Pathogenesis of pre-diabetes: mechanisms of fasting and postprandial hyperglycemia in people with impaired fasting glucose and/or impaired glucose tolerance

Thirty-two subjects with impaired fasting glucose (IFG) and 28 subjects with normal fasting glucose (NFG) ingested a labeled meal and 75 g glucose (oral glucose tolerance test) on separate occasions. Fasting glucose, insulin, and C-peptide were higher (P < 0.05) in subjects with IFG than in those with NFG, whereas endogenous glucose production (EGP) did not differ, indicating hepatic insulin resistance. EGP was promptly suppressed, and meal glucose appearance comparably increased following meal ingestion in both groups. In contrast, glucose disappearance (R(d)) immediately after meal ingestion was lower (P < 0.001) in subjects with IFG/impaired glucose tolerance (IGT) and IFG/diabetes but did not differ in subjects with IFG/normal glucose tolerance (NGT) or NFG/NGT. Net insulin action (S(i)) and insulin-stimulated glucose disposal (S(i)*) were reduced (P < 0.001, ANOVA) in subjects with NFG/IGT, IFG/IGT, and IFG/diabetes but did not differ in subjects with NFG/NGT or IFG/NGT. Defective insulin secretion also contributed to lower postprandial R(d) since disposition indexes were lower (P < 0.001, ANOVA) in subjects with NFG/IGT, IFG/IGT, and IFG/diabetes but did not differ in subjects with NFG/NGT and IFG/NGT. We conclude that postprandial hyperglycemia in individuals with early diabetes is due to lower rates of glucose disappearance rather than increased meal appearance or impaired suppression of EGP, regardless of their fasting glucose. In contrast, insulin secretion, action, and the pattern of postprandial turnover are essentially normal in individuals with isolated IFG.     

Mechanisms of the age-associated deterioration in glucose tolerance: contribution of alterations in insulin secretion,action, and clearance

Glucose tolerance decreases with age. For determining the cause of this decrease, 67 elderly and 21 young (70.1 +/- 0.7 vs. 23.7 +/- 0.8 years) participants ingested a mixed meal and received an intravenous injection of glucose. Fasting glucose and the glycemic response above basal were higher in the elderly than in the young participants after either meal ingestion (P < 0.001) or glucose injection (P < 0.01). Insulin action (Si), measured with the meal and intravenous glucose tolerance test models, was highly correlated (r = 0.72; P < 0.001) and lower (P 相似文献   

Effects of age and sex on postprandial glucose metabolism: differences in glucose turnover, insulin secretion, insulin action, and hepatic insulin extraction

To determine the effects of age and sex on the regulation of postprandial glucose metabolism, glucose turnover, insulin secretion, insulin action, and hepatic insulin extraction were concurrently measured in 145 healthy elderly (aged 70 +/- 1 years) and in 58 young (aged 28 +/- 1 years) men and women before and after ingestion of a mixed meal containing [1-(13)C]glucose. At the time of meal ingestion, [6-(3)H]glucose and [6,6-(2)H(2)]glucose were infused intravenously to enable concurrent measurement of the rates of postprandial endogenous glucose production (EGP), meal appearance, and glucose disappearance. Fasting and postprandial glucose concentrations were higher (P < 0.001) in both elderly women and elderly men compared with young individuals of the same sex. The higher postprandial glucose concentrations in the elderly than young women were caused by higher rates of meal appearance (P < 0.01) and slightly lower (P < 0.05) rates of glucose disappearance immediately after eating. In contrast, higher glucose concentrations in the elderly than young men were solely due to decreased (P < 0.001) glucose disappearance. Although postprandial glucose concentrations did not differ in elderly women and elderly men, rates of meal appearance and glucose disappearance rates both were higher (P < 0.001) in the women. Fasting EGP was higher (P < 0.05) in elderly than young subjects of both sexes and in women than men regardless of age. On the other hand, postprandial suppression of EGP was rapid all groups. Insulin action and secretion were lower (P < 0.001) in the elderly than young men but did not differ in the elderly and young women. This resulted in lower (P < 0.001) meal disposition indexes in elderly than young men but no difference in elderly and young women. Total meal disposition indexes were lower (P < 0.05) in elderly men than elderly women, indicating impaired insulin secretion, whereas disposition indexes were higher (P < 0.05) in young men than young women. Hepatic insulin clearance was greater (P < 0.001) in the elderly than young subjects of both sexes but did not differ between men and women regardless of age. In contrast, the ability of glucose to facilitate its own uptake (glucose effectiveness) was higher (P < 0.001) in women than men but did not differ in elderly and young subjects. Thus, age and sex impact on insulin secretion, insulin action, hepatic insulin extraction, and glucose effectiveness, resulting in substantial differences in the regulation of postprandial glucose metabolism in men and women and in elderly and young subjects.     

Two years of treatment with dehydroepiandrosterone does not improve insulin secretion, insulin action, or postprandial glucose turnover in elderly men or women

To determine if dehydroepiandrosterone (DHEA) replacement improves insulin secretion, insulin action, and/or postprandial glucose metabolism, 112 elderly subjects with relative DHEA deficiency ingested a labeled mixed meal and underwent a frequently sampled intravenous glucose tolerance test before and after 2 years of either DHEA or placebo. Despite restoring DHEA sulphate concentrations to values observed in young men and women, the changes over time in fasting and postprandial glucose concentrations, meal appearance, glucose disposal, and endogenous glucose production were identical to those observed after 2 years of placebo. The change over time in postmeal and intravenous glucose tolerance test insulin and C-peptide concentrations did not differ in men treated with DHEA or placebo. In contrast, postmeal and intravenous glucose tolerance test change over time in insulin and C-peptide concentrations were greater (P < 0.05) in women after DHEA than after placebo. However, since DHEA tended to decrease insulin action, the change over time in disposition indexes did not differ between DHEA- and placebo-treated women, indicating that the slight increase in insulin secretion was a compensatory response to a slight decrease in insulin action. We conclude that 2 years of replacement of DHEA in elderly men and women does not improve insulin secretion, insulin action, or the pattern of postprandial glucose metabolism.     

Insulin secretion and insulin sensitivity in relation to glucose tolerance: lessons from the Botnia Study

Recently, a new stage in glucose tolerance, impaired fasting glucose (IFG) (fasting plasma glucose level of 6.1-6.9 mmol/l), was introduced in addition to impaired glucose tolerance (IGT) (2-h glucose level of 7.8-11.0 mmol/l). It is not clear whether IFG and IGT differ with respect to insulin secretion or sensitivity. To address this question, we estimated insulin secretion (by measuring both insulin levels and the ratio of insulin-to-glucose levels in 30-min intervals) and insulin sensitivity (by using the homeostasis model assessment [HOMA] index) from an oral glucose tolerance test (OGTT) in 5,396 individuals from the Botnia Study who had varying degrees of glucose tolerance. There was poor concordance between IFG and IGT: only 36% (303 of 840) of the subjects with IFG had IGT, whereas 62% (493 of 796) of the subjects with IGT did not have IFG. Compared with subjects with normal glucose tolerance (NGT), subjects with IFG were more insulin resistant (HOMA-insulin resistance [IR] values 2.64 +/- 0.08 vs. 1.73 +/- 0.03, P < 0.0005), had greater insulin responses during an OGTT (P = 0.0001), had higher waist-to-hip ratios (P < 0.005), had higher triglyceride and total cholesterol concentrations (P < 0.0005), and had lower HDL cholesterol concentrations (P = 0.0001). Compared with subjects with IFG, subjects with IGT had a lower incremental 30-min insulin-to-glucose area during an OGTT (13.8 +/- 1.7 vs. 21.7 +/- 1.7, P = 0.0008). Compared with subjects with IGT, subjects with mild diabetes (fasting plasma glucose levels <7.8 mmol/l) showed markedly impaired insulin secretion that could no longer compensate for IR and elevated glucose levels. A progressive decline in insulin sensitivity was observed when moving from NGT to IGT and to subjects with diabetes (P < 0.05 for trend), whereas insulin secretion followed an inverted U-shaped form. We conclude that IFG is characterized by basal IR and other features of the metabolic syndrome, whereas subjects with IGT have impaired insulin secretion in relation to glucose concentrations. An absolute decompensation of beta-cell function characterizes the transition from IGT to mild diabetes.     

Dichotomy between postprandial glucose and lipid profiles in adults with cystic fibrosis: A pilot study

BackgroundCystic fibrosis (CF) patients present a high incidence of glucose tolerance abnormalities. Altered insulin secretion combined with recommended high-fat intake could be associated with dysregulation of glucose and lipid metabolism. We examined postprandial glucose and lipid profiles during an oral glucose tolerance test (OGTT) and following a standardized high-fat test meal (TM).MethodsSixteen CF patients with normal glucose tolerance (NGT) or CF-related diabetes (CFRD) and 16 controls underwent a 4 h OGTT and a TM. We then measured plasma glucose, insulin, free fatty acid (FFA) and triglyceride (TG) concentrations.ResultsCF patients presented higher glucose excursion compared to controls after the OGTT and TM. However, in CF patients, this excursion was significantly reduced in both amplitude and length after the TM. The TM provoked a comparable increase in TG levels in both groups whereas they remained stable during the OGTT. FFAs were suppressed similarly in both groups after both challenges.ConclusionCF is associated with abnormal glucose excursion in the presence of relatively normal lipid excursion. The rapid normalization of glucose values after a mixed meal should be further explored and, if confirmed, might have significant implications for CFRD diagnostic.     

Banting lecture 1990. Beta-cells in type II diabetes mellitus

In 1960, immunoassays of insulin first demonstrated significant quantities of circulating hormone in non-insulin-dependent (type II) diabetes and for 30 yr have fostered debate as to whether a beta-cell abnormality plays an etiological role in this syndrome. Early efforts to determine the adequacy of islet beta-cell function showed that obesity and its associated insulin resistance were major confounding variables. Subsequently, it was recognized that glucose not only directly regulated insulin synthesis and secretion but moderated all other islet signals, including other substrates, hormones, and neural factors. When both obesity and glucose are taken into account, it becomes clear that patients with fasting hyperglycemia all have abnormal islet function. Type II diabetes is characterized by a defect in first-phase or acute glucose-induced insulin secretion and a deficiency in the ability of glucose to potentiate other islet nonglucose beta-cell secretagogues. The resulting hyperglycemia compensates for the defective glucose potentiation and maintains nearly normal basal insulin levels and insulin responses to nonglucose secretagogues but does not correct the defect in first-phase glucose-induced insulin release. Before the development of fasting hyperglycemia, only first-phase glucose-induced insulin secretion is obviously defective. This is because progressive islet failure is matched by rising glucose levels to maintain basal and second-phase insulin output. The relationship between islet function and fasting plasma glucose is steeply curvilinear, so that there is a 75% loss of beta-cell function by the time the diagnostic level of 140 mg/dl is exceeded. This new steady state is characterized by glucose overproduction and inefficient utilization. Insulin resistance is also present in most patients and contributes to the hyperglycemia by augmenting the glucose levels needed for compensation. Decompensation and absolute hypoinsulinemia occur when the renal threshold for glucose is exceeded and prevents further elevation of circulating glucose. The etiology of the islet beta-cell lesion is not known, but a hypothesis based on basal hyperproinsulinemia and islet amyloid deposits in the pancreas of type II diabetes is reviewed. The recent discovery of the islet amyloid polypeptide (IAPP) or amylin, which is the major constituent of islet amyloid deposits, is integrated into this hypothesis. It is suggested that pro-IAPP and proinsulin processing and mature peptide secretion normally occur together and that abnormal processing, secondary to or in conjunction with defects in hormone secretion, lead to progressive accumulation of intracellular IAPP and pro-IAPP, which in cats, monkeys, and humans form intracellular fibrils and amyloid deposits with a loss of beta-cell mass.(ABSTRACT TRUNCATED AT 400 WORDS)     

Quantification of insulin secretion in relation to insulin sensitivity in nondiabetic postmenopausal women

To evaluate mechanisms underlying the close association between insulin secretion and insulin sensitivity, insulin sensitivity was evaluated by the euglycemic-hyperinsulinemic clamp technique (M/I(clamp)) and insulin secretion was determined from the 75-g oral glucose tolerance test (OGTT) and from the glucose-dependent arginine-stimulation test in 81 nondiabetic postmenopausal women, all aged 61 years. M/I(clamp) was normally distributed with mean +/- SD of 69.9 +/- 30.5 nmol glucose center.kg(-1).min(-1)/pmol insulin.l(-1). It was found that the several different measures of insulin secretion from the OGTT and the glucose-dependent arginine-stimulation test were all inversely related to M/I(clamp). However, measures determining the direct insulin responses were more markedly potentiated by low M/I(clamp) than were measures determining glucose potentiation of insulin secretion. Moreover, the product of M/I(clamp) times measures of insulin secretion (disposition index [DI]) was inversely related to the 2-h glucose value. Finally, surrogate insulin sensitivity measures quantified from OGTT and the glucose-dependent arginine-stimulation test only weakly correlated to M/I(clamp) (R(2) approx equal to 0.25). Thus, 1) insulin secretion is adaptively increased when insulin sensitivity is low in nondiabetic postmenopausal women; 2) beta-cell exocytotic ability shows more efficient adaptation than beta-cell glucose recognition to low insulin sensitivity; 3) impaired beta-cell adaptation (i.e., low DI) is associated with higher 2-h glucose values during OGTT, although other regulatory mechanisms also exist; and 4) indirect surrogate measures of insulin sensitivity only weakly correlate to insulin sensitivity as determined by the euglycemic-hyperinsulinemic clamp.     

Two-hour seven-sample oral glucose tolerance test and meal protocol: minimal model assessment of beta-cell responsivity and insulin sensitivity in nondiabetic individuals

Highly informative yet simple protocols to assess insulin secretion and action would considerably enhance the quality of epidemiological and large-scale clinical trials. In an effort to develop such protocols, a 5-h, 11-sample oral glucose tolerance test (OGTT) was performed in 100 individuals and a 7-h, 21-sample meal in another 100. Plasma glucose, insulin, and C-peptide concentrations were measured. We show that virtually the same minimal model assessment of beta-cell responsivity (dynamic [Phi(d)] and static [Phi(s)]), insulin sensitivity (Si), and disposition index (DI) can be obtained with a reduced seven-sample 2-h protocol: Phi(d), reduced versus full: 871.50 vs. 873.32, r = 0.98 in OGTT and 494.88 vs. 477.99 10(-9), r = 0.91 in meal; Phi(s): 42.36 vs. 44.35, r = 0.88 in OGTT and 35.31 vs. 35.37 10(-9) min(-1), r = 0.90 in meal; Si: 24.33 vs. 22.77 10(-5) dl x kg(-1) x min(-1) per pmol/l, r = 0.89 in OGTT and 19.03 vs. 19.77 10(-5) dl x kg(-1) x min(-1) per pmol/l, r = 0.85 in meal; and DI: 1,282.26 vs. 1,273.23, r = 0.84 in OGTT and 726.92 vs. 776.97 10(-14) dl . kg(-1) x min(-2) per pmol/l, r = 0.84 in meal. This reduced protocol will facilitate the study of insulin secretion and action under physiological conditions in nondiabetic humans.     

Insulin secretion and action in subjects with impaired fasting glucose and impaired glucose tolerance: results from the Veterans Administration Genetic Epidemiology Study

This study was conducted to observe changes in insulin secretion and insulin action in subjects with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT). A total of 319 subjects were studied with an oral glucose tolerance test (OGTT). Fasting plasma glucose and insulin concentrations were measured at baseline and every 30 min during the OGTT. Fifty-eight subjects also received a euglycemic-hyperinsulinemic clamp. Insulin sensitivity was calculated as the total glucose disposal (TGD) during the last 30 min of the clamp. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated from fasting plasma glucose and insulin concentrations. Subjects with IFG had TGD similar to normal glucose-tolerant subjects, while subjects with IGT and combined IFG/IGT had significantly reduced TGD. HOMA-IR in subjects with IFG was similar to that in subjects with combined IFG/IGT and significantly higher than HOMA-IR in subjects with IGT or NGT. Insulin secretion, measured by the insulinogenic index (DeltaI(0-30)/DeltaG(0-30)) and by the ratio of the incremental area under the curve (AUC) of insulin to the incremental AUC of glucose (0-120 min), was reduced to the same extent in all three glucose-intolerant groups. When both measurements of beta-cell function were adjusted for severity of insulin resistance, subjects with IGT and combined IFG/IGT had a significantly greater reduction in insulin secretion than subjects with IFG. Subjects with IGT and IFG have different metabolic characteristics. Differences in insulin sensitivity and insulin secretion may predict different rates of progression to type 2 diabetes and varying susceptibility to cardiovascular disease.     

The impact of impaired insulin release and insulin resistance on glucose intolerance after renal transplantation

The current knowledge of the pathogenesis of post-transplant glucose intolerance is sparse. This study was undertaken to assess the relative importance of insulin secretion (ISec) and insulin sensitivity (IS) in the pathogenesis of post-transplant diabetes mellitus (PTDM), impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) after renal transplantation. An oral glucose tolerance test (OGTT) was performed in 167 non-diabetic recipients 10 wk after renal transplantation. Fasting, 1-h and 2-h insulin and glucose levels were used to estimate the insulin secretory response and IS. One year after transplantation 89 patients were re-examined with an OGTT including measurements of fasting and 2 h glucose. Ten weeks after transplantation the PTDM-patients had significantly lower ISec and IS than patients with IGT/IFG, who again had lower ISec and IS than those with normal glucose tolerance (NGT). One year later, a similar difference in baseline ISec was observed between the three groups, whereas baseline IS did not differ significantly. Patients who improved their glucose tolerance during the first year, were mainly characterized by a significantly greater baseline ISec, and they received a significantly higher median prednisolone dose at baseline with a subsequent larger dose reduction during the first year, than the patients who had their glucose tolerance unchanged or worsened. In conclusion, both impaired ISec and IS characterize patients with PTDM and IGT/IFG in the early course after renal transplantation. The presence of defects in insulin release, rather than insulin action, indicates a poor prognosis regarding later normalization of glucose tolerance.     

Early differential defects of insulin secretion and action in 19-year-old caucasian men who had low birth weight

Several studies have linked low birth weight (LBW) and type 2 diabetes. We investigated hepatic and peripheral insulin action including intracellular glucose metabolism in 40 19-year-old men (20 LBW, 20 matched control subjects), using the hyperinsulinemic-euglycemic clamp technique at two physiological insulin levels (10 and 40 mU/m(2) per min), indirect calorimetry, and [3-(3)H]glucose. Insulin secretion was examined during an oral and intravenous glucose tolerance test. Fasting p-glucose was higher in the LBW group (5.6 +/- 0.1 vs. 5.4 +/- 0.1; P < 0.05). Basal plasma glycerol concentrations were significantly lower in the LBW group. Insulin-stimulated glycolytic flux was significantly reduced, and suppression of endogenous glucose production was enhanced in the LBW group. Nevertheless, basal and insulin-stimulated rates of whole-body peripheral glucose disposal, glucose oxidation, lipid oxidation, exogenous glucose storage, and nonoxidative glucose metabolism were similar in the two groups. Insulin secretion was reduced by 30% in the LBW group, when expressed relative to insulin sensitivity (disposition index = insulin secretion x insulin action). We propose that reduced insulin-stimulated glycolysis precedes overt insulin resistance in LBW men. A lower insulin secretion may contribute to impaired glucose tolerance and ultimately lead to diabetes.     

Quantification of insulin secretion and in vivo insulin action in nonobese and moderately obese individuals with normal glucose tolerance

Insulin secretion and in vivo insulin action were quantified in nonobese and moderately obese subjects (approximately 35% above desirable body weight) with normal glucose tolerance. Insulin secretion was estimated by determining plasma insulin responses to a 75-g oral challenge, and in vivo insulin-stimulated glucose uptake by the euglycemic clamp technique. Plasma glucose levels of the two groups were identical during the glucose tolerance test, but the plasma insulin response was significantly greater (P less than 0.01) in the obese subjects. However, insulin-stimulated glucose utilization by the two groups was equal during the euglycemic clamp studies. These results were supported by the fact that degree of obesity correlated significantly with insulin response (r = 0.61, P less than 0.005), but not with insulin-stimulated glucose utilization (r = -0.25, P greater than 0.2). Thus, indirect evidence that moderately obese subjects were more insulin-resistant based on measurement of plasma insulin response was not supported by direct quantification of insulin action. One explanation for these findings is that the height of the plasma insulin response bears no relationship to loss of in vivo insulin action, but that seems unlikely in view of the fact that there was a significant correlation (r = -0.52, P less than 0.01) between these two variables in the group as a whole. Therefore, it appears that the hyperinsulinemia seen in obese individuals may not be a simple function of insulin resistance, and that ability of insulin to stimulate glucose utilization is not significantly impaired in moderately obese subjects with normal glucose tolerance. Alternatively, the degree of impairment in insulin action seen in these individuals is insufficient to be detected by the euglycemic clamp technique.     

Insulin action and insulin secretion in identical twins with MODY. Evidence for defects in both insulin action and secretion

To evaluate the pathogenetic mechanisms responsible for development of diabetes in the genetically inherited disease maturity-onset diabetes of the young (MODY), we have investigated a pair of identical twins (19 yr old) from a MODY family. One twin had nondiabetic fasting plasma glucose values but impaired glucose tolerance (IGT), whereas the other suffered from frank diabetes (fasting plasma glucose 12.5 mM). Differences in insulin secretion pattern and/or insulin action between the twins is supposed to be responsible for development of hyperglycemia in MODY. On the other hand, identical defects in insulin secretion and action in the twins may point to the primary genetic defect in MODY. Therefore, our aim was to investigate insulin secretion and insulin action in the twins to find these differences and similarities. We found that fasting plasma insulin and C-peptide values were slightly increased in the twins, whereas the responses of insulin and C-peptide to oral glucose tolerance tests (OGTT) and meals were similar in the twins and within normal range. The insulin responses to OGTT were, however, lower than expected from the glucose values, indicating a beta-cell defect. Despite elevated plasma insulin levels, basal hepatic glucose output (HGO) was normal in the IGT twin but increased by 75% in the diabetic twin. The maximally inhibitory effect of insulin on HGO, when estimated at euglycemia, was normal in the IGT twin but reduced by 60% in the diabetic twin. Furthermore, the maximal insulin-mediated glucose uptake in peripheral tissues was reduced by 40% in the diabetic twin.(ABSTRACT TRUNCATED AT 250 WORDS)     

The prevalent Glu23Lys polymorphism in the potassium inward rectifier 6.2 (KIR6.2) gene is associated with impaired glucagon suppression in response to hyperglycemia

Genetic factors play an important role in the pathogenesis of type 2 diabetes. The relevance to type 2 diabetes of the common polymorphism Glu23Lys in the potassium inward rectifier 6.2 (KIR6.2) gene is still controversial. The aim of this study was to assess whether this polymorphism influences beta-cell function, alpha-cell function, or insulin action. We therefore studied 298 nondiabetic subjects using an oral glucose tolerance test (OGTT) and 75 nondiabetic subjects using a hyperglycemic clamp (10 mmol/l) with additional glucagon-like peptide (GLP)-1 and arginine stimulation. The prevalence of the Lys allele was approximately 37%, and the Lys allele was associated with higher incremental plasma glucose during the OGTT (P = 0.03, ANOVA). Neither first- nor second-phase glucose-stimulated C-peptide secretion was affected by the presence of the polymorphism; nor were maximal glucose-, GLP-1-, or arginine-induced C-peptide secretion rates; nor was insulin sensitivity (all P > 0.7). However, the relative decrease in plasma glucagon concentrations during the 10 min after the glucose challenge was reduced in carriers of the Lys allele (10 +/- 3% decrease from baseline in Lys/Lys, 18 +/- 2% in Glu/Lys, and 20 +/- 2% in Glu/Glu; P = 0.01, ANOVA). In conclusion, our findings suggest that the common Glu23Lys polymorphism in KIR6.2 is not necessarily associated with beta-cell dysfunction or insulin resistance but with diminished suppression of glucagon secretion in response to hyperglycemia. Our findings thus confirm its functional relevance for glucose metabolism in humans.     

Effects of glucosamine infusion on insulin secretion and insulin action in humans

Glucose toxicity (i.e., glucose-induced reduction in insulin secretion and action) may be mediated by an increased flux through the hexosamine-phosphate pathway. Glucosamine (GlcN) is widely used to accelerate the hexosamine pathway flux, independently of glucose. We tested the hypothesis that GlcN can affect insulin secretion and/or action in humans. In 10 healthy subjects, we sequentially performed an intravenous glucose (plus [2-3H]glucose) tolerance test (IVGTT) and a euglycemic insulin clamp during either a saline infusion or a low (1.6 micromol x min(-1) x kg(-1)) or high (5 micromol x min(-1) x kg(-1) [n = 5]) GlcN infusion. Beta-cell secretion, insulin (SI*-IVGTT), and glucose (SG*) action on glucose utilization during the IVGTT were measured according to minimal models of insulin secretion and action. Infusion of GlcN did not affect readily releasable insulin levels, glucose-stimulated insulin secretion (GSIS), or the time constant of secretion, but it increased both the glucose threshold of GSIS (delta approximately 0.5-0.8 mmol/l, P < 0.03-0.01) and plasma fasting glucose levels (delta approximately 0.3-0.5 mmol/l, P < 0.05-0.02). GlcN did not change glucose utilization or intracellular metabolism (glucose oxidation and glucose storage were measured by indirect calorimetry) during the clamp. However, high levels of GlcN caused a decrease in SI*-IVGTT (delta approximately 30%, P < 0.02) and in SG* (delta approximately 40%, P < 0.05). Thus, in humans, acute GlcN infusion recapitulates some metabolic features of human diabetes. It remains to be determined whether acceleration of the hexosamine pathway can cause insulin resistance at euglycemia in humans.     

Postoperative oral glucose tolerance and stimulated insulin secretion: a predictor of endocrine graft function more than 10 years after pancreas-kidney transplantation

BACKGROUND: After pancreas transplantation, endocrine function is determined by the insulin secretory capacity of the transplanted pancreas. The authors evaluated the predictive value of postoperative oral glucose tolerance test (OGTT) and stimulated insulin secretion on long-term endocrine function. METHODS: Forty-one patients after pancreas-kidney transplantation with systemic venous drainage were studied. Patients were categorized to have normal glucose tolerance (NGT) or impaired glucose tolerance (IGT) (World Health Organization criteria: NGT, <7.8 mM; IGT, 7.8-11.1 mM 120 min after glucose intake) and high or low total insulin secretion. Mean follow-up of graft function and patient outcome was 10.2+/-0.5 years after OGTT. RESULTS: Patients with IGT had grafts with a longer ischemia time and a significantly worse urine amylase excretion as compared with patients with NGT. Using Kaplan-Meier survival analysis, patients with NGT had better long-term pancreatic function as compared with IGT in the follow-up after performing the first OGTT (mean, 10.9+/-0.2 vs. 8.8+/-0.9 years of graft function; P=0.02), but there was no difference in patient survival and kidney graft function. Also, high insulin secretion predicted significantly longer pancreas graft function as compared with low insulin secretion (P=0.04). CONCLUSIONS: Although IGT does not lead to poorer long-term patient survival and kidney graft function, it does predict compromised long-term endocrine function of the transplanted pancreas. Therefore, postoperative OGTT are useful tools for identification of patients at risk of long-term endocrine graft failure after pancreas transplantation.     

Evidence for early defects in insulin sensitivity and secretion before the onset of glucose dysregulation in obese youths: a longitudinal study

We sought to determine whether obese adolescents with high-"normal" 2-h post-oral glucose tolerance test glucose levels display defects in insulin secretion and sensitivity associated with future development of impaired glucose tolerance (IGT). Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp and insulin secretion by applying mathematical modeling during the hyperglycemic clamp in 60 normal glucose tolerance (NGT) obese adolescents, divided into three groups based on the 2-h glucose values (<100, 100-119, 120-139 mg/dL), and in 21 IGT obese adolescents. Glucose tolerance was reevaluated after 2 years. Insulin sensitivity decreased significantly across 2-h glucose NGT categories, while the highest NGT category and IGT group were similar. First-phase insulin secretion decreased across NGT categories, while no difference was found between the highest NGT group and IGT subjects. Second-phase secretion was similar across all NGT and IGT groups. The disposition index ((C)DI) decreased across NGT categories, while no difference was observed between the highest NGT and IGT subjects. Age and (C)DI were the best predictors of 2-h glucose after two years. Across rising categories of normal 2-h glucose levels, NGT obese adolescents exhibit significant impairment of β-cell function relative to insulin sensitivity associated with the development of IGT.     

Beta-cell function is a major contributor to oral glucose tolerance in high-risk relatives of four ethnic groups in the U.S

First-degree relatives of individuals with type 2 diabetes are at increased risk of developing hyperglycemia. To examine the prevalence and pathogenesis of abnormal glucose homeostasis in these subjects, 531 first-degree relatives with no known history of diabetes (aged 44.1 +/- 0.7 years; BMI 29.0 +/- 0.3 kg/m(2)) underwent an oral glucose tolerance test (OGTT). Newly identified diabetes was found in 19% (n = 100), and impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) was found in 36% (n = 191). Thus, only 45% (n = 240) had normal glucose tolerance (NGT). The homeostasis model assessment of insulin resistance (HOMA-IR) was used to estimate insulin sensitivity; beta-cell function was quantified as the ratio of the incremental insulin to glucose responses over the first 30 min during the OGTT (DeltaI(30)/DeltaG(30)). This latter measure was also adjusted for insulin sensitivity as it modulates beta-cell function ([DeltaI(30)/DeltaG(30)]/HOMA-IR). Decreasing glucose tolerance was associated with increasing insulin resistance (HOMA: NGT 12.01 +/- 0.54 pmol/mmol; IFG/IGT 16.14 +/- 0.84; diabetes 26.99 +/- 2.62; P < 0.001) and decreasing beta-cell function (DeltaI(30)/DeltaG(30): NGT 157.7 +/- 9.7 pmol/mmol; IFG/IGT 100.4 +/- 5.4; diabetes 57.5 +/- 7.3; P < 0.001). Decreasing beta-cell function was also identified when adjusting this measure for insulin sensitivity ([DeltaI(30)/DeltaG(30)]/HOMA-IR). In all four ethnic groups (African-American, n = 55; Asian-American, n = 66; Caucasian, n = 217; Hispanic-American, n = 193), IFG/IGT and diabetic subjects exhibited progressively increasing insulin resistance and decreasing beta-cell function. The relationships of insulin sensitivity and beta-cell function to glucose disposal, as measured by the incremental glucose area under the curve (AUCg), were examined in the whole cohort. Insulin sensitivity and AUCg were linearly related so that insulin resistance was associated with poorer glucose disposal (r(2) = 0.084, P < 0.001). In contrast, there was a strong inverse curvilinear relationship between beta-cell function and AUCg such that poorer insulin release was associated with poorer glucose disposal (log[DeltaI(30)/DeltaG(30)]: r(2) = 0.29, P < 0.001; log[(DeltaI(30)/DeltaG(30))/HOMA-IR]: r(2) = 0.45, P < 0.001). Thus, abnormal glucose metabolism is common in first-degree relatives of subjects with type 2 diabetes. Both insulin resistance and impaired beta-cell function are associated with impaired glucose metabolism in all ethnic groups, with beta-cell function seeming to be more important in determining glucose disposal.