showed only a small and transient decrease. A proportional increase of glycemia and glucose utilization (Rd) was observed without any appreciable change in the metabolic clearance rate (MCR) of glucose; a two-fold increase in plasma insulin was recorded at all times. In the group of rats receiving 20 mg/kg/min of glucose, changes in the above parameters were slightly greater; MCR showed a moderate increment in spite of the six-fold rise of plasma insulin. Finally, the infusion of large doses of insulin together with 20 mg/kg/min of glucose resulted in complete cessation of glucose release by the liver and in a remarkable increase of Rd and MCR. These results suggest a poor adaptability of the glucoregulatory system of the rat in response to glucose infusion as compared to other mammalian species.     

Surrogate index for insulin sensitivity composed of factors not using glucose and insulin in Japanese patients with diabetes

Introduction: The aim of the present study is to propose a novel index of insulin sensitivity instead of homeostasis model assessment of insulin resistance (HOMA‐IR), which has a fundamental limitation of validity when applied to subjects with lower insulin secretions or high fasting plasma glucose (FPG) levels. Materials and Methods: A total of 25 apparently healthy subjects and 24 patients with type 2 diabetes participated in the study. We assessed relationships of glucose infusion rate (GIR), obtained by using the euglycemic hyperinsulinemic glucose clamp technique, with other measurements of metabolic and anthropometric parameters. Results: In multiple regression analysis, a model including log‐transformed (log) triglyceride/log high‐density lipoprotein cholesterol and waist circumference as predictive variables showed the strongest contribution rate to explain GIR as an outcome variable (R² = 0.710). The validity of estimated GIR (EGIR) calculated from the regression equation composed of these factors was further tested in another group of patients including type 1, type 2 and pancreatic diabetes in whom HOMA‐IR could not be used as a result of either high FPG or low fasting insulin level, or both. Even in those patients, EGIR showed a good positive relationship with measured GIR (r = 0.681, P < 0.0001). Conclusions: The proposed index without HOMA‐IR can adequately show insulin sensitivity in Japanese diabetic patients, even in cases with the limitation of HOMA‐IR application. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00076.x , 2010)     

Insulin supplement in type 2 diabetic patients with secondary failure to oral agents ameliorates hepatic and peripheral insulin sensitivity but not insulin secretion

In order to investigate the mechanism of amelioration of metabolic abnormalities with supplementary doses of insulin, islet B-cell function and insulin sensitivity were measured in 10 patients with Type 2 diabetes in secondary failure to oral agents. A small dose of ultralente insulin (0.26 +/- 0.07 U kg-ideal-body-weight-1) was added in the morning before breakfast. After 3 months insulin therapy and progressive improvement of metabolic control (HbA1 from 10.5 +/- 0.4 to 9.0 +/- 0.3% at the end of insulin treatment, p less than 0.001), basal C-peptide and incremental area during an oral glucose tolerance test were unchanged. In vivo peripheral insulin sensitivity (euglycaemic clamp with insulin infusion of 40, 160, and 600 mU m-2 min-1, respectively) was significantly improved (glucose requirement: to 4.7 +/- 1.0 from 3.0 +/- 0.6 mg kg-1 min-1, p less than 0.05 at first insulin level; to 10.8 +/- 0.5 from 9.3 +/- 0.7 mg kg-1 min-1, p less than 0.01 at second level; to 13.3 +/- 0.6 from 11.8 +/- 0.8 mg kg-1 min-1, p less than 0.025 at third level). Basal hepatic glucose production was also significantly reduced (from 4.3 +/- 0.4 to 3.3 +/- 0.3 mg kg-1 min-1, p less than 0.05), and residual glucose production further suppressed after insulin supplement (from 1.1 +/- 0.4 to 0.3 +/- 0.2 mg kg-1 min-1 after 120 min at 100 mU l-1 plasma insulin, p less than 0.05). Specific insulin binding to mononuclear leucocytes was unchanged (from 3.1 +/- 0.3 to 3.5 +/- 0.3%, NS).     

Treadmill training improves intravenous glucose tolerance and insulin sensitivity in fatty zucker rats

Summary The effect of treadmill training on intravenous glucose tolerance and insulin sensitivity was investigated in Zucker rats (fafa). In 25-week-old fafa animals with the typical metabolic syndrome of massive obesity, glucose intolerance, hypertriglyceridaemia and insulin resistance, treadmill exercise of only very mild intensity was carried out for 6 weeks. The training programme induced a marked reduction in basal and post-glucose challenge plasma insulin levels and a slight but significant improvement of intravenous glucose tolerance. No alteration in insulin sensitivity of the isolated perfused hindquarter was demonstrable. In another study a 9-week training programme was started in 7-week-old fafa rats before the development of their metabolic syndrome. In the sedentary control animals glucose intolerance and insulin resistance developed during the study period; in the training group, both the deterioration of glucose tolerance and the decrease of insulin sensitivity were prevented. This study demonstrates in fafa rats that (a) in young animals physical training may prevent a genetically predisposed deterioration of glucose tolerance and insulin sensitivity and (b) in adult animals mild physical training may improve intravenous glucose tolerance and insulin sensitivity.     

关于空腹血糖、空腹胰岛素乘积的倒数在流行病学研究中应用的补充说明

高胰岛素正糖钳夹技术可以测定活体的胰岛素敏感性,但它并不适用于大规模流行病学研究。流行病学研究需要简单的胰岛素抵抗测定法。本文补充报告在空腹血糖(FPG)(75～306mg/dl或4.2～17.1mmol/L)及空腹胰岛素(FIns)(9.7～120mU/L)范围很宽的Pima印第安人群中,正糖钳夹技术测定的胰岛素介导的葡萄糖代谢率(M)与涉及FPG、FIns的多种复合的胰岛素敏感指数的相关性:胰岛素作用指数(IAI)=1/(FPG×FIns)在非糖尿病人群及2型糖尿病人群都与M显著正相关(r>0.7,P=0.0001),而且这两者的相关性强于M与其他指数如FIns或FPG/FIns比值的相关性,也不弱于M与糖负荷后3～5个时间点的血糖、胰岛素曲线下面积乘积的相关性。IAI的五分变量分布情况表明有90.4%的IAI落在所预测的M值五分变量区域或与之相邻的一个五分变量区域之内。1/FPG×FIns虽相对简单但确实与机体的胰岛素敏感性密切相关,它可以做为胰岛素敏感指数在流行病学研究中应用。     

Impaired beta cell glucose sensitivity and whole-body insulin sensitivity as predictors of hyperglycaemia in non-diabetic subjects

Aims/hypothesis The aim of this prospective study was to investigate predictors of deteriorating glucose tolerance in subjects of British extraction. Methods A total of 156 non-diabetic subjects (86 with a family history of type 2 diabetes) underwent a 75-g OGTT and anthropometric assessment at baseline and 5 years later. Pancreatic beta cell function and whole-body insulin sensitivity were studied by model assessment. Subjects were classified as progressors if glucose tolerance moved one or more steps from normal, impaired fasting glucose, impaired glucose tolerance and diabetes over the follow-up period. Results At baseline, the progressors (n=22) had increased adiposity and a higher proportion of familial diabetes and abnormal glucose tolerance than non-progressors. Baseline pancreatic beta cell sensitivity to changes in glucose (p<0.02) and whole-body insulin sensitivity (p<0.0001) were decreased in the progressors. Logistic regression revealed that baseline and follow-up changes in beta cell glucose sensitivity and insulin sensitivity, rather than the classical clinical predictors (adiposity, familial diabetes and glucose levels), were the key independent predictors of progression (explaining over 50% of the progression). Conclusions/interpretation Impaired pancreatic beta cell glucose sensing and whole-body insulin sensitivity predict progression to hyperglycaemia. Strikingly, these pathophysiological changes override the importance of the clinical risk factors and highlight potential metabolic targets for prevention strategies. An erratum to this article can be found at     

Demonstration of a relatively hepatoselective effect of covalent insulin dimers on glucose metabolism in dogs

Summary Insulin analogues with relatively greater effect on hepatic glucose production than peripheral glucose disposal could offer a more physiological approach to the treatment of diabetes mellitus. The fact that proinsulin exhibits this property to a minor degree may suggest that analogues with increased molecular size may be less able than insulin to obtain access to peripheral receptor sites. Covalent insulin dimers have previously been shown to possess lower hypoglycaemic potencies than predicted by their in vivo receptor binding affinities. Reduced rates of diffusion to peripheral target tissues-might be an explanation for the lower in vivo potency compared to insulin. To test the relative hepatic and peripheral effects of covalent insulin dimers, glucose clamp procedures with D-[3-³H] glucose tracer infusions were used in anaesthetised greyhounds to establish dose-response curves for rates of hepatic glucose production and glucose disposal with insulin, N^B1, N^{B 1},-suberoyl-insulin dimer, and N^B29, N^{B 29},-suberoyl-insulin dimer. With N^B1, N^{B 1},-suberoyl-insulin dimer molar potencies relative to insulin were 68%, (34–133) (mean and 95% fiducial limits), for inhibition of hepatic glucose production and 14.7%, (10.3–20.9) for glucose disposal. With N^B29,N^{B 29},-suberoyl-insulin dimer potencies were 75%, (31–184) and 2.5%, (1.5–4.3), for inhibition of hepatic glucose production and for glucose disposal, respectively. The demonstration that both dimers exhibit a significantly greater effect on glucose production than on glucose disposal supports the suggestion that analogues with increased molecular size may exhibit reduced ability to gain access to peripheral target cells.Abbreviations B1-B 1D N^B1,N^{B 1},-suberoyl-insulin dimer - B29-B 29D N^B29,N^{B 29},-suberoyl-insulin dimer - Ra hepatic glucose production rate - Rd peripheral glucose disposal rate - M_r relative molecular weight - MCR metabolic clearance rate - ANOVA analysis of variance     

Impaired glucose tolerance is characterized by multiple abnormalities in the regulation of intermediary metabolism.

The responses of circulating intermediary metabolites to a low-dose sequential insulin infusion (basal, 0.005, 0.01, and 0.05 U kg-1 h-1) were assessed in eight non-obese men with Impaired Glucose Tolerance (IGT), and in eight healthy control subjects with normal glucose tolerance matched for age, gender, and body mass index. Fasting hyperinsulinaemia was observed in the subjects with IGT (7.4 +/- 1.0 vs 2.9 +/- 0.3 mU I-1, p less than 0.001). While there was no significant difference (p greater than 0.1) in fasting venous glucose levels between the groups, fasting concentrations of lactate (p less than 0.02), alanine (p less than 0.01), and glycerol (p less than 0.05) were significantly elevated in the subjects with IGT. During the incremental insulin infusion, overall concentrations of glucose (p less than 0.05), lactate (p less than 0.05), alanine (p less than 0.05), glycerol (p less than 0.05), immunoreactive insulin (p less than 0.001), and C-peptide (p less than 0.01) were significantly higher in the subjects with IGT. Linear dose-response relationships (p less than 0.005) for circulating immunoreactive insulin (log) vs metabolite concentrations were demonstrated by analysis of variance for glucose, non-esterified fatty acids (NEFA), glycerol, and total ketone bodies. For glucose, glycerol, and NEFA, group dose-response regression lines for the subjects with IGT were displaced significantly to the right (p less than 0.001 for each) of those for the normal control subjects, implying insulin insensitivity. In addition to the recognized defect in glucose homeostasis, these results indicate impaired regulation of multiple aspects of intermediary metabolism including lipolysis in IGT.     

The effect of intravenous metformin on glucose metabolism during hyperglycaemia in type 2 diabetes.

A stepped intravenous metformin infusion was used in conjunction with the hyperglycaemic clamp technique to study the dose-response relationship of plasma metformin concentration with hepatic glucose production and peripheral glucose disposal in nine patients with Type 2 diabetes. The study was of double-blind crossover design, using NaCl infusion as control. Plasma metformin concentrations spanning the therapeutic range (1.64 +/- 0.13 mg l-1 and 6.57 +/- 0.61 mg l-1) were achieved. No differences in peripheral glucose disposal were demonstrated when compared with NaCl infusion (3.4 +/- 0.1 vs 3.6 +/- 0.2 (+/- SE) mg kg-1 min-1 and 3.4 +/- 0.2 vs 3.3 +/- 0.2 mg kg-1 min-1, respectively). There was also no difference in basal hepatic glucose production during metformin and NaCl infusion (2.7 +/- 0.3 vs 2.8 +/- 0.2 mg kg-1 min-1). No acute effect of metformin on hepatic glucose production or peripheral glucose disposal was observed, implying that a chronic persistent effect is more important in these respects than immediate effects consequent upon changes in plasma drug level.     

Evaluation of insulin release and insulin sensitivity through oral glucose tolerance test: differences between NGT,IFG, IGT,and type 2 diabetes mellitus. A cross-sectional and follow-up study

Abstract. We evaluated both insulin release (IR) and insulin sensitivity (IS) through a single oral glucose tolerance test (OGTT) (blood samples at 0, 60, 120 min, as routinely performed in Europe) in subjects with normal and abnormal glucose tolerance. The value 1/HOMA was used as an index of IS and I/G at 60 min was used as an index of IR. In preliminary experiments, 1/HOMA correlated with glucose infusion rate (GIR) at euglycaemic insulin clamp (r=0.495) and with insulin sensitivity index (ISI) at LDIGIT (r=0.714). At OGTT with blood samples at 0, 30, 60 and 120 min, insulin levels at 30 min correlated with insulin levels at 60 min (I30 vs. I60, r=0.584) and I/G at 30 and at 60 min correlated (r=0.365). Values of 1/HOMA from 345 subjects with normal glucose tolerance (NGT), 32 with impaired fasting glucose (IFG), 186 with impaired glucose tolerance (IGT) and 72 with type 2 diabetic mellitus were divided into quartiles. For each quartile, mean (± SE) and 95% confidence intervals (CI) of I/G at 60 min were calculated, and subjects were represented by plotting IS vs. IR. Plots of NGT, IGT, and type-2 diabetes mellitus described different curves. Values of subjects with IFG, IGT and type 2 diabetes mellitus fell outside the 95% CI of NGT subjects in all quartiles of IS. To validate this finding, 113 morbidly obese subjects (basal OGTT: 55 NGT, 40 IGT, 18 T2DM) who underwent a major reduction of body weight through bariatric surgery received a second OGTT one year after surgery. Glucose tolerance improved in 40 patients, deteriorated in 8, did not change in 65; the new plots were concordant with the new class of glucose tolerance. OGTT can be used to evaluate both IR and IS in subjects with NGT, IFG, IGT, and type 2 diabetes mellitus in population studies and in follow-up studies. IFG, IGT and type 2 diabetes mellitus are characterized by reduced IR compared to IS.     

大黄酸改善糖尿病大鼠空腹血糖、胰岛素敏感性并增强肝脏PPARγ和GLUT-2的表达

目的 探讨大黄酸改善高脂喂养联合链脲佐菌素(STZ)诱导糖尿病大鼠血糖及肝脏胰岛素敏感性的作用及其可能机制.方法 (1)55只雄性Wistar大鼠随机分为正常对照组(NC,n=15)和糖尿病组(DM,n=40).NC组以基础饲料喂养,DM组以高脂饲料喂养5周后给予一次性腹腔注射STZ(30ms/kg),其中30只成模大鼠再分为糖尿病模型组(DM-C)和糖尿病大黄酸治疗组(DM-T),后者即开始大黄酸灌胃(100 mg·kg-1·d-1),灌胃11周后处死动物,收集标本,记录体重、肝重,测定空腹血糖(FBG)、甘油三酯(TG)、总胆同醇(TC)、HbA1C、糖化血清蛋白(GSP)等生化指标,放射免疫法测定血清胰岛素浓度(FINS),计算胰岛素敏感指数(ISI)及稳态模型评估的胰岛素抵抗指数(HOMA-IR).(2)免疫组化法检测肝脏组织中PPARγ的表达,Western印迹法检测肝脏组织中葡萄糖转运蛋白2(GLUT-2)表达.结果 实验结束时,测得DM-C组FBG[(22.57±3.23 vs 7.11±1.44)mmoL/L,P<0.01]、TG[(0.89±0.29 vs 0.58±0.17)mmoL/L,P<0.01]、HbA1C[(12.49±1.96 138 8.36±0.84)%,P<0.01]、GSP[(57.29±4.14 vs13.43±2.70)μmol/L,P<0.01]和肿瘤坏死因子α[TNF-α,(1.365±0.133 vs 1.233±0.159)μg/L,P<0.05]较NC组均显著升高.DM-C组肝重指数亦明显高于NC组(0.032±0.004 vs 0.024±0.002,P<0.01),FINS与NC组无明显差别,ISI较NC组下降明显[In(ISI),-5.46±0.61 vs -4.81±0.75,P<0.05],HOMA-IR较NC组升高[In(HOMA-IR),2.34±0.64 vs 1.70±0.78,P<0.05].DM-C组肝脏PPARγ [11 131.7(5 723.1-18 979.4) vs 48 782.1(21 576.7-108 829.5),P<0.01]和GLUT-2(0.98±0.35vs 1.29±0.27,P<0.05)表达较NC组有明显下降趋势.而DM-T组大鼠的FBG[(15.94±3.16)mmol/L]、HbA1C[(10.51±1.74)%]和GSP[(47.31±6.09)μmol/L]、In(HOMA-IR)(1.86±0.30)等较DM-C组均显著降低(P<0.05或P<0.01),In(ISI)(-4.97±0.29)较DM-C组升高明显(P<0.05).肝脏PPARγ/[35 156.3(24 554.3-86 660.9)],GLUT-2(1.55±0.55)蛋白表达水平较DM-C组明显增强(P<0.05或P<0.01).结论 大黄酸可降低糖尿病大鼠血糖、HbA1C及GSP、改善糖尿病大鼠胰岛素敏感性,其机制可能与增强PPARγ、GLUT-2蛋白表达有关.     

Effects of glycogen stores and non-esterified fatty acid availability on insulin-stimulated glucose metabolism and tissue pyruvate dehydrogenase activity in the rat

Summary The effects of increased tissue glycogen stores on insulin sensitivity, and on the response of insulin-stimulated glucose utilisation to an acute elevation in plasma fatty acid levels (1.5mmol/l), were investigated in conscious rats using the hyperinsulinaemic euglycaemic clamp. Studies were performed in two groups of rats; (a) fasted 24 h; (b) fasted 4.5 h, but infused with glucose for 4 h (0.5 g/h) of this period before the clamp (fed, glucose infused rats). Clamp glucose requirement and 3-³H-glucose turnover were 20–25% lower in the fed, glucose-infused rats. In these rats, elevation of plasma fatty acid levels resulted in impaired suppression of hepatic glucose output (residual hepatic glucose output: 41±4 vs 8±6 mol·min^–1·kg^–1. p < 0.001) but did not further decrease 3-³H-glucose turnover. Elevated nonesterified fatty acid levels had no significant effect on glucose kinetics in 24 h fasted rats. In the fed glucose-infused rats, at low plasma fatty acid levels, there was no deposition of glycogen in muscle during the clamp and liver glycogen levels fell. With elevation of non-esterified fatty acid levels muscle glycogen deposition was stimulated in both groups, and there was no fall in liver glycogen during the clamps in the fed glucose-infused rats. Increased non-esterified fatty acid availability during the clamps decreased pyruvate dehydrogenase activity in liver, heart, adipose tissue and quadriceps muscle, in both groups of rats. The findings are consistent with an inhibition of glycolysis in liver, skeletal muscle and heart by increased fatty acid availability. Increased glycogen synthesis, however, compensates for decreased glycolytic flux so that glucose turnover is not decreased. When liver glycogen stores are high, an acute increase in non-esterified fatty acid availability impairs suppression of hepatic glucose output. A chronic increase in non-esteriefid fatty acid availability may lead to insulin resistance by increasing glycogen stores.     

Effects of non-esterified fatty acid availability on insulin stimulated glucose utilisation and tissue pyruvate dehydrogenase activity in the rat

Summary Fatty acids in cardiac muscle compete with glucose for oxidation, thereby inhibiting glucose utilisation. It is not clear whether a similar mechanism is important in resting skeletal muscle. We used the hyperinsulinaemic euglycaemic clamp technique in conscious rats fasted for 20 h to examine the effects of increased plasma non-esterified fatty acid levels (1 mmol/l) on glucose metabolism. Insulin was infused at 75 mU/h (plasma insulin, 2.27±0.21 g/l) or 300mU/h (16.41±0.47 g/l). An increase in non-esterified fatty acid levels decreased clamp glucose requirement and 3–³H-glucose turnover by 35% (p<0.001) when the higher insulin dose was used but there was no change at the lower dose. At both insulin infusion rates, clamp blood lactate and pyruvate responses suggested inhibition of muscle glycolysis by elevated plasma non-esterified fatty acid concentrations. Quadriceps muscle glycogen deposition during the clamps was enhanced by increased non-esterified fatty acid availability at the lower insulin dose (p<0.001) but not at the higher insulin concentration. Activation of pyruvate dehyrogenase during the clamps was partially inhibited by increased plasma non-esterified fatty acid in the heart, adipose tissue and quadriceps muscle. This was evident at both insulin levels in heart but only at the higher insulin concentration in muscle (p<0.002). The findings are consistent with an inhibition of glycolysis in skeletal muscle of mixed fibre type as a result of increased fatty acid availability. At low rates of glucose flux glycogen synthesis may compensate for decreased glycolysis so that glucose turnover is not decreased. The role of pyruvate dehydrogenase in the glucose-fatty acid cycle in muscle may depend on the prevailing plasma insulin concentration and the degree of activation of this enzyme.