High-dose oral vitamin C partially replenishes vitamin C levels in patients with Type 2 diabetes and low vitamin C levels but does not improve endothelial dysfunction or insulin resistance

Endothelial dysfunction is a hallmark of Type 2 diabetes related to hyperglycemia and oxidative stress. Nitric oxide-dependent vasodilator actions of insulin may augment glucose disposal. Thus endothelial dysfunction may worsen insulin resistance. Intra-arterial administration of vitamin C improves endothelial dysfunction in diabetes. In the present study, we investigated effects of high-dose oral vitamin C to alter endothelial dysfunction and insulin resistance in Type 2 diabetes. Plasma vitamin C levels in 109 diabetic subjects were lower than healthy (36 +/- 2 microM) levels. Thirty-two diabetic subjects with low plasma vitamin C (<40 microM) were subsequently enrolled in a randomized, double-blind, placebo-controlled study of vitamin C (800 mg/day for 4 wk). Insulin sensitivity (determined by glucose clamp) and forearm blood flow in response to ACh, sodium nitroprusside (SNP), or insulin (determined by plethysmography) were assessed before and after 4 wk of treatment. In the placebo group (n = 17 subjects), plasma vitamin C (22 +/- 3 microM), fasting glucose (159 +/- 12 mg/dl), insulin (19 +/- 7 microU/ml), and SI(Clamp) [2.06 +/- 0.29 x 10(-4) dl x kg(-1) x min(-1)/(microU/ml)] did not change significantly after placebo treatment. In the vitamin C group (n = 15 subjects), basal plasma vitamin C (23 +/- 2 microM) increased to 48 +/- 6 microM (P < 0.01) after treatment, but this was significantly less than that expected for healthy subjects (>80 microM). No significant changes in fasting glucose (156 +/- 11 mg/dl), insulin (14 +/- 2 microU/ml), SI(Clamp) [2.71 +/- 0.46 x 10(-4) dl x kg(-1) x min(-1)/(microU/ml)], or forearm blood flow in response to ACh, SNP, or insulin were observed after vitamin C treatment. We conclude that high-dose oral vitamin C therapy, resulting in incomplete replenishment of vitamin C levels, is ineffective at improving endothelial dysfunction and insulin resistance in Type 2 diabetes.     

Comparison of short-term diet and exercise on insulin action in individuals with abnormal glucose tolerance.

The effects of a 10-day low-calorie diet (LCD; n = 8) or exercise training (ET; n = 8) on insulin secretion and action were compared in obese men (n = 9) and women (n = 7), aged 53 +/- 1 yr, with abnormal glucose tolerance by using a hyperglycemic clamp with superimposed arginine infusion and a high-fat drink. Body mass (LCD, 115 +/- 5 vs. 110 +/- 5 kg; ET, 111 +/- 7 vs. 109 +/- 7 kg; P < 0. 01) and fasting plasma glucose (LCD, 115 +/- 10 vs. 99 +/- 4 mg/dl; ET, 112 +/- 4 vs. 101 +/- 5 mg/dl, P < 0.01) and insulin (LCD, 23.9 +/- 5.6 vs. 15.2 +/- 3.9 microU/ml; ET, 17.6 +/- 1.9 vs. 13.9 +/- 2. 4 microU/ml; P < 0.05) decreased in both groups. There was a 40% reduction in plasma insulin during hyperglycemia (0-45 min) after LCD (peak: 118 +/- 18 vs. 71 +/- 14 microU/ml; P < 0.05) and ET (69 +/- 14 vs. 41 +/- 7 microU/ml; P < 0.05) and trends for reductions during arginine infusion and a high-fat drink. The 56% increase in glucose uptake after ET (4.95 +/- 0.90 vs. 7.74 +/- 0.82 mg. min-1. kg fat-free mass-1; P < 0.01) was significantly (P < 0.01) greater than the 19% increase (5.72 +/- 1.12 vs. 6.80 +/- 0.94 mg. min-1. kg fat-free mass-1; P = not significant) that occurred after LCD. The marked increase in glucose disposal after ET, despite lower insulin levels, suggests that short-term exercise is more effective than diet in enhancing insulin action in individuals with abnormal glucose tolerance.     

Seven days of bed rest decrease insulin action on glucose uptake in leg and whole body

Impaired glucose tolerance develops in normal humans after short-term bed rest. To elucidate the mechanism, insulin action on whole body glucose uptake rate (WBGUR) and leg glucose uptake rate (LGUR) was measured by sequential euglycemic clamp technique combined with femoral arterial and venous cannulation at insulin concentrations of 10 +/- 1, 18 +/- 1, 37 +/- 2, and 360 +/- 15 microU/ml. Studies were performed before (C) and after (BR) 7 days of strict bed rest. WBGUR was significantly lower after bed rest than before (5.5 +/- 0.4 and 7.2 +/- 0.8 mg.min-1.kg-1, respectively) when insulin was 37 microU/ml. LGUR was even more markedly depressed by bed rest, being 0.6 +/- 0.1, 0.9 +/- 0.2, and 2.8 +/- 0.4 mg.min-1.kg leg-1 (BR) compared with 0.9 +/- 0.1, 1.7 +/- 0.4, and 5.9 +/- 0.5 mg.min-1.kg leg-1 (C) (P less than 0.05) at the three lower insulin concentrations. At these insulin concentrations also, lactate release and glucose oxidation and glycogen storage estimated by indirect calorimetry were lower in the leg after bed rest. At the highest insulin dose WBGUR was similar on BR and C days, while LGUR was lower after bed rest. In conclusion, 7 days of bed rest decrease whole body insulin action, a fact that is explained by decreased insulin action in inactive muscle.     

Insulin action and secretion in endurance-trained and untrained humans

To evaluate insulin sensitivity and responsiveness, a two-stage hyperinsulinemic euglycemic clamp procedure (insulin infusions of 40 and 400 mU.m-2.min-1) was performed on 11 endurance-trained and 11 untrained volunteers. A 3-h hyperglycemic clamp procedure (plasma glucose approximately 180 mg/dl) was used to study the insulin response to a fixed glycemic stimulus in 15 trained and 12 untrained subjects. During the 40-mU.m-2.min-1 insulin infusion, the glucose disposal rate was 10.2 +/- 0.5 mg.kg fat-free mass (FFM)-1.min-1 in the trained group compared with 8.0 +/- 0.6 mg.kg FFM-1.min-1 in the untrained group (P less than 0.01). In contrast, there was no significant difference in maximally stimulated glucose disposal: 17.7 +/- 0.6 in the trained vs. 16.7 +/- 0.7 mg.kg FFM-1.min-1 in the untrained group. During the hyperglycemic clamp procedure, the incremental area for plasma insulin was lower in the trained subjects for both early (0-10 min: 140 +/- 18 vs. 223 +/- 23 microU.ml-1.min; P less than 0.005) and late (10-180 min: 4,582 +/- 689 vs. 8,895 +/- 1,316 microU.ml-1.min; P less than 0.005) insulin secretory phases. These data demonstrate that 1) the improved insulin action in healthy trained subjects is due to increased sensitivity to insulin, with no change in responsiveness to insulin, and 2) trained subjects have a smaller plasma insulin response to an identical glucose stimulus than untrained individuals.     

Glucagon chronically impairs hepatic and muscle glucose disposal

Defects in insulin secretion and/or action contribute to the hyperglycemia of stressed and diabetic patients, and we hypothesize that failure to suppress glucagon also plays a role. We examined the chronic impact of glucagon on glucose uptake in chronically catheterized conscious depancreatized dogs placed on 5 days of nutritional support (NS). For 3 days of NS, a variable intraportal infusion of insulin was given to maintain isoglycemia (approximately 120 mg/dl). On day 3 of NS, animals received a constant low infusion of insulin (0.4 mU.kg-1.min-1) and either no glucagon (CONT), basal glucagon (0.7 ng.kg-1.min-1; BasG), or elevated glucagon (2.4 ng.kg-1.min-1; HiG) for the remaining 2 days. Glucose in NS was varied to maintain isoglycemia. An additional group (HiG+I) received elevated insulin (1 mU.kg-1.min-1) to maintain glucose requirements in the presence of elevated glucagon. On day 5 of NS, hepatic substrate balance was assessed. Insulin and glucagon levels were 10+/-2, 9+/-1, 7+/-1, and 24+/-4 microU/ml, and 24+/-5, 39+/-3, 80+/-11, and 79+/-5 pg/ml, CONT, BasG, HiG, and HiG+I, respectively. Glucagon infusion decreased the glucose requirements (9.3+/-0.1, 4.6+/-1.2, 0.9+/-0.4, and 11.3+/-1.0 mg.kg-1.min-1). Glucose uptake by both hepatic (5.1+/-0.4, 1.7+/-0.9, -1.0+/-0.4, and 1.2+/-0.4 mg.kg-1.min-1) and nonhepatic (4.2+/-0.3, 2.9+/-0.7, 1.9+/-0.3, and 10.2+/-1.0 mg.kg-1.min-1) tissues decreased. Additional insulin augmented nonhepatic glucose uptake and only partially improved hepatic glucose uptake. Thus, glucagon impaired glucose uptake by hepatic and nonhepatic tissues. Compensatory hyperinsulinemia restored nonhepatic glucose uptake and partially corrected hepatic metabolism. Thus, persistent inappropriate secretion of glucagon likely contributes to the insulin resistance and glucose intolerance observed in obese and diabetic individuals.     

Tetrahydrobiopterin increases insulin sensitivity in patients with type 2 diabetes and coronary heart disease

Tetrahydrobiopterin (BH(4)) is an essential cofactor of nitric oxide synthase that improves endothelial function in diabetics, smokers, and patients with hypercholesterolemia. Insulin resistance has been suggested as a contributing factor in the development of endothelial dysfunction via an abnormal pteridine metabolism. We hypothesized that BH(4) would restore flow-mediated vasodilation (FMD, endothelial-dependent vasodilation), which may affect insulin resistance in type 2 diabetic patients. Thirty-two subjects (12 type 2 diabetic subjects, 10 matched nondiabetic subjects, and 10 healthy unmatched subjects) underwent infusion of BH(4) or saline in a random crossover study. Insulin sensitivity index (S(I)) was measured by hyperinsulinemic isoglycemic clamp. FMD was measured using ultrasonography. BH(4) significantly increased S(I) in the type 2 diabetics [3.6 +/- 0.6 vs. 4.9 +/- 0.7 x 10(-4) dl.kg(-1).min(-1)/(microU/ml), P < 0.05], while having no effects in nondiabetics [8.9 +/- 1.1 vs. 9.0 +/- 0.9 x 10(-4) dl.kg(-1).min(-1)/(microU/ml), P = 0.92] or in healthy subjects [17.5 +/- 1.6 vs. 18 +/- 1.8 x 10(-4) dl.kg(-1).min(-1)/(microU/ml), P = 0.87]. BH(4) did not affect the relative changes in brachial artery diameter from baseline FMD (%) in type 2 diabetic subjects (2.3 +/- 0.8 vs. 1.8 +/- 1.0%, P = 0.42), nondiabetic subjects (5.3 +/- 1.1 vs. 6.6 +/- 0.9%, P = 0.32), or healthy subjects (11.9 +/- 0.6 vs. 11.0 +/- 1.0%, P = 0.48). In conclusion, BH(4) significantly increases insulin sensitivity in type 2 diabetic patients without any discernible improvement in endothelial function.     

Important role of glucagon during exercise in diabetic dogs

To define the role of immunoreactive glucagon (IRG) during exercise in diabetes, 12 insulin-deprived alloxan-diabetic (A-D) dogs were run for 90 min (100 m/min, 12 degrees) with or without somatostatin (St 0.5 microgram . kg-1 . min-1). Compared with normal dogs, A-D dogs were characterized by similar hepatic glucose production (Ra), lower glucose metabolic clearance, and higher plasma glucose and free fatty acid levels during rest and exercise. In A-D dogs IRG was greater at rest and exhibited a threefold greater exercise increment than controls, whereas immunoreactive insulin (IRI) was reduced by 68% at rest but had similar values to controls during exercise. Basal norepinephrine, epinephrine, cortisol, and lactate levels were similar in normal and A-D dogs. However, exercise increments in norepinephrine, cortisol, and lactate were higher in A-D dogs. When St was infused during exercise in the A-D dogs, IRG was suppressed by 432 +/- 146 pg/ml below basal and far below the exercise response in A-D controls (delta = 645 +/- 153 pg/ml). IRI was reduced by 1.8 +/- 0.2 microU/ml with St. With IRG suppression the increase in Ra seen in exercising A-D controls (delta = 4.8 +/- 1.6 mg . kg-1 . min-1) was virtually abolished, and glycemia fell by 104 to 133 +/- 37 mg/dl. Owing to this decrease in glycemia, the increase in glucose disappearance was attenuated. Despite the large fall in glucose during IRG suppression, counterregulatory increases were not excessive compared with A-D controls. In fact, as glucose levels approached euglycemia, the increments in norepinephrine and cortisol were reduced to levels similar to those seen in normal exercising dogs. In conclusion, IRG suppression during exercise in A-D dogs almost completely obviated the increase in Ra, resulting in a large decrease in plasma glucose. Despite this large fall in glucose, there was no excess counterregulation, since glucose concentrations never reached the hypoglycemic range.     

Muscle glucose transport: interactions of in vitro contractions, insulin, and exercise

Exercise increases permeability of muscle to glucose. Normally, the effects of exercise and a maximal insulin stimulus on glucose transport are additive. However, the combined effect on rat epitrochlearis muscle permeability to 3-O-methylglucose (3-MG) of a maximal insulin stimulus followed by in vitro contractile activity of 1.24 +/- 0.06 mumol.10 min-1.ml intracellular water-1 was no greater than that of either stimulus alone. We found that this absence of an additive effect was caused by prolonged exposure to an unphysiologically high insulin concentration (20,000 microU/ml for 60 min), which, in addition to stimulating glucose transport, appears to prevent further increases in permeability to glucose. When the treatments were reversed and muscles were first stimulated to contract and then incubated with 20,000 microU/ml insulin, 3-MG uptake (mumol.10 min-1.ml intracellular water-1) increased from a control value of 0.26 +/- 0.03 to 1.80 +/- 0.15, compared with 1.04 +/- 0.06 for contractile activity alone, 1.21 +/- 0.08 for insulin, and 1.88 +/- 0.11 for exercise (swimming) plus insulin. Swimming plus in vitro contractile activity did not have a greater effect than contractile activity alone. Our results provide evidence that 1) the effect of exercise on muscle permeability to glucose is mediated solely by a process associated with contractile activity, and 2) it is advisable to avoid the use of unphysiologically high insulin concentrations in studies designed to elucidate in vivo actions of insulin.     

Effect of hematocrit reduction on hormonal and metabolic responses to exercise

We wished to determine the effect of a 25% hematocrit reduction on glucoregulatory hormone release and glucose fluxes during exercise. In five anemic dogs, plasma glucose fell by 21 mg/dl and in five controls by 7 mg/dl by the end of the 90-min exercise period. After 50 min of exercise, hepatic glucose production (Ra) and glucose metabolic clearance rate (MCR) began to rise disproportionately in anemics compared with controls. By the end of exercise, the increase in Ra was almost threefold higher (delta 15.1 +/- 3.4 vs. delta 5.2 +/- 1.3 mg X kg-1 X min-1) and MCR nearly fourfold (delta 24.6 +/- 8.8 vs. delta 6.5 +/- 1.3 ml X kg-1 X min-1). Exercise with anemia, in relation to controls resulted in elevated levels of glucagon [immunoreactive glucagon (IRG) delta 1,283 +/- 507 vs delta 514 +/- 99 pg/ml], norepinephrine (delta 1,592 +/- 280 vs. delta 590 +/- 155 pg/ml), epinephrine (delta 2,293 +/- 994 vs. delta 385 +/- 186 pg/ml), cortisol (delta 6.7 +/- 2.2 vs. delta 2.1 +/- 1.0 micrograms/dl) and lactate (delta 12.1 +/- 2.2 vs. delta 4.2 +/- 1.8 mg/dl) after 90 min. Immunoreactive insulin and free fatty acids were similar in both groups. In conclusion, exercise with a 25% hematocrit reduction results in 1) elevated lactate, norepinephrine, epinephrine, cortisol, and IRG levels, 2) an increased Ra which is likely related to the increased counterregulatory response, and 3) we speculate that a near fourfold increase in MCR is related to metabolic changes due to hypoxia in working muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of insulin on glucose uptake in near-term fetal lambs

Glucose clamp experiments were performed in 27 chronically catheterized, late-gestation fetal lambs in order to measure the effect of fetal insulin concentration on fetal glucose uptake at a constant glucose concentration. Fetal arterial blood glucose concentration was measured over a 30-min control period and then maintained at the control value by a variable glucose infusion into the fetus while insulin was infused at a constant rate into the fetus. Plasma insulin concentration increased from 21 +/- 10 (SD) to 294 +/- 179 (SD) microU X ml-1. The exogenous glucose infusion rate necessary to maintain constant glycemia during the plateau hyperinsulinemia averaged 4.3 +/- 1.6 (SD) mg X min-1 X kg-1. In a subset of 13 animals, total fetal exogenous glucose uptake (FGU; sum of glucose uptake from the placenta via the umbilical circulation plus the steady-state exogenous glucose infusion rate) was measured during the control and hyperinsulinemia period. FGU was directly related to insulin concentration (y = 4.24 + 0.07x) at insulin levels less than 100 microU/ml and increased 132% above control at insulin levels above 100 microU/ml. Hyperinsulinemia did not affect fetal glucose uptake from the placenta via the umbilical circulation. These studies demonstrate that insulin concentration is a major factor controlling glucose uptake in the near-term fetal lamb, and that an increase of fetal insulin does not affect the transport of glucose to the fetus from the placenta.     

Growth hormone and carbohydrate intolerance in cirrhosis

Patients with cirrhosis of the liver often have insulin resistance and elevated circulating growth hormone levels. This study was undertaken (a) to evaluate glucose intolerance, insulin resistance and abnormal growth hormone secretion and (b) to determine if GH suppression improves insulin resistance. Glucose tolerance tests (GTT), intravenous insulin tolerance tests (IVITT), arginine stimulation tests (AST) and glucose clamp studies before and during GH suppression with somatostatin were performed in a group of patients with alcohol-induced liver cirrhosis. During GTT cirrhotic subjects had a 2-hour plasma glucose of 200 +/- 9.8 ng/dl (N = 14) compared to 128 +/- 8.0 ng/dl in normal controls (N = 15), P less than 0.001. Basal GH was elevated in cirrhotic patients and in response to arginine stimulation reached a peak of 17.0 +/- 5.4 ng/ml (N = 7), compared to a peak of 11.3 +/- 1.8 ng/ml in 5 normal controls (P = NS). During IVITT patients with cirrhosis had a glucose nadir of 60.0 +/- 4.0 mg/dl (N = 9), compared to 29.0 +/- 7.0 mg/dl in controls (N = 5), P less than 0.001. Peak GH levels during IVITT were not significantly different in cirrhotics and controls. Glucose utilization rates in 4 patients with cirrhosis of the liver before somatostatin mediated GH suppression was 3.1 +/- 0.5 mg/kg/min and 6.5 +/- 1.5 mg/kg/min during somatostatin infusion, P less than 0.025. We conclude that patients with alcohol induced cirrhosis have sustained GH elevations resulting in insulin resistance which improves after GH suppression.     

Failure of hyperketonemia to alter basal and insulin-mediated glucose metabolism in man

The effect of physiologic elevations of plasma hydroxybutyrate induced by the infusion of sodium D,L-beta-hydroxybutyrate (15 mumol X kg-1 X min-1) on carbohydrate metabolism was examined with the euglycemic insulin clamp technique in nine healthy volunteers. Plasma insulin concentration was acutely raised and maintained at 126 +/- 6 microU/ml and plasma glucose was held constant at the fasting level by a variable glucose infusion. Glucose uptake of 6.53 +/- 0.80 mg X kg-1 X min-1 was unchanged by hyperketonemia when compared with an intraindividual control study using saline instead of beta-OH-butyrate infusion (6.26 +/- 0.59 mg X kg-1 X min-1). In studies, in which the degree of metabolic alkalosis accompanying butyrate infusion was mimicked by the continuous administration of bicarbonate, glucose uptake was also unaffected (6.25 +/- 0.45 mg X kg-1 X min-1). Furthermore, hyperketonemia had no effect on basal glucose production or the suppression of hepatic glucose production following hyperinsulinemia. It is concluded that moderate elevations in plasma beta-hydroxy-butyrate do not alter hepatic or peripheral glucose metabolism.     

Alterations in liver, muscle, and adipose tissue insulin sensitivity in men with HIV infection and dyslipidemia

Dyslipidemia is common in patients with HIV infection. In this study, a two-stage euglycemic hyperinsulinemic clamp, with infusion of stable isotopically labeled tracers, was used to evaluate insulin action in skeletal muscle, liver, and adipose tissue in HIV-infected men with dyslipidemia (HIV-DL; plasma triglyceride >250 mg/dl and HDL <45 mg/dl; n=12), HIV-infected men without dyslipidemia (HIV w/o DL; n=12), and healthy men (n=6). Basal rates of glucose production (glucose R(a)), glucose disposal (glucose R(d)), and lipolysis (palmitate R(a)) were similar between groups. The relative suppression of glucose R(a) (63+/- 4, 77+/- 2, and 78+/- 3%, P=0.008) and palmitate R(a) (49+/-4, 63+/-3, and 68+/-3%, P=0.005) during ow-dose insulin infusion (plasma insulin approximately 30 microU/ml), and the relative stimulation of glucose R(d) (214+/-21, 390+/-25, and 393+/-46%, P=0.001) during high-dose insulin infusion (plasma insulin approximately 75 microU/ml) were lower in HIV-DL than in HIV w/o DL and healthy volunteers, respectively. Suppression of basal glucose R(a) correlated with plasma adiponectin (r=0.44, P=0.02) and inversely with plasma IL-6 (r=-0.49, P<0.001). Stimulation of glucose R(d) correlated directly with adiponectin (r=0.48, P<0.01) and inversely with IL-6 (r=-0.49, P=0.02). We conclude that dyslipidemia in HIV-infected men is indicative of multiorgan insulin resistance, and circulating adipokines may be important in the pathogenesis of impaired insulin action.     

Myocardial function and energy substrate metabolism in the insulin-resistant JCR:LA corpulent rat.

Alterations in myocardial energy substrate utilization contribute to the development of cardiomyopathic changes in insulin-dependent and non-insulin-dependent diabetic rats. Energy substrate utilization and contractile function, however, have not been characterized in insulin-resistant diabetes. In this study, we studied these parameters in the insulin-resistant obese JCR:LA-cp rat homozygous for the corpulent gene (cp/cp). Homozygous (+/+) or heterozygous (+/cp) lean non-insulin-resistant rats were used as controls. Isolated working hearts from cp/cp and lean control rats were perfused with Krebs-Henseleit buffer containing either 11 mM [U-14C]glucose and 0.4 mM palmitate or 11 mM glucose and 0.4 mM [1-14C]palmitate. Unlike control hearts, hearts from cp/cp rats were found to require high doses of insulin and Ca2+ concentrations of less than or equal to 1.75 mM to maintain mechanical function. In the presence of 2,000 microU/ml insulin, contractile function from cp/cp rat hearts was not depressed in the presence of either 1.25 or 1.75 mM Ca2+. Steady-state glucose oxidation rates in hearts perfused with 1.25 mM Ca2+ and 2,000 microU/ml insulin were 811 +/- 86 (SE) and 612 +/- 51 nmol.min-1.g dry wt-1 in cp/cp and control rats, respectively. Palmitate oxidation was 307 +/- 47 and 307 +/- 47 nmol.min-1.g dry wt-1 in cp/cp and lean control hearts, respectively. Under these perfusion conditions, 40% of myocardial ATP production was derived from glucose, whereas 60% was derived from palmitate in both cp/cp and control rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of infection on glucose-dependent liver glucose uptake during TPN: interaction with insulin

Chronic total parenteral nutrition (TPN) markedly augments net hepatic glucose uptake (NHGU). This adaptive increase is impaired by an infection despite accompanying hyperinsulinemia. In the nonadapted state, NHGU is dependent on the prevailing glucose levels. Our aims were to determine whether the adaptation to TPN alters the glucose dependence of NHGU, whether infection impairs this dependence, and whether insulin modulates the glucose dependence of NHGU during infection. Chronically catheterized dogs received TPN for 5 days. On day 3 of TPN, dogs received either a bacterial fibrin clot to induce a nonlethal infection (INF, n = 9) or a sterile fibrin clot (Sham, n = 6). Forty-two hours after clot implantation, somatostatin was infused. In Sham, insulin and glucagon were infused to match the level seen in Sham (9 +/- 1 microU/ml and 23 +/- 4 pg/ml, respectively). In infected animals, either insulin and glucagon were infused to match the levels seen in infection (25 +/- 2 microU/ml and 101 +/- 15 pg/ml; INF-HI; n = 5) or insulin was replaced to match the lower levels seen in Sham (13 +/- 2 microU/ml), whereas glucagon was kept elevated (97 +/- 9 pg/ml; INF-LO; n = 4). Then a four-step (90 min each) hyperglycemic (120, 150, 200, or 250 mg/dl) clamp was performed. NHGU increased at each glucose step in Sham (from 3.6 +/- 0.6 to 5.4 +/- 0.7 to 8.9 +/- 0.9 to 12.1 +/- 1.1 mg.kg(-1).min(-1)); the slope of the relationship between glucose levels and NHGU (i.e., glucose dependence) was higher than that seen in nonadapted animals. Infection impaired glucose-dependent NHGU in both INF-HI (1.3 +/- 0.4 to 2.9 +/- 0.5 to 5.5 +/- 1.0 to 7.7 +/- 1.6 mg.kg(-1).min(-1)) and INF-LO (0.5 +/- 0.7 to 2.2 +/- 0.6 to 4.2 +/- 1.0 to 5.8 +/- 0.8 mg.kg(-1).min(-1)). In summary, TPN augments glucose-dependent NHGU, the presence of infection decreases glucose-dependent NHGU, and the accompanying hyperinsulinemia associated with infection does not sustain the glucose dependence of NHGU.     

Enteral infusion of glucose at rates approximating EGP enhances glucose disposal but does not cause hypoglycemia

Portal infusion of glucose at rates approximating endogenous glucose production (EGP) causes paradoxical hypoglycemia in wild-type but not GLUT2 null mice, implying activation of a specific portal glucose sensor. To determine whether this occurs in humans, glucose containing [3-3H]glucose was infused intraduodenally at rates of 3.1 mg. kg-1. min-1 (n = 5), 1.55 mg. kg-1. min-1 (n = 9), or 0/0.1 mg. kg-1. min-1 (n = 9) for 7 h in healthy nondiabetic subjects. [6,6-2H2]glucose was infused intravenously to enable simultaneous measurement of EGP, glucose disappearance, and the rate of appearance of the intraduodenally infused glucose. Plasma glucose concentrations fell (P < 0.01) from 90 +/- 1 to 84 +/- 2 mg/dl during the 0/0.1 mg. kg-1. min-1 id infusions but increased (P < 0.001) to 104 +/- 5 and 107 +/- 3 mg/dl, respectively, during the 1.55 and 3.1 mg. kg-1. min-1 id infusions. In contrast, insulin increased (P < 0.05) during the 1.55 and 3.0 mg. kg-1. min-1 infusions, reaching a peak of 10 +/- 2 and 18 +/- 5 micro U/ml, respectively, by 2 h. Insulin concentrations then fell back to concentrations that no longer differed by study end (7 +/- 1 vs. 8 +/- 1 micro U/ml). This resulted in comparable suppression of EGP by study end (0.84 +/- 0.2 and 0.63 +/- 0.1 mg. kg-1. min-1). Glucose disappearance was higher (P < 0.01) during the final hour of the 3.1 than 1.55 mg. kg-1. min-1 id infusion (4.47 +/- 0.2 vs. 2.6 +/- 0.1 mg. kg-1. min-1), likely because of the slightly, but not significantly, higher glucose and insulin concentrations. We conclude that, in contrast to mice, selective portal glucose delivery at rates approximating EGP does not cause hypoglycemia in humans.     

Effect of sparteine sulfate on insulin secretion in normal men

This study aimed at evaluating the influence of sparteine sulfate either upon basal plasma glucose and insulin or glucose-induced insulin secretion in normal man. Thirteen overnight fasted volunteers took part in this study; five of them were submitted to sparteine sulfate bolus (15 mg in 10 ml of saline solution) followed by a slow infusion (90 mg/100 ml X 60 min) and eight subjects underwent two different glucose pulses (20 gr. i.v.) in absence or in presence of sparteine, infused as described above. In basal conditions, along with sparteine infusion, plasma glucose showed a progressive and significant decrease (P less than 0.0001) and plasma insulin was significantly higher from min 10 to 120' (P less than 0.0005-0.001). Even during the glucose-induced insulin secretion, in the presence of sparteine infusion, plasma glucose levels were significantly lower while plasma insulin levels were significantly higher when compared to those observed after glucose alone. The acute insulin response (AIR) was 42 +/- 10 microU/ml after glucose alone vs 67 +/- 9 microU/ml after glucose plus sparteine (P less than 0.05). Total insulinemic areas were significantly different being 1410 +/- 190 vs 2250 +/- 310 microU/ml/min (P less than 0.001) during glucose and glucose plus sparteine infusion, respectively. This study thereby, demonstrates that in normal man sparteine sulfate, administrated by intravenous infusion, is able to increase either basal or glucose-induced insulin secretion.     

Glucose tolerance and insulinemia in patients with hepatic cirrhosis and portal hypertension treated by portacaval anastomosis]

Development of diabetes mellitus is a common complication of side to side porta-caval anastomosis (PCA). Five patients with liver cirrhosis and portal hypertension have been studied with intravehous (IVGTT, 0,5 g/Kg B.W.) and oral (OGTT, 1 g/Kg B.W.) glucose tolerance tests before and three weeks after PCA. Fasting plasma glucose was 84 +/- 7 before and 87 +/- 3 mg/dl after PCA. Fasting IRI increased from 17 +/- 3 to 31 +/- 6 microU/ml. The pattern of plasma glucose and IRI response to IVGTT did not change after PCA. Plasma glucose resonse to OGTT after PCA showed only an earlier rise at 60 instead of 90 minutes, whereas IRI resonse (area under the insulin curve) was significantly enhanced (from 12.4 to 19.8 U/l, p < 0.05). These data suggest a role of gut polipeptides in determining hyperinsulinemia and insulin resistence in PCA patients.     

Type 2 diabetes mellitus in a non-obese mouse model induced by Meg1/Grb10 overexpression

We assessed the possibility of C57BL/6-Tg (Meg1/Grb10)isn(Meg1 Tg) mice as a non-obese type 2 diabetes (2DM) animal model. Meg1 Tg mice were born normal, but their weight did not increase as much as normal after weaning and showed about 85% of normal size at 20 weeks of age. Body mass index of Meg1 Tg mice was also smaller than that of control mice. The glucose tolerance test and insulin tolerance test showed that Meg1 Tg mice had reduced ability to normalize the blood glucose level. Blood urea nitrogen (BUN) in Meg1 Tg mice (19.6 +/- 1.2 mg/dl) was significantly lower than in controls (22.0 +/- 0.8 mg/dl), while plasma triglyceride, insulin, adiponectin, and resistin levels were significantly higher (202.0 +/- 23.4 mg/dl vs 146.3 +/- 23.4 mg/dl, 152.4 +/- 16.3 pg/ml vs 88.1 +/- 16.9 pg/ml, 74.4 +/- 10.9 microg/ml vs 48.3 +/- 7.0 microg/ml, and 4.0 +/- 0.2 ng/ml vs 3.6 +/- 0.2 ng/ml, respectively). Body, visceral fat weight and liver weights were significantly lower (19.6 +/- 0.4 g vs 24.3 +/- 0.3 g, 376.7 +/- 29.6 mg to 507.5 +/- 23.0 mg, and 906.0 +/- 41.8 mg to 1,001.0 +/- 15.1 mg, respectively). Thus, hyperinsulinemia observed in Meg1 Tg mice indicates that their insulin signaling pathway is somehow inhibited. With high fat diet, the diabetes onset rate of Meg1 Tg mice increased up to 60%. These results suggest that Meg1 Tg mice resemble human 2DM.     

Glucose uptake by adipocytes of obese rats: effect of one bout of acute exercise.

The effect of one bout of acute exercise on impaired glucose metabolism was studied in obese (480 +/- 20 g), untrained rats, at rest (n = 10) and after 60 min of swimming (n = 5). Using the euglycemic, hyperinsulinemic (10 mU.kg-1 x min-1) clamp, glucose clearance rate increased from 7.6 +/- 0.9 at rest to 9.7 +/- 0.5 mL.kg-1 x min-1 after exercise (p < 0.05). Glucose (3-O-[14C]methylglucose) transport (GT) into epididymal adipocytes were incubated with or without insulin. In the absence of insulin, GT was 0.13 +/- 0.02 and 0.26 +/- 0.07 fmol.cell-1 x min-1 at rest and after exercise, respectively. In the presence of insulin (25-1000 microU.mL-1) GT increased at rest from 0.97 +/- 0.08 to 1.13 +/- 0.07 fmol.cell-1 x min-1, and after exercise from 1.35 +/- 0.05 to 1.87 +/- 0.11 fmol.cell-1 x min-1. GT was significantly higher after exercise compared with rest (p < 0.004). At rest, maximal insulin effect was achieved at 100 microU.mL-1, whereas with exercise, GT increased gradually with the insulin dosage. The following may be concluded: (i) the biological effect of insulin is amplified in obese rats by one bout of exercise and (ii) exercise affects GT into enlarged adipocytes by enhancing tissue responsiveness to insulin and by a cellular mechanism unrelated to the insulin action.