On the interplay beween insulin secretion and sensitivity as determinants of glucose tolerance

Both insulin secretion and sensitivity have been claimed to be the main characteristics in the determination of future detoriation in glucose tolerance. In this cross-sectional study insulin secretion and insulin sensiturity were determined in 228 subjects with varying degrees of glucose tolerance. Insulin secretion was measured in an intravenous glucose tolerance test (IVGTT) and insulin sensitivity by the hyperinsulinaemic euglycaemic clamp test. Both the early insulin response in the IVGTT (increment) and the glucose disposal rate in the clamp test (M-value) were found to be related hyperbolically to fasting glucose (r=–0.63 and –0.66, respectively; bothP<0.0001) and in a second-order polynomial manner to the glucose disappearence rate (k-value) in the IVGTT (r=0.53 and 0.48, respectively; bothP<0.0001). Multiple regression analysis showed the insulin increment in the IVGTT and theM-value in the clamp test to be equally important determinants of glucose tolerance, together explaining about 50% of the variation in fasting glucose and thek-value in the IVGTT. In conclusion, in this cross-sectional study insulin secretion and sensitivity studied over a broad range of glucose tolerance were found to be of amost equal importance in the determination of glucose tolerance. However, low levels of insulin increment in the IVGTT were more often associated with glucose intolerance than was a low insulin sensitivity.     

Insulin sensitivity, insulin release and glucagon-like peptide-1 levels in persons with impaired fasting glucose and/or impaired glucose tolerance in the EUGENE2 study

Aims/hypothesis We examined the phenotype of individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) with regard to insulin release and insulin resistance. Methods Non-diabetic offspring (n = 874; mean age 40 ± 10.4 years; BMI 26.6 ± 4.9 kg/m²) of type 2 diabetic patients from five different European Centres (Denmark, Finland, Germany, Italy and Sweden) were examined with regard to insulin sensitivity (euglycaemic clamps), insulin release (IVGTT) and glucose tolerance (OGTT). The levels of glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) were measured during the OGTT in 278 individuals. Results Normal glucose tolerance was found in 634 participants, while 110 had isolated IFG, 86 had isolated IGT and 44 had both IFG and IGT, i.e. about 28% had a form of reduced glucose tolerance. Participants with isolated IFG had lower glucose-corrected first-phase (0–10 min) and higher second-phase insulin release (10–60 min) during the IVGTT, while insulin sensitivity was reduced in all groups with abnormal glucose tolerance. Similarly, GLP-1 but not GIP levels were reduced in individuals with abnormal glucose tolerance. Conclusions/interpretation The primary mechanism leading to hyperglycaemia in participants with isolated IFG is likely to be impaired basal and first-phase insulin secretion, whereas in isolated IGT the primary mechanism leading to postglucose load hyperglycaemia is insulin resistance. Reduced GLP-1 levels were seen in all groups with abnormal glucose tolerance and were unrelated to the insulin release pattern during an IVGTT.     

Peripheral insulin release after pancreatic resection: the effect of decreased beta-cell mass with systemic or portal drainage

Surgical alteration of the pancreas can result in several anatomic alterations which may affect insulin release. We evaluated the effects of resection, systemic drainage, and autotransplantation of the canine pancreas on peripheral insulin levels and glucose disposal as measured by iv glucose tolerance tests (IVGTT) and a steady state hyperglycemic challenge (clamp). Proximal pancreatectomy (PPx) with reduced beta-cell mass and intact portal drainage resulted in a modestly elevated fasting glucose level and increased integrated glucose response to IVGTT. Compared to preoperative normals, basal insulin was unchanged from preoperative controls; however, peak insulin and integrated insulin response to IVGTT were decreased in PPx animals. Splenocaval drainage or autotransplantation of the distal pancreas resulted in normalization of the severely altered insulin response and fasting glucose levels. K values were significantly reduced after all three procedures. Clamp studies confirmed the basal glucose and insulin findings of the IVGTT. During the clamp, PPx animals had peripheral insulin values approximately 50% of normal controls, while autotransplantation and splenocaval drainage animals had insulin values that approximate normal controls. All three postsurgical groups had blunted insulin levels during stable hyperglycemia. Glucose utilization rates were severely decreased in all three groups. Reduction of beta-cell mass with intact portal drainage resulted in reduced insulin response to glucose challenge by either IVGTT or clamp. Systemic drainage of this same reduced beta-cell mass resulted in peripheral insulin levels comparable to normal controls. Denervation (autotransplantation) had little additive effect. All three groups demonstrated severely decreased rates of glucose disappearance as measured by both IVGTT and clamp studies. Therefore, reduction in beta-cell mass, drained systemically or portally, results in altered glucose disposal regardless of the peripheral insulin levels.     

Assessment of insulin sensitivity from plasma insulin and glucose in the fasting or post oral glucose-load state.

OBJECTIVE: To compare insulin sensitivity indexes derived from plasma insulin (I) and glucose (G) in the basal state (Sib) and at the second hour (I2h and G2h) of an oral glucose tolerance test (OGTT, Si2h) (i) with measurements of insulin sensitivity using the insulin modified frequently sampled intravenous glucose tolerance test (FSIVGTT) [Si(IVGTT)] and (ii) with modelling of fasting glucose and insulin by the homeostasis model assessment (HOMA). SUBJECTS: 47 subjects entered the study. 31 subjects were classified as having normal glucose tolerance (NGT), 10 as having impaired tolerance to glucose (IGT) and six as type 2 diabetes mellitus according to the World Health Organisation (WHO) criteria. MEASUREMENTS: Sib and Si2h were calculated as follows. Sib = 10(8)/(I x G x VD), Si2h = 10(8)/(I2hr x G2hr x VD) where VD is an estimate of the apparent glucose distribution volume. A third insulin sensitivity index (SiM) was calculated by averaging Sib and Si2h. HOMA was calculated as follows: I/(22.5 x e(-lnG)) RESULTS: Si(IVGTT), Sib, SI2h and SiM were all significantly higher in subjects with NGT than in those with IGT or type 2 diabetes. Si(IVGTT) was highly correlated (P < or = 0.0001) with the three insulin sensitivity indexes found in the total population, in subjects with NGT and in those with IGT. In type 2 diabetic patients, a significant correlation was only noted when SiM was tested against Si(IVGTT) (P < or = 0.05). In most circumstances, the associations of Si(IVGTT) with Sib, SI2h and SiM were stronger than the corresponding associations with Ib, I2h or HOMA. SiM was the index that correlated best with Si(IVGTT) in the whole group (r = 0.92, P < 0.0001) as well as in NGT (r = 0.86, P < 0.0001), IGT (r = 0.96; P < 0.0001) and type 2 diabetes (r = 0.83, P < or = 0.05) subgroups. CONCLUSIONS: Calculations of sensitivity indexes from G and I concentrations in the basal state and during a conventional 2 h OGTT appear to be useful for coupling in the same simple and single test both a determination of glucose tolerance and an estimate of insulin sensitivity.     

Improvement in glucose tolerance as a result of enhanced insulin sensitivity during electroacupuncture in spontaneously diabetic Goto-Kakizaki rats

We studied whether electroacupuncture (EA) applied on the abdomen improved glucose tolerance in the Goto-Kakizaki (GK) rat, a genetic model of type 2 diabetes mellitus. Male GK rats and nondiabetic Wistar rats were studied under pentobarbital anesthesia. Blood samples were drawn from the ventral tail artery during the fasting stage and after a glucose load (0.5 g/kg). Electroacupuncture (15 Hz, 10 mA) was performed for 90 minutes during both the fasting and intravenous glucose tolerance test (IVGTT) periods. A hyperinsulinemic euglycemic clamp was also carried out to assess glucose uptake during EA. A significant decrease in fasting blood glucose and an increase in plasma insulin levels were observed during the fasting period in GK rats treated with EA. Blood glucose levels after glucose load were also significantly lower in GK rats treated with EA compared with controls. The homeostasis model assessment index during IVGTT indicated an improvement in insulin sensitivity in GK rats treated with EA, whereas glucose infusion rate during hyperinsulinemic clamp was increased significantly during EA. The present study demonstrated that EA improved hyperglycemia in the fasting stage with a marked increase in plasma insulin levels. Electroacupuncture also restored impaired glucose tolerance during an IVGTT in GK rats by enhancing insulin sensitivity.     

Single-nucleotide polymorphism rs7754840 of CDKAL1 is associated with impaired insulin secretion in nondiabetic offspring of type 2 diabetic subjects and in a large sample of men with normal glucose tolerance

CONTEXT: CDKAL1 is a recently discovered susceptibility gene for type 2 diabetes. OBJECTIVE: Our objective was to investigate the impact of rs7754840 of CDKAL1 on insulin secretion, insulin sensitivity, and risk of type 2 diabetes. DESIGN AND SETTINGS: Study 1 (the EUGENE2 study) was a cross-sectional study including subjects from five white populations in Europe (Denmark, Finland, Germany, Italy, and Sweden). Study 2 is an ongoing prospective study of Finnish men. PARTICIPANTS: In study 1, 846 nondiabetic offspring of type 2 diabetic patients (age 40 +/- 10 yr; body mass index 26.7 +/- 5.0 kg/m(2)) participated. In study 2, subjects included 3900 middle-aged men (533 type 2 diabetic and 3367 nondiabetic subjects). Interventions: Interventions included iv glucose-tolerance test (IVGTT), oral glucose-tolerance test (OGTT), and euglycemic-hyperinsulinemic clamp in study 1 and OGTT in study 2. MAIN OUTCOME MEASURES: Parameters of insulin secretion, insulin resistance, and glucose tolerance status were assessed. RESULTS: In study 1, carriers of the GC and CC genotypes of rs7754840 had 11 and 24% lower first-phase insulin release in an IVGTT compared with that in carriers of the GG genotype (P = 0.002). The C allele was also associated with higher glucose area under the curve in an OGTT (P = 0.016). In study 2, rs7754840 was significantly associated with type 2 diabetes (P = 0.022) and markers of impaired insulin release [insulinogenic index (IGI), P = 0.012] in 2405 men with normal glucose tolerance. CONCLUSIONS: rs7754840 of CDKAL1 was associated with markers of impaired insulin secretion in two independent studies. Furthermore, rs7754840 was associated with type 2 diabetes in Finnish men (study 2). Therefore, CDKAL1 is likely to increase the risk of type 2 diabetes by impairing insulin secretion.     

Insulin secretion and peripheral insulin sensitivity in obese children. Evidence of deficient glucose-stimulated early insulin release despite hyperinsulinemia.

Insulin secretion and peripheral insulin sensitivity were studied in 19 grossly-obese girls and 17 age-matched non-obese girls by means of the intravenous glucose tolerance test (IVGTT) and the simulated early insulin response test (SERT) respectively. SERT measures the fall in fasting blood glucose after a short infusion of insulin, performed so as to simulate the early phase of insulin release to the acute stimulus of an intravenous glucose load (ERex). In the IVGTT, the obese girls showed significantly increased early insulin response (ERend) in comparison with the non-obese girls. The glucose disappearance rate (KG) was similar in the two groups, although four obese girls had borderline low values. In the SERT, the rise in plasma insulin caused a much smaller decrease in blood glucose in the obese girls, than in the reference girls over the whole range of insulin levels studied. The relationship between insulin sensitivity and insulin secretion of each subject was evaluated from the plot of the ERex/ERend ratio vs blood glucose decrement. This showed that the hyperinsulinemia of the obese girls did not match the degree of peripheral resistance.     

TNF—α诱导的胰岛素抵抗小鼠胰岛素敏感性及糖脂代谢的变化

目的探讨TNF-α诱导的胰岛素抵抗（IR）小鼠胰岛素敏感性及糖脂代谢的变化。方法23只健康雄性C57BL／6J小鼠随机分为4组：高剂量（H）组、中剂量（M）组、低剂量（L）组分别给予腹腔注射6、3、1μg·kg^-1·d^-1的TNF-α，正常对照（NC）组注射等体积的生理盐水，共7天。采用静脉葡萄糖耐量试验（IVGTT）和3-[^3H]葡萄糖为示踪剂的扩展胰岛素钳夹技术，评价小鼠胰岛素敏感性和糖脂代谢的变化。结果TNF-α处理后，小鼠FBG、血浆胰岛素（Ins）和FFA水平均增高，且H组明显高于NC、M和L组。IVGTT结果显示H组糖耐量减低，Ins释放水平明显高于其他组。在胰岛素钳夹术中，H组基础葡萄糖清除率（GDR）和肝糖输出率（HGP）明显高于NC组（P＜50.01）。在钳夹稳态时，H组血浆Ins水平明显高于NC组（P＜0.01），Ins对FFA的抑制作用较NC组明显降低（P＜0.01），H组葡萄糖输注率（GIR）明显低于NC组（P＜0.01）；钳夹稳态时小鼠GDR明显增加，但H组GDR的增加仍明显低于NC组（P＜0.01）；钳夹结束时，NC组HGP被完全抑制，而H组仅被抑制59％。结论高剂量TNF-α（6μg·kg^-1·d^-1）处理可导致小鼠糖脂代谢紊乱以及肝和外周组织的球。     

Insulin secretion and insulin sensitivity in diabetic and non-diabetic subjects with hepatic nuclear factor-1alpha (maturity-onset diabetes of the young-3) mutations

OBJECTIVE: To evaluate insulin secretion and sensitivity in affected (diabetes mellitus or impaired glucose tolerance; n=7) and in unaffected (normal glucose tolerance; n=3) carriers of hepatocyte nuclear factor-1alpha (maturity-onset diabetes of the young-3 (MODY3)) gene mutations. METHODS: Insulin secretion was assessed by an i.v. glucose tolerance test (IVGTT), hyperglycemic clamp and arginine test, and insulin sensitivity by an euglycemic hyperinsulinemic clamp. Results were compared with those of diabetic MODY2 (glucokinase-deficient) and control subjects. RESULTS: The amount of insulin secreted during an IVGTT was decreased in affected MODY3 subjects (46+/-24 (s.d.) pmol/kg body weight (BW)) as compared with values in MODY2 (120+/-49pmol/kg BW) and control (173+/-37pmol/kg BW; P=0.0004) subjects. The amount of insulin secreted during a 10mmol/l glucose clamp was decreased in affected MODY3 subjects (171+/-78pmol/kg BW) and MODY2 subjects (302+/-104pmol/kg BW) as compared with control subjects (770+/-199pmol/kg BW; P=0.0001). Insulin secretion in response to arginine was decreased in affected MODY3 subjects. Milder and heterogeneous defects were observed in the unaffected MODY3 subjects; the amount of insulin secreted during the hyperglycemic clamp was 40-79% of that of controls. The response to arginine was abnormally delayed. Insulin sensitivity was decreased in diabetic but not in non-diabetic MODY3 subjects. CONCLUSIONS: Beta-cell dysfunction in response to glucose and arginine is observed in affected and unaffected MODY3 subjects. The MODY3 and MODY2 subtypes present different insulin secretion profiles. Secondary insulin resistance might contribute to the chronic hyperglycemia of MODY3 patients and modulate their glucose tolerance.     

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.     

利拉鲁肽对RNAi介导的脂联素基因抑制ApoE基因敲除小鼠糖脂代谢的影响

目的 探讨利拉鲁肽对脂联素基因表达缺陷的ApoE基因敲除(ApoE-/-)小鼠糖脂代谢的影响.方法 采用静脉葡萄糖耐量试验(IVGTT)评价利拉鲁肽的量效关系.利用扩展高胰岛素钳夹技术评价各组小鼠糖脂代谢和胰岛素敏感性变化.结果 在IVGTT中,利拉鲁肽1 mg/kg组,糖负荷后5、15和30 min血糖值均明显低于其它剂量组(均P＜0.01),而血浆胰岛素水平在5、15 min均明显高于其他3组(均P＜0.01).联合注射利拉鲁肽和脂联素RNAi腺病毒组体重、空腹血糖、血浆游离脂肪酸、总胆固醇、甘油三酯、血浆胰岛素和低密度脂蛋白胆固醇(LDL-C)水平显著低于脂联素RNAi腺病毒组(P＜0.05或P＜0.01),而高密度脂蛋白胆固醇(HDL-C)则明显高于脂联素RNAi组(P＜0.05).钳夹稳态时,脂联素RNAi组血浆胰岛素明显高于利拉鲁肽组(P＜0.01),游离脂肪酸、总胆固醇、甘油三酯虽被抑制,但仍明显高于利拉鲁肽组(P＜0.05).利拉鲁肽组葡萄糖输注率(GIR)则明显高于脂联素RNAi组(P＜0.01).钳夹结束时,脂联素RNAi组葡萄糖清除率(GRd)明显低于利拉鲁肽组(P＜0.01),而肝糖输出率则明显高于利拉鲁肽组(P＜0.01).结论 长期的利拉鲁肽干预上调了脂联素基因表达缺陷ApoE-/-小鼠血浆脂联素水平,并改善了其胰岛素抵抗.     

Estimates of insulin sensitivity from the intravenous-glucose-modified-clamp test depend on suppression of lipolysis in type 2 diabetes: a randomised controlled trial

Aims/hypothesis

The combined IVGTT–hyperinsulinaemic–euglycaemic clamp (Botnia clamp) allows the assessment of insulin secretion and sensitivity in one experiment. It remains unclear whether this clamp yields results comparable with those of the standard hyperinsulinaemic–euglycaemic clamp (SHEC) in diabetes patients. We hypothesised that the IVGTT induces responses affecting insulin sensitivity assessment.

Methods

Of 22 randomised diet- or metformin-treated patients with well-controlled type 2 diabetes, 19 randomly underwent a Botnia clamp and an SHEC, spaced by 2 weeks, in one clinical research centre in a crossover study. The main outcomes were whole-body and hepatic insulin sensitivity as measured by the clamp and [6,6-²H₂]glucose. Substrate utilisation was assessed from indirect calorimetry and beta cell function from insulin dynamics during IVGTT.

Results

The values of whole-body insulin sensitivity obtained from Botnia clamp and SHEC were correlated (r?=?0.87, p??1 min^?1 (Botnia and SHEC, p??1 min^?1 (p?NEFA (r?=??0.60, p?r?=??0.16, p?=?0.52) or hepatic insulin sensitivity between IVGTT and placebo before the clamps correlated with individual variations of insulin sensitivity.

Conclusions/interpretation

The Botnia clamp provides similar estimates of insulin sensitivity as SHEC in patients with type 2 diabetes, but changes in NEFA during IVGTT may affect insulin sensitivity and thereby the discrimination between insulin-sensitive and insulin-resistant individuals. Trial registration: ClinicalTrials.gov NCT01397279 Funding: The study was funded by the Ministry of Science and Research of the State of North Rhine-Westphalia and the German Federal Ministry of Health, and supported in part by grants from the Federal Ministry for Research to the Centers for Diabetes Research, Helmholtz Alliance Imaging and Curing Environmental Metabolic Diseases and the Schmutzler-Stiftung.     

The short insulin tolerance test for determination of insulin sensitivity: a comparison with the euglycaemic clamp.

The glucose clamp technique is currently regarded as the standard test for measuring insulin sensitivity against which other methods are compared but is unsuitable for routine screening of patients outside a hospital base. There is thus a need for a simpler test to measure insulin sensitivity. We have therefore compared the glucose disappearance rate KITT in the first 15 min of the insulin tolerance test (ITT) with the M and M/I values derived from the standard euglycaemic clamp in nine normal subjects and eight subjects with Type 2 (non-insulin dependent) diabetes mellitus and coexisting obesity. All subjects underwent the ITT and euglycaemic clamp in random order. Nine subjects later had a repeat ITT to determine the reproducibility of the test. In the ITT, 0.1 U kg-1 body weight, human Actrapid insulin was given as an IV bolus and simultaneous arterialized and venous blood samples were obtained every minute for 15 min. The first order rate constant for the disappearance of glucose KITT over the period 3-15 min was taken as a measure of insulin sensitivity. The euglycaemic clamp was performed with an insulin infusion of 50 mU kg-1 h-1 for 120 min and a variable rate glucose infusion to maintain blood glucose concentration at 0.5 mmol l-1 below fasting level to minimize the effect of endogenous insulin secretion. The ratio of the mean rate of glucose infused (M, mumol kg-1 min-1) to the plasma insulin over the last 30 min of the clamp was taken as a measure of tissue sensitivity to insulin (M/I) assuming endogenous glucose output was suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intravenous glucose tolerance test-derived insulin sensitivity changes during the menstrual cycle

Using glucose tolerance tests or a glucose clamp some studies report impaired insulin sensitivity during the luteal phase of the menstrual cycle, while others find no change in insulin sensitivity. Tissue sensitivity to insulin and glucose effectiveness can be estimated using the minimal model analysis of an iv glucose tolerance test (IVGTT), but this method has never been applied to evaluate the impact of the menstrual cycle on these parameters. We, therefore, studied eight cycling women using tolbutamide-modified IVGTTs during three different phases of the same menstrual cycle: early follicular, midcycle, and midluteal. Insulin sensitivity (SI) and glucose effectiveness were derived using insulin and glucose levels obtained from tolbutamide-modified IVGTTs and analyzed with the minimal model computer program. The mean SI (x10(-4)/min.microU/mL) decreased in a stepwise fashion from the follicular level of 6.20 +/- 0.91 to a midcycle level of 4.95 +/- 0.73 and was lowest in the luteal phase (3.20 +/- 0.25; P less than 0.007). No change in glucose effectiveness occurred as a function of the menstrual cycle. These findings indicate a significant decrease in insulin sensitivity in the luteal phase of the normal menstrual cycle, but no significant change at midcycle.     

Physiologic modeling of the intravenous glucose tolerance test in type 2 diabetes: a new approach to the insulin compartment

The minimal model of Bergman et al has been used to yield estimates of insulin sensitivity (Si) and glucose effectiveness (Sg) in type 2 diabetes by incorporating exogenous insulin protocols into the regular intravenous glucose tolerance test (IVGTT). These estimates, however, are influenced by the degree to which the dose of exogenous insulin is greater than the physiologic response to a glucose load. Moreover, most studies have related to type 2 diabetes subjects whose diabetes was relatively mild in terms of therapeutic requirements. To develop a "minimal disturbance" approach in estimating Si and Sg in type 2 diabetes, we have used a reduced glucose load (200 mg/kg) and a "physiologic" insulin infusion throughout the IVGTT in a series of 8 patients, 5 of whom were insulin-requiring. Data from this approach were analyzed using the modelling program CONSAM to apply the Bergman model, either unmodified (BMM), or incorporating an additional delay element between the plasma and "remote" insulin compartments (MMD). Application of the MMD and extension of the IVGTT from 3 to 5 hours improved successful resolution of Si and Sg from 37.5% (BMM, 3-hour IVGTT) to 100% (MMD, 5-hour IVGTT). Si was reduced in these type 2 diabetes patients compared with normal subjects (1.86 +/- 0.60 v. 8.65 +/- 2.27 min(-1) x microU(-1) x mL x 10(4) P <.01). The results were validated in the type 2 diabetes group using a 2-stage euglycemic clamp ((Si)CLAMP = 2.02 +/- 0.42 min(-1) x microU(-1) x mL x 10(4) P >.4). Sg was not significantly reduced (2.00 +/- 0.25 type 2 diabetes v. 1.55 +/- 0.26 normal min(-1) x 10(2)). Data from a group of normal nondiabetic subjects was then analyzed using the MMD, but this approach did not enhance the fit of the model compared with the BMM. This result indicates that the delay in insulin action in type 2 diabetes represents an abnormality whereby the onset of insulin action cannot be described as a single phase in the transfer of insulin from plasma to the remote compartment. It is postulated that the physiologic basis for this delayed action may relate to transcapillary endothelial transfer of insulin, this process limiting the rate of onset of insulin action.     

The Leu7Pro polymorphism of the neuropeptide Y gene regulates free fatty acid metabolism

The Leu7Pro polymorphism in the signal peptide of the preproneuropeptide Y (NPY) has been associated with dyslipidemias and free fatty acid (FFA) levels during exercise. The association of this polymorphism with insulin sensitivity has not been studied. In this study, the Leu7Pro polymorphism was determined in 2 groups of nondiabetic middle-aged subjects (n [equals] 266 and n [equals] 295). Insulin sensitivity was measured with the hyperinsulinemic euglycemic clamp (n [equals] 266) or with an intravenous glucose tolerance test (IVGTT, n [equals] 295). First-phase insulin secretion was determined as insulin area under the curve (AUC) during the first 10 minutes of the IVGTT. FFAs were measured both in the fasting state and during the hyperinsulinemic clamp. The Leu7Pro polymorphism of the NPY gene was not associated with the rates of whole body glucose uptake, insulin sensitivity index, insulin secretion during the IVGTT, or insulin AUC during the oral glucose tolerance test. However, the Pro7 allele was associated with low FFA levels both in the fasting state (P [equals] .043) and during the hyperinsulinemic clamp (P [equals] .003). In conclusion, the Leu7Pro polymorphism of the NPY gene associates with alterations in FFA metabolism but does not have an impact on insulin sensitivity, insulin secretion, or glucose metabolism. [copy ] 2003 Elsevier Inc. All rights reserved.     

Early impairment of insulin secretion in rats after surgical trauma

OBJECTIVE: Hyperglycaemia associated with insulin resistance is common after trauma and surgical procedures. Both reduced insulin sensitivity and altered insulin secretion may contribute to the impaired glucose homeostasis. We have demonstrated that skeletal muscle insulin resistance is present 2 h after small intestinal resection in rats. In this study, the aim was to investigate insulin secretion in the same experimental model. DESIGN: Small intestinal resection (5 cm) was performed in adult rats. The control animals underwent anaesthesia only. METHODS: The intravenous glucose tolerance test (IVGTT), the hyperglycaemic clamp and in vitro studies in isolated pancreatic islets were performed after surgery. Concentrations of blood glucose, plasma insulin, corticosterone and interleukin-6 (IL-6) were determined 0-5 h postoperatively. RESULTS: The insulin response in the IVGTT was attenuated 2 h (P<0.05) but not 4 h or during the hyperglycaemic clamp (3.5-4.5 h) postoperatively. Insulin secretion in response to glucose in vitro was decreased 2 h after the surgery (P<0.05), but no change was seen in arginine-stimulated secretion. Plasma levels of corticosterone were increased 3.5-5 h postoperatively (P<0.001-0.05). Increases in IL-6 were also seen postoperatively. CONCLUSION: We demonstrate that glucose-induced, but not arginine-induced, insulin secretion is temporarily impaired after intestinal resection in rats. The later appearance of elevated corticosterone and IL-6 levels, as well as the preservation of the beta-cell inhibition in vitro, argues against the possibility that these two circulating factors are causally responsible for reduced insulin release seen after surgery in this model.     

Interaction between glucose metabolism and endogenous insulin release in hypertension

The minimal model approach was applied to examine the dynamic interaction between glucose metabolism and endogenous insulin release during an intravenous glucose tolerance test (IVGTT) in a group of hypertensive patients (H group) compared with a group of normotensive subjects (N group). A modified version of the classical minimal model of C-peptide kinetics and secretion was used to evaluate the total amount of insulin secretion per unit of distribution volume (TIS) together with 3 indexes of beta-cell function (the basal, Phi(b), first, Phi1, and second phase, Phi2, beta-cell sensitivity to glucose). These indexes were associated with estimates of glucose effectiveness (S(G)) and insulin sensitivity (S(I)) provided by the classical minimal model of glucose kinetics. No significant differences were found in Phi(b), Phi1, and Phi2 estimates between the H group and the N group. In the H group, the average TIS was 54% higher (P <.05) than in the N group, while S(G) and S(I) estimates showed a 44% decrease (P <.05) and a 51% decrease (P <.05), respectively. These results suggest that hyperglycemia observed in our H group during IVGTT is a compensatory response to insulin resistance (low S(I)) and to the reduced ability of glucose to promote its own metabolism (low S(G)). This hyperglycemic state causes a larger than normal stimulation of beta cell, which explains insulin hypersecretion (higher TIS) even in the presence of normal beta-cell sensitivity values of Phi(b), Phi1, and Phi2.     

Exenatide 对高脂诱导胰岛素抵抗大鼠胰岛素敏感性及糖脂代谢的影响

目的 探讨Exenatide对高脂诱导胰岛素抵抗大鼠胰岛β细胞功能、胰岛素敏感性及糖脂代谢的影响. 方法 高脂诱导胰岛素抵抗大鼠给予Exenatide 6周后,采用静脉葡萄糖耐量(IVGTT)和胰岛素耐量(ITT)试验以及扩展胰岛素钳夹技术测定胰岛素敏感性和糖脂代谢,并观察血浆脂联素水平的变化.结果 高脂大鼠(HF)经Exenatide处理后,Lee′s指数、空腹血浆游离脂肪酸(FFA)、甘油三酯、胆固醇明显降低(均P＜0.01);IVGTT和ITT明显改善,胰岛素分泌水平增高,高剂量组(HFH)较低剂量组(HFL)上述指标改善更为明显.同时,HFH组血浆脂联素水平也明显升高(P＜0.01).在钳夹稳态时,HF组与对照组(NC)相比,血浆FFA、胰岛素水平均明显升高(均P＜0.01),葡萄糖输注率(GIR)、葡萄糖清除率(GRd)明显降低(均P＜0.01),且胰岛素对肝糖输出(HGP)的抑制作用明显障碍(仅抑制26%).经Exenatide(2 μg/kg)处理以后,血浆FFA、胰岛素水平则明显降低(均P＜0.01),GRd、GIR明显升高(均P＜0.01),胰岛素对HGP的抑制作用明显增强(抑制72%).结论 对高脂喂养大鼠用Exenatide预处理可能通过促进β细胞胰岛素分泌和上调血浆脂联素水平,改善糖脂代谢而使机体胰岛素敏感性增加.