Characterisation of beta-cell dysfunction of impaired glucose tolerance: Evidence for impairment of incretin-induced insulin secretion

Aims/hypothesis. Our studies were undertaken to characterise the defective insulin secretion of impaired glucose tolerance (IGT).¶Methods. We studied 13 normal glucose tolerant subjects (NGT) and 12 subjects with IGT carefully matched for age, sex, BMI and waist-to-hip ratio. A modified hyperglycaemic clamp (10 mmol/l) with a standard 2-h square-wave hyperglycaemia, an additional glucagon-like-peptide (GLP)-1 phase (1.5 pmol · kg^–1· min^–1 over 80 min) and a final arginine bolus (5 g) was used to assess various phases of insulin secretion rate.¶Results. Insulin sensitivity during the second phase of the hyperglycaemic clamp was low in both groups but not significantly different (0.12 ± 0.021 in NGT vs 0.11 ± 0.013 μmol · kg^–1· min^–1· pmol^–1 in IGT, p = 0.61). First-phase insulin secretion was lower in IGT (1467 ± 252 vs 3198 ± 527 pmol · min^–1, p = 0.008) whereas the second phase was not (677 ± 61 vs 878 ± 117 pmol · min^–1, p = 0.15). The acute insulin secretory peak in response to GLP-1 was absent in IGT subjects who only produced a late phase of GLP-1-induced insulin secretion rate which was lower (2228 ± 188 pmol · min^–1) than in NGT subjects (3056 ± 327 pmol · min^–1, p = 0.043). Insulin secretion in response to arginine was considerably although not significantly lower in IGT subjects. The relative impairment (per cent of the mean rate for NGT subjects) was greatest for the GLP-1 peak (19 ± 9 %).¶Conclusion/interpretation. In this Caucasian cohort a defective insulin secretion rate is essential for the development of IGT. The variable degrees of impairment of different phases of the insulin secretion rate indicate that several defects contribute to its abnormality in IGT. Defects in the incretin signalling pathway of the beta cell could contribute to the pathogenesis of beta-cell dysfunction of IGT and thus Type II (non-insulin-dependent) diabetes mellitus. [Diabetologia (2000) 43: 852–858]     

糖耐量受损者胰岛素敏感性及胰岛β细胞功能的研究

目的 研究糖耐量受损(IGT)者的胰岛素抵抗(IR)及胰岛β细胞功能变化。方法 选取正常糖耐量(NGT)、IGT、2型糖尿病(T2DM)者共34例，以高胰岛素正血糖钳夹技术测定IR，行静脉葡萄糖耐量试验评估胰岛β细胞分泌功能。结果 与NGT组相比，IGT组、T2DM组的IR显著升高；IGT组胰岛素第一时相分泌明显下降，空腹胰岛素(FIns)水平及第二时相分泌水平升高；T2DM组IR与IGT组处于同一水平，FIns较NGT组显著减少。结论 由NGT向IGT的演变过程中，IR和胰岛素分泌缺陷共同起作用。     

Hypertension,insulin, and proinsulin in participants with impaired glucose tolerance

The association of insulin resistance and hyperinsulinemia to blood pressure has remained controversial. We examined the association of insulinemia to hypertension and blood pressure using baseline measurements for participants of the Diabetes Prevention Program (DPP). The DPP is a multicenter randomized controlled trial of 3819 participants with impaired glucose tolerance, and is designed to evaluate interventions for the delay or prevention of type 2 diabetes. The relationship between hypertension and insulinemia is described overall and by ethnicity. The effects of demographics (age and gender), adiposity, and glucose on the relationship are also presented. Asian Americans and African Americans had a similarly high prevalence of hypertension as did whites; American Indians had a lower prevalence of hypertension. Among participants not on antihypertensive medications, systolic blood pressure was significantly (but weakly) correlated with fasting insulin (r=0.12), homeostasis model assessment of insulin resistance (HOMA IR; r=0.13), and fasting proinsulin (r=0.10) when adjusted for age and gender (all, P<0.001). Systolic blood pressure showed similar correlations to fasting insulin in each ethnic group. After further adjustment for body mass index, the association of fasting insulin to systolic and diastolic blood pressures weakened considerably but remained significant (systolic: r=0.06, P=0.002; DBP: r=0.06, P<0.001). We conclude that a weak but significant association between insulin, (and proinsulin and HOMA IR) and blood pressure exists but is largely explained by overall adiposity. This association is similar among ethnicities, with the possible exception of Hispanics. The relation between insulin concentrations and blood pressure explains relatively little of the ethnic differences in hypertensive prevalence.     

Predominant role of reduced beta-cell sensitivity to glucose over insulin resistance in impaired glucose tolerance

Aims/hypothesis Impaired glucose tolerance (IGT) is an insulin-resistant state and a risk factor for Type 2 diabetes. The relative roles of insulin resistance and insulin deficiency in IGT have been disputed.Methods In 40 IGT subjects and 63 sex-, age-, and weight-matched controls with normal glucose tolerance (NGT), we measured (i) indices of insulin sensitivity of fasting glucose production (by tracer glucose) and glucose disposal (M value on a 240 pmol·min^–1·m^–2 insulin clamp) and (ii) indices of beta-cell function (glucose sensitivity, rate sensitivity, and potentiation) derived from model analysis (Am J Physiol 283:E1159–E1166, 2002) of the insulin secretory response (by C-peptide deconvolution) to oral glucose.Results In comparison with NGT, IGT were modestly insulin resistant (M=29±2 vs 35±2 µmol·min^–1·kg_FFM^–1, p=0.01); insulin sensitivity of glucose production also was reduced, in approximate proportion to M. Despite higher baseline insulin secretion rates, IGT was characterized by a 50% reduction in glucose sensitivity [53 (36) vs 102 (123) pmol·min^–1·m^–2·mM^–1, median (interquartile range), p=0.001] and impaired potentiation [1.6 (0.8) vs 2.0 (1.5) units, p<0.04] of insulin release, whereas rate sensitivity [1.15 (1.15) vs 1.38 (1.28) nmol·m^–2·mM^–1] was not significantly reduced. Glucose sensitivity made the single largest contribution (~50%) to the observed variability of glucose tolerance.Conclusion/interpretation In IGT the defect in glucose sensitivity of insulin release quantitatively predominates over insulin resistance in the genesis of the reduced tolerance to oral glucose.     

Rosiglitazone improves insulin sensitivity and glucose tolerance in subjects with impaired glucose tolerance

OBJECTIVE: This study was designed to evaluate the effects of rosiglitazone (ROS) on insulin sensitivity, beta-cell function, and glycaemic response to glucose challenge and meal in subjects with impaired glucose tolerance (IGT). METHODS: Thirty patients with IGT (ages between 30 and 75 years and BMI (body mass index) < or = 27 kg/m2) were randomly assigned to receive either placebo (n = 15) or ROS (4 mg/day) (n = 15). All participants underwent a 75-g oral glucose tolerance test (OGTT), meal test, and frequently sampled intravenous glucose tolerance test (FSIGT) before and after the 12-week treatment. RESULTS: After 12 weeks of ROS treatment, there were significant increases in total cholesterol (TC) (4.25 +/- 0.22 vs 4.80 +/- 0.17 mmol/l, P < 0.001), high-density lipoprotein cholesterol (HDL-C) (1.25 +/- 0.07 vs 1.43 +/- 0.06 mmol/l, P < 0.05), and low-density lipoprotein cholesterol (LDL-C) (2.70 +/- 0.15 vs 3.37 +/- 0.17 mmol/l, P < 0.05) without changes in triglyceride concentration, TC/HDL-C and LDL-C/HDL-C ratio. Although the acute insulin response (AIR) to intravenous glucose and disposition index (measured as the ability of pancreatic beta-cell compensation in the presence of insulin resistance) remained unchanged, the insulin sensitivity (SI) and glucose effectiveness (SG) were remarkably elevated (0.38 +/- 0.06 vs 0.54 +/- 0.09 x 10(-5) min(-1)/pmol, P < 0.05; 0.017 +/- 0.002 vs 0.021 +/- 0.001 min(-1), P < 0.05, respectively) in the ROS group. The glucose, insulin, and c-peptide areas under curve (AUC) in response to OGTT and the glucose and insulin AUC during meal were significantly ameliorated in the ROS group. Five out of 15 (33%) and two out of 15 (13%) subjects treated with ROS and placebo, respectively, reversed to normal response during OGTT (P < 0.05). CONCLUSION: Rosiglitazone treatment significantly improved insulin resistance and reduced postchallenge glucose and insulin concentrations in patients with impaired glucose tolerance without remarkable effects on beta-cell secretory function.     

肥胖和非肥胖糖耐量受损患者胰岛素敏感性和1相胰岛素分泌研究

目的研究肥胖和非肥胖糖耐量受损(IGT)患者的胰岛素敏感性和β细胞1相胰岛素分泌功能,以探讨在IGT患者中肥胖对胰岛素抵抗和1相胰岛素分泌的影响。方法共有99位受试者(包括正常对照者32名,肥胖IGT44例,非肥胖IGT23例)接受了口服75 g葡萄糖耐量试验(OGTT)和胰岛素改良的减少样本数(采血样12次)的Bergman微小模型技术结合静脉葡萄糖耐量试验(FSIGTT)。胰岛素抵抗由FSIGTT中胰岛素敏感性指数(SI)加以评估,而OGTT中糖负荷后30 min胰岛素增值与血糖增值之比值[ΔI30/ΔG30=(I30 min-I0 min) /(G30 min-G0 min)]和FSIGTT中急性胰岛素分泌反应(AIRg)则用以评价胰岛β细胞分泌功能。处理指数(DI =AIRg×SI)用于评价AIRg是否代偿机体的胰岛素抵抗。结果与正常对照组[(7.52±10.89)×10-4]相比,二组IGT患者之SI明显降低,而肥胖IGT组的SI[(1.72±1.11)×10-4]较非肥胖组[(3.15±1.49)×10-4]更低(均P<0.01); AIRg和ΔI30/ΔG30在正常组(412±191,14.45±8.47)和肥胖IGT组(378±235,17.02±11.30)之间差异无统计学意义,但均大于非肥胖组(196±160,8.93±6.69,均P<0.01);与正常组(2 851±1 180)相比,DI指数在二组IGT显著降低(595±485,584±517),但后二组间此值差异无统计学意义。SI与2 h胰岛素、体重指数、尿酸和胆固醇呈显著的负相关性(校正r2=0.603,P<0.01);而AIRg与ΔI30/ΔG30显著正相关,与空腹血糖负相关(校正r2=0.479,P<0.01)。结论IGT患者存在胰岛素抵抗和β细胞功能异常。与非肥胖IGT患者相比,肥胖IGT患者胰岛素抵抗程度更为严重,但胰岛β细胞胰岛素1相分泌相对充分。     

新疆汉、维民族糖调节受损人群胰岛素分泌功能和胰岛素作用功能的研究

目的 评估新疆汉、维民族在IFG,IGT及IGR阶段的胰岛素分泌功能和胰岛素作用功能。 方法 采用多中心研究进行横断面调查,行OGTT试验。用胰岛素抵抗指数（HOMA-IR）评估IR,胰岛β细胞功能指数（HOMA-β）评估基础胰岛素分泌;ΔI30/ΔG30评价胰岛素早相分泌,ΔI30/ΔG30/HOMA-IR评估葡萄糖处置指数（DI）。 结果 WC、BMI、血脂、FIns、2 hIns在汉、维民族不同糖代谢组差异有统计学意义。IFG组与NGT、IGT组比较,汉、维族人群的HOMA-IR差异有统计学意义。在汉族中NGT组与IGT、IGR组比较,HOMA-β差异有统计学意义（P=0.030、0.044）,而在维族只有IFG组与NGT组比较差异有统计学意义（P=0.001）。ΔI30/ΔG30、DI在两民族不同糖代谢组差异均无统计学意义。 结论 汉族人群IR在IFG阶段,胰岛素分泌功能在IGT阶段起主要作用。IR和胰岛素分泌功能在维族人群IFG阶段起重要作用。胰岛素早相分泌及葡萄糖处置功能在糖调节受损阶段作用不显著。     

Peripheral and hepatic insulin sensitivity in subjects with impaired glucose tolerance

Summary Recent evidence suggests that the post-prandial hyperglycaemia in impaired glucose tolerance is primarily due to impaired suppression of basal hepatic glucose output. This in turn appears to be secondary to decreased first phase insulin secretion, although decreased hepatic insulin sensitivity, which is a feature of non-insulin-dependent diabetes mellitus, might also play a role. Eight mildly overweight subjects with impaired glucose tolerance and eight closely matched control subjects with normal glucose tolerance underwent an intravenous glucose tolerance test to assess first phase insulin secretion. Insulin sensitivity was examined by a 150-min hyperinsulinaemic-euglycaemic clamp. Somatostatin was infused from 150 min to suppress endogenous insulin secretion, and glucagon and insulin were replaced by constant infusion. Glucose with added dideuterated glucose (labelled infusion technique) was infused to maintain euglycaemia. First phase insulin secretion ( 0–10 min insulin area ÷ 0–10 min glucose area) was significantly decreased in the subjects with impaired glucose tolerance (median [range]: 1.2 [0.2–19.4] vs 9.1 [2.6–14.5] mU·mmol^–1; p<0.01). During the clamp, circulating insulin (93±8 [mean±SEM] and 81±10 mU·l^–1) and glucagon (54±4 and 44±6 ng·l^–1) levels were comparable. Total glucose disposal was decreased in subjects with impaired glucose tolerance (2.78±0.27 vs 4.47±0.53 mg·kg^–1·min^–1; p<0.02), and was primarily due to decreased non-oxidative glucose disposal. However, hepatic glucose output rates were comparable during the clamp (0.38±0.10 and 0.30±0.18 mg·kg^–1·min^–1). Therefore, the main defects in subjects with impaired glucose tolerance are decreased first phase insulin secretion and peripheral non-oxidative glucose disposal, but hepatic glucose output shows normal responsiveness to insulin.Abbreviations FPIS First phase insulin secretion - PG plasma glucose - NIDDM non-insulin-dependent diabetes mellitus - IGT impaired glucose tolerance - HGO hepatic glucose output - IVGTT intravenous glucose tolerance test - OGTT oral glucose tolerance test     

空腹血糖异常人群胰岛素分泌功能及胰岛素抵抗状态的探讨

目的　探讨空腹血糖异常人群的胰岛素分泌及胰岛素抵抗状态。　方法　选择包钢糖尿病普查中复查口服葡萄糖耐量试验 (OGTT) 3985例 ,分为 6组 :正常糖耐量 (NGT)组 2 5 88例 ,异常空腹血糖 (IFG)组 2 72例 ,糖耐量减低 (IGT)组 4 4 9例 ,空腹血糖异常伴糖耐量减低 (IFG/ IGT)组116例 ,新诊断糖尿病 (DM1)组 338例 ,已知糖尿病 (DM2 )组 2 2 2例。测腰围、体重指数、血压、血脂及血浆胰岛素 ,应用稳态模式胰岛素抵抗指数 (HOMA- IR)作为胰岛素抵抗指标 ,稳态模式胰岛 β细胞功能指数 (HBCI)及胰岛素分泌指数 (IS)作为胰岛素分泌指标 ,并对 6组患者的这些指标及临床特征 ,进行对比分析。　结果　与 NGT组比较 ,IFG组 HOMA- IR(1.4 6± 0 .6 0 ,1.0 6± 0 .6 4 ,t=- 6 .716 ,P<0 .0 0 1)、空腹胰岛素 (FINS) (17.90± 10 .0 6 ,15 .79± 10 .94 ,t=- 2 .0 71,P=0 .0 39)增高 ,HB-CI(4.6 5± 0 .6 0 ,5 .2 7± 0 .76 ,t=3.399,P<0 .0 0 1)及 IS(0 .86± 0 .6 0 ,0 .99± 0 .6 2 ,t=2 .36 6 ,p=0 .0 18)降低 ;IGT组 HOMA- IR(1.39± 0 .5 8,t=4 .6 98) ,FINS(2 1.2 7± 15 .39,t=4 .4 93)、2 - h胰岛素(6 0 .84± 37.86 ,t=8.4 82 )、HBCI(5 .4 7± 0 .79,t=2 .6 98)、IS(1.2 5± 0 .6 1,t=4 .0 34,P值均 <0     

The effect of long-term glibenclamide treatment on glucose tolerance, insulin secretion and serum lipids in subjects with impaired glucose tolerance

The effects of glibenclamide plus diet (n = 27) or diet alone (n = 18) on glucose tolerance, insulin secretion and serum lipids in non-obese subjects with normal or low insulin responses and impaired glucose tolerance (IGT) has been followed up for two years. Glucose tolerance and insulin secretion were characterized by means of a glucose infusion test consisting of an initial injection of 0.33 g glucose/kg body weight followed by 12 mg/kg body weight/min for 2 h. Dietary treatment did not improve glucose tolerance in normal and low insulin-responders. Glibenclamide plus diet succeeded in improving glucose tolerance only in low insulin responders whereas glucose tolerance remained unchanged in normal insulin responders. There was a significant decrease in fasting and glucose-stimulated insulin levels after two years of glibenclamide treatment in both the normal and low insulin-responders. The body weight was not altered. Triglyceride and cholesterol levels both decreased. In summary, the present study failed to demonstrate an increase in insulin secretion under chronic administration of glibenclamide in subjects with IGT independent of the type of insulin response. From the practical point of view, glibenclamide is of benefit in the treatment of non-obese subjects with IGT and relative insulin deficiency.     

糖调节受损个体胰岛β细胞功能和胰岛素抵抗观察

评价152例人选者[正常糖耐量、空腹血糖受损和(或)糖耐量受损]胰岛β细胞功能和胰岛素抵抗.结果 显示空腹血糖受损者主要表现胰岛素早期分泌功能缺陷和基础分泌不足,胰岛素抵抗严重;糖耐量受损者则胰岛素早期和晚期分泌功能显著下降伴轻度胰岛素抵抗.     

Evaluation of insulin resistance in non-obese subjects with impaired glucose tolerance

Insulin resistance was estimated in nine subjects with impaired glucose tolerance (IGT) and eleven healthy, age and body-weight matched controls. Glucose tolerance and insulin response were evaluated by means of a 2h-glucose infusion test. Insulin resistance was determined by measuring the steady state plasma glucose response (SSPG) to a continuous infusion of glucose (6 mg . kg-1 . min-1 or 12 mg . kg-1 . min-1), insulin, epinephrine and propranolol for 150 minutes as described previously by other authors. The endogenous insulin secretion (C-peptide) was inhibited by epinephrine and propranolol in controls and subjects with IGT irrespective of a low (6 mg . kg-1 . min-1) or high (12 mg . kg-1 . min-1) glucose infusion. Steady-state plasma levels of exogenous insulin were virtually identical in all groups studied. There were no significant differences in the pancreatic glucagon, growth hormone, FFA and glycerol response during the SSPG period between controls and subjects with IGT. In comparison to controls the mean SSPG was significantly higher in subjects with IGT (during low and high glucose infusion) suggesting the existence of insulin resistance in these subjects. A higher glucose dose as described earlier by other investigators does not provide a better discrimination of controls and subjects with IGT concerning their degree of insulin resistance. Finally, there was a direct correlation between the SSPG and glucose tolerance in the total group. In conclusion, our results have confirmed the validity of an infusion technique of glucose, insulin, epinephrine and propranolol for evaluation of insulin sensitivity in vivo. In addition, our findings have added further support for insulin resistance in subjects with IGT which is directly proportional to the degree of glucose intolerance.     

Impaired beta-cell function and insulin sensitivity in Japanese subjects with normal glucose tolerance

The development of type 2 diabetes mellitus is characterized by both impaired beta-cell function and increasing insulin resistance. To clarify the roles of them in developing type 2 diabetes, we evaluated insulin resistance by HOMA-IR and insulin secretion by HOMA beta-cell in 453 Japanese subjects whose fasting plasma glucose (FPG) and HbA(1c) levels were within normal range. HOMA beta-cell was found to decrease in the over 30 years groups, while HOMA-IR increased with body mass index (BMI). To analyze the reserve capacity of insulin secretion and insulin sensitivity, the 67 of them, who underwent a standard oral glucose tolerance test and were diagnosed with normal glucose tolerance (NGT), were divided into four degrees of BMI age-adjusted to 50 years. They were compared for insulinogenic index and ISI composite proposed by Matsuda and DeFronzo across the range of BMI. ISI composite was significantly less in the highest BMI group, while insulin secretion did not increase in the higher BMI groups. The subjects with higher BMI had remarkably lower insulinogenic indices than those with lower BMI. These data suggest that insulin secretory reserve is insufficient to compensate for increased insulin resistance in Japanese people with NGT at about 50 years of age.     

Pancreatic beta-cell function and insulin sensitivity in japanese subjects with impaired glucose tolerance and newly diagnosed type 2 diabetes mellitus

To clarify whether pancreatic beta-cell function and/or insulin resistance contributes to development of glucose intolerance in Japanese subjects, we investigated 551 subjects who underwent a 75-g oral glucose tolerance test (OGTT). Subjects were divided into 3 groups: normal glucose tolerance (NGT, n = 238), impaired glucose tolerance (IGT, n = 211), and newly diagnosed type 2 diabetes mellitus (n = 102). The diabetics were subdivided into 3 subgroups as follows: diabetes with normal fasting glucose (fasting plasma glucose [FPG] < 110 mg/dL), diabetes with impaired fasting glucose (FPG 110 to 125 mg/dL), and diabetes with diabetic fasting glucose (FPG >or= 126 mg/dL). Insulinogenic index as early-phase insulin secretion, homeostasis model assessment (HOMA-beta and HOMA-resistance), and 4 different formulas of insulin sensitivity index were assessed by plasma glucose and insulin concentrations obtained at fasting or during a 75-g OGTT. Both early-phase insulin secretion and insulin sensitivity were low even in the IGT stage compared with NGT. The transition from IGT to diabetes was accompanied by a progressive deterioration of insulin reserve as well as insulin resistance. During the further progression in diabetes, insulinogenic index decreased additionally, whereas declines in insulin sensitivity were relatively small. In conclusion, both impaired insulin secretion and insulin resistance may contribute to the underlying mechanisms of glucose intolerance in Japanese subjects.     

Effect of pioglitazone on insulin secretion in patients with both impaired fasting glucose and impaired glucose tolerance

AIM: To evaluate the effect of a thiazolidinedione, pioglitazone, on insulin secretion in patients with both impaired fasting glucose and impaired glucose tolerance. METHODS: A randomized, double-blind, placebo-controlled clinical trial was carried out in 18 overweight or obese patients with both impaired fasting glucose and impaired glucose tolerance. Pharmacological intervention consisted of an oral morning administration of pioglitazone (30 mg) or a placebo with a similar presentation for 30 days. Before and after the intervention, glucose, creatinine, lipid profile and uric acid concentrations were measured. To evaluate insulin secretion (early, late and total phases) and insulin sensitivity, a hyperglycemic-hyperinsulinemic clamp was also performed. RESULTS: There were significant reductions (p=0.008) in fasting insulin concentration (121 versus 45 pmol/l), late (565 versus 307 pmol/l) and total insulin secretion (474 versus 254 pmol/l), as well as, in 2h postload glucose levels (9.7 versus 6.9 mmol/l, p=0.028), with an increment in insulin sensitivity after pioglitazone administration (7.5 versus 9.9). CONCLUSION: Pioglitazone administration during a period of 4 weeks decreased late and total insulin secretion phases, fasting insulin and 2h postload glucose levels, and improved insulin sensitivity in patients with both impaired fasting glucose and impaired glucose tolerance.     

不同糖耐量水平人群血清真胰岛素和胰岛素原水平的临床意义

目的 探讨不同糖耐量者血清真胰岛素（ＴＩ）及胰岛素原（ＰＩ）水平的变化及临床意义。方法 用特异的单克隆抗体夹心放大酶联免疫分析法（ＢＡ－ＥＬＩＳＡ）检测１３５例正常糖耐量（ＮＧＴ）、８６例糖耐量低减（ＩＧＴ）及１０１例Ⅱ型糖尿病（ＤＭ）者口服葡萄糖耐量试验（ＯＧＴＴ）各点血清ＴＩ及ＰＩ水平。结果 ３组血清空腹ＴＩ差异无显著性（Ｐ〉０．０５）,免疫反应胰岛素（ＩＲＩ）Ⅱ型ＤＭ组明显升高（Ｐ〈０．０１     

Short-term exercise improves beta-cell function and insulin resistance in older people with impaired glucose tolerance

BACKGROUND: There is a high prevalence of diabetes and impaired glucose tolerance (IGT) in the older population. Normal aging is associated with insulin resistance and impaired insulin secretion, with greater defects in people with IGT. Short-term exercise has been found to increase insulin sensitivity, but little is known about acute exercise effects on beta-cell function in older people with IGT. METHODS: We assessed the effects of 7 consecutive days of supervised aerobic exercise (1 h/d at 60-70% heart rate reserve) in 12 sedentary older people with IGT. Screening included oral glucose tolerance test, stress/maximal O(2) uptake test, and dual-energy x-ray absorptiometry scan. Participants had a frequently sampled iv glucose tolerance test at baseline and 15-20 h after the seventh exercise session. Insulin sensitivity (S(I)), glucose disappearance constant (Kg, a measure of iv glucose tolerance), acute insulin response to glucose (AIRg), and disposition index (AIRg x S(I)), a measure of beta-cell function in relation to insulin resistance, were calculated. RESULTS: Exercise was well tolerated. Body weight, fasting glucose, fasting insulin, and iv glucose tolerance were unchanged with exercise. S(I) increased by 59%, AIRg decreased by 12%, and disposition index increased by 31%. There was no significant change in fasting lipid, catecholamine, leptin, or adiponectin levels. CONCLUSIONS: Short-term exercise not only improved insulin resistance but also significantly enhanced beta-cell function in older people with IGT. These effects of short-term exercise on beta-cell function cannot be explained by changes in body weight or circulating levels of lipids, leptin, adiponectin, or catecholamines.     

Evaluation of insulin resistance during inhibition of endogenous insulin and glucagon secretion by somatostatin in non-obese subjects with impaired glucose tolerance

Summary Insulin resistance was studied in seven non-obese male subjects with impaired glucose tolerance and four healthy, age and body-weight matched male control subjects by means of a continuous intravenous infusion of somatostatin, glucose and insulin over 150 min. Glucose tolerance was evaluated by means of a 2-h glucose infusion test. Endogenous insulin (C-peptide), growth hormone, and glucagon secretion were suppressed by somatostatin in both groups. Steady-state plasma insulin and glucose levels were achieved between 90–135 min. Since similar steady-state levels of exogenous insulin were achieved, the resulting steady-state plasma glucose level provided a direct estimate of the ability of insulin to dispose of the infused glucose. The glucose levels were higher in subjects with impaired glucose tolerance with values of 14.6 ± 1.8 mmol/1 compared with 5.1 ± 1.2 mmol/1 in control subjects (p < 0.01), thus indicating insulin resistance. There was a direct correlation between the steady-state plasma glucose level and glucose tolerance suggesting that the degree of glucose intolerance is proportional to the degree of insulin resistance. These results revealed that decreased insulin sensitivity is found in non-obese subjects with impaired glucose tolerance.     

Insulin secretion and incretin hormones after oral glucose in non-obese subjects with impaired glucose tolerance

Subjects with impaired glucose tolerance (IGT) are usually overweight and exhibit insulin resistance with a defective compensation of insulin secretion. In this study, we sought to establish the interrelation between insulin secretion and insulin sensitivity after oral glucose in non-obese subjects with IGT and we also examined this interrelation in relation to the 2 main incretins, glucagon-like peptide (GLP-1) and gastric inhibitory polypeptide (GIP). To that end, 13 women with IGT and 17 women with normal glucose tolerance (NGT) underwent an oral glucose tolerance test (OGTT) with measurements of glucose, insulin, C-peptide, GLP-1, and GIP. Insulin secretion (TIS) and insulin sensitivity (OGIS) were assessed using models describing the relationship between glucose, insulin and C-peptide data. These models allowed estimation also of the hepatic extraction of insulin. The age (54.2 +/- 9.7 [mean +/- SD] years) and body mass index (BMI; 26.0 +/- 4.0 kg/m(2)) did not differ between the groups. Subjects with IGT displayed lower TIS during the initial 30 minutes after oral glucose (0.97 +/- 0.17 [mean +/- SEM] v 1.75 +/- 0.23 nmol/L in NGT; P =.018) and lower OGIS (397 +/- 21 v 463 +/- 12 mL/min/m(2); P =.005). The incremental 30-minute TIS times OGIS (reflecting insulin secretion in relation to insulin sensitivity) was significantly reduced in IGT (359 +/- 51 v 774 +/- 91 nmol/min/m(2), P =.001). This measure correlated inversely to the 2-hour glucose level (r = -0.71; P <.001). In contrast, TIS over the whole 180-minute period was higher in IGT (26.2 +/- 2.4 v 20.0 +/- 2.0 nmol/L; P =.035). Hepatic insulin extraction correlated linearly with OGIS (r = 0.71; P <.001), but was not significantly different between the groups although there was a trend with lower extraction in IGT (P =.055). Plasma levels of GLP-1 and GIP increased after oral glucose. Total secretion of these incretin hormones during the 3-hour test did not differ between the 2 groups. However, the 30-minute increase in GLP-1 concentrations was lower in IGT than in NGT (P =.036). We conclude that also in non-obese subjects with IGT, when adiposity is controlled for in relation to NGT, defective early insulin secretion after oral glucose is a key factor. This defective beta-cell function is associated with, and may be caused by, a reduced early GLP-1 response.     

Early phase insulin secretion is increased in subjects with normal fasting glucose and metabolic syndrome: a premature feature of beta-cell dysfunction

Background and Aims

Metabolic syndrome (MS) has been mainly related to insulin resistance, but the role of changes in insulin secretion has not been thoroughly investigated.

Methods and Results

Using an oral glucose tolerance test (OGTT) we studied beta-cell function and insulin sensitivity in subjects with normal fasting glucose with and without MS, and their relationship to fatty liver which was evaluated by abdominal-ultrasonography. In MS early phase insulin secretion, as measured by insulinogenic index (IG₃₀), was increased (p < 0.05) independently from insulin sensitivity. Furthermore IG₃₀ was progressively higher as the number of factors needed for the diagnosis of MS increased (p < 0.01). Insulin and C-peptide AUC were also increased (p < 0.01 and p < 0.05, respectively) but, in contrast to IG_30, these differences disappeared when ISI was used as a covariate. After OGTT, 51% of the subjects with MS had altered post-load glucose tolerance compared to 24.9% without MS (p < 0.01). In both groups, the altered glucose tolerance was associated with a similar IG₃₀ reduction. In normo-tolerant subjects with MS the IG₃₀ was higher (+54.1%, p < 0.01), and this elevation occurred irrespective of ISI; however, the beta-cell compensatory capacity for insulin resistance (disposition index) was impaired (p < 0.001). Fatty liver was more frequent (p < 0.001) and more severe (p < 0.01) in MS, and it was significantly related to total AUC-insulin (p < 0.001), independently from ISI.

Conclusion

These findings indicate that the prevalence of altered tolerance is more frequent in subjects with normal fasting glucose and MS. The hyperinsulinemia might not only be an adaptive response to insulin resistance, but a primary defect of beta-cell function contributing to glucose intolerance.