Exogenous Glucose Infusion Research Articles

Evaluation of insulin secretion and action in New World camelids

To measure and compare insulin secretion and sensitivity in healthy alpacas and llamas via glucose clamping techniques. 8 llamas and 8 alpacas. Hyperinsulinemic euglycemic clamping (HEC) and hyperglycemic clamping (HGC) were performed on each camelid in a crossover design with a minimum 48-hour washout period between clamping procedures. The HEC technique was performed to measure insulin sensitivity. Insulin was infused IV at 6 mU/min/kg for 4 hours, and an IV infusion of glucose was adjusted to maintain blood glucose concentration at 150 mg/dL. Concentrations of blood glucose and plasma insulin were determined throughout. The HGC technique was performed to assess insulin secretion in response to exogenous glucose infusion. An IV infusion of glucose was administered to maintain blood glucose concentration at 320 mg/dL for 3 hours, and concentrations of blood glucose and plasma insulin were determined throughout. Alpacas and llamas were not significantly different with respect to whole-body insulin sensitivity during HEC or in pancreatic β-cell response during HGC. Alpacas and llamas had markedly lower insulin sensitivity during HEC and markedly lower pancreatic β-cell response during HGC, in comparison with many other species. New World camelids had lower glucose-induced insulin secretion and marked insulin resistance in comparison with other species. This likely contributes to the disorders of fat and glucose metabolism that are common to camelids.

Activation of N-Methyl-d-aspartate (NMDA) Receptors in the Dorsal Vagal Complex Lowers Glucose Production

Diabetes is characterized by hyperglycemia due partly to increased hepatic glucose production. The hypothalamus regulates hepatic glucose production in rodents. However, it is currently unknown whether other regions of the brain are sufficient in glucose production regulation. The N-methyl-D-aspartate (NMDA) receptor is composed of NR1 and NR2 subunits, which are activated by co-agonist glycine and glutamate or aspartate, respectively. Here we report that direct administration of either co-agonist glycine or NMDA into the dorsal vagal complex (DVC), targeting the nucleus of the solitary tract, lowered glucose production in vivo. Direct infusion of the NMDA receptor blocker MK-801 into the DVC negated the metabolic effect of glycine. To evaluate whether NR1 subunit of the NMDA receptor mediates the effect of glycine, NR1 in the DVC was inhibited by DVC NR1 antagonist 7-chlorokynurenic acid or DVC shRNA-NR1. Pharmacological and molecular inhibition of DVC NR1 negated the metabolic effect of glycine. To evaluate whether the NMDA receptors mediate the effects of NR2 agonist NMDA, DVC NMDA receptors were inhibited by antagonist D-2-amino-5-phosphonovaleric acid (D-APV). DVC D-APV fully negated the ability of DVC NMDA to lower glucose production. Finally, hepatic vagotomy negated the DVC glycine ability to lower glucose production. These findings demonstrate that activation of NR1 and NR2 subunits of the NMDA receptors in the DVC is sufficient to trigger a brain-liver axis to lower glucose production, and suggest that DVC NMDA receptors serve as a therapeutic target for diabetes and obesity.

Skeletal Muscle Insulin Resistance Is the Primary Defect in Type 2 Diabetes

Insulin resistance is a characteristic feature of type 2 diabetes and plays a major role in the pathogenesis of the disease (1,2). Although β-cell failure is the sine qua non for development of type 2 diabetes, skeletal muscle insulin resistance is considered to be the initiating or primary defect that is evident decades before β-cell failure and overt hyperglycemia develops (3,4). Insulin resistance is defined as a reduced response of target tissues (compared with subjects with normal glucose tolerance [NGT] without a family history of diabetes), such as the skeletal muscle, liver, and adipocytes, to insulin. Because skeletal muscle is the predominant site of insulin-mediated glucose uptake in the postprandial state, here we will focus on recent advances about the time of onset, as well as the mechanism, of the skeletal muscle insulin resistance. The euglycemic insulin clamp technique (5) is considered to be the gold standard for measuring insulin action in vivo. With this technique, whole-body insulin action is quantified as the rate of exogenous glucose infusion (plus any residual hepatic glucose production) required to maintain the plasma glucose concentration at euglycemic levels in response to a fixed increment in the plasma insulin concentration. Because 80–90% of the infused glucose is taken up by skeletal muscle under conditions of euglycemic hyperinsulinemia, insulin sensitivity measured with the insulin clamp technique primarily reflects skeletal muscle (6). Another advantage of this technique is that it can be combined with indirect calorimetry to measure different substrate oxidation rates and with muscle biopsy to examine the biochemical/molecular etiology of the insulin resistance. Measurement of insulin sensitivity by the frequently sampled intravenous glucose tolerance test reflects both hepatic and peripheral insulin resistance and correlates well with the insulin clamp technique (7). Because insulin clamp studies are not feasible in large …

An islet population model of the endocrine pancreas

An islet population model is proposed for pancreatic insulin secretion. Without detailing the chain of biochemical events giving rise to the delivery of insulin packets, the effect of the islets' bursting response to varying glucose concentration is described by a simple second order nonlinear model, of the same functional form for all islets, but with a random distribution of parameter values over the one million islets considered. The islet equations are coupled to a traditional model of the glucose/insulin dynamics to complete a description of the feed-back control of the glucose/insulin system. The model is thus based upon the completely random cooperation of a large number of independent controllers, all reacting to the same prevailing plasma glucose concentrations, but with distributed reaction characteristics. It is shown that the proposed model is able to replicate in silico different observed phenomena such as low frequency glycemia-insulinemia oscillations (ultradian oscillations, with a period between 50 and 150 min, amplified by constant glucose administration and entrained by an oscillating exogenous glucose infusion), as well as concordant induction of high-frequency insulin oscillations by a rapid periodic pulsatile glucose infusion. In order to reproduce by simulation all of the above observed phenomena, a single set of (hyper-)parameters has been used throughout, showing that it is indeed possible that a single model may explain the results of several published experimental protocols.

Intestinal Cholecystokinin Controls Glucose Production through a Neuronal Network

Cholecystokinin (CCK) is a peptide hormone that is released from the gut in response to nutrients such as lipids to lower food intake. Here we report that a primary increase of CCK-8, the biologically active form of CCK, in the duodenum lowers glucose production independent of changes in circulating insulin levels. Furthermore, we show that duodenal CCK-8 requires the activation of the gut CCK-A receptor and a gut-brain-liver neuronal axis to lower glucose production. Finally, duodenal CCK-8 fails to lower glucose production in the early onset of high-fat diet-induced insulin resistance. These findings reveal a role for gut CCK that lowers glucose production through a neuronal network and suggest that intestinal CCK resistance may contribute to hyperglycemia in response to high-fat feeding.

Effect of Age of Infusion Site and Type of Rapid-Acting Analog on Pharmacodynamic Parameters of Insulin Boluses in Youth With Type 1 Diabetes Receiving Insulin Pump Therapy

OBJECTIVE—The purpose of this study was to examine the effect of type of insulin analog and age of insertion site on the pharmacodynamic characteristics of a standard insulin bolus in youth with type 1 diabetes receiving insulin pump therapy.RESEARCH DESIGN AND METHODS—Seventeen insulin pump–treated adolescents with type 1 diabetes underwent two euglycemic clamp procedures after a 0.2 unit/kg bolus of either insulin aspart or lispro on day 1 and day 4 of insulin pump site insertion. The glucose infusion rate (GIR) required to maintain euglycemia was the primary pharmacodynamic measure.RESULTS—There were no statistically significant differences in any of the pharmacodynamic parameters between aspart and lispro during day 1 and day 4. However, when the two groups were combined, time to discontinuation of exogenous glucose infusion, and time to half-maximal onset and offset of insulin action were observed significantly earlier during day 4 compared with day 1 (P = 0.03–0.0004), but the overall area under the GIR curve was similar on day 1 and day 4.CONCLUSIONS—With both insulin aspart and lispro, there is an earlier peak and shorter duration of action with increasing duration of infusion site use, but overall insulin action is not affected.

Insulin Resistance and Decreased Glucose-Stimulated Insulin Secretion After Acute Olanzapine Administration

The newer atypical antipsychotics, as a class, have been associated with an increased risk of weight gain and metabolic abnormalities. The mechanisms underlying this phenomenon are currently unclear, but there are data to suggest the possibility of an immediate (as opposed to chronic) effect of these drugs. The aim of the present study was to assess the acute effects of olanzapine on specific measures of insulin sensitivity and secretion. Healthy animals were tested in either the hyperinsulinemic-euglycemic or the hyperglycemic clamp. After reaching steady state in the hyperinsulinemic-euglycemic clamp, rats were injected with olanzapine (3 mg/kg sc) and monitored for an additional 130 minutes. In the hyperglycemic clamp, olanzapine was injected approximately 90 minutes before receiving a glucose bolus, and hyperglycemia was maintained via exogenous glucose infusion for an additional 90 minutes. Insulin and C-peptide levels were monitored throughout this clamp.Acute administration of olanzapine significantly lowered the glucose infusion rate due to an increase in hepatic glucose production and a decrease in glucose utilization. Olanzapine pretreatment induced hyperglycemia and markedly decreased plasma insulin and C-peptide in response to the glucose challenge. These findings indicate that olanzapine can directly induce metabolic changes that occur rapidly and well in advance of the changes that might be anticipated as a result of its weight-gain liability. We present novel findings highlighting an olanzapine-induced deficit in beta-cell functioning.

Comparison of effects of combined ACE inhibitor and low‐dose thiazide diuretic with ACE inhibitor alone on insulin action in patients with hypertension and Type 2 diabetes: a double‐blind crossover study

To establish the safety in terms of insulin sensitivity of a low dose thiazide/ACE inhibitor combination. We examined the effects on insulin sensitivity of captopril either alone or in combination with low-dose bendroflumethiazide (1.25 mg) in 15 hypertensive Type 2 diabetic patients. Insulin action was assessed using an isoglycaemic hyperinsulinaemic clamp in a double-blind, randomised, crossover study after a 6-week placebo run-in and following two 12-week treatment periods with captopril (C) (100 mg) alone or in combination with bendroflumethiazide (CB) (1.25 mg). Blood pressure was lower following CB compare to C (138/83 vs. 144/85 mmHg; P < 0.05) and both were lower than baseline (153/92 mmHg; P < 0.01). CB resulted in a significant increase in fasting plasma glucose compared to C (9.6 +/- 2.6 vs. 8.5 +/- 1.6 mmol/l; P < 0.05). Exogenous glucose infusion rates required to maintain isoglycaemia during hyperinsulinaemia were lower after CB compared to C (25.1 +/- 13.3 vs. 34.2 +/- 16.8 micromol/kg/min; P < 0.01) as were isotopically determined glucose utilisation rates (29.0 +/- 12.4 vs. 36.6 +/- 17.3 micromol/kg/min; P < 0.05). There was no significant difference in fasting endogenous glucose production between treatments (CB 9.3 +/- 3.3 vs. C 8.6 +/- 1.6 micromol/kg/min), nor between suppression following insulin (CB 4.0 +/- 2.1 vs. C 4.3 +/- 3.1 micromol/kg/min). Combination of low-dose bendroflumethiazide with captopril lowered blood pressure but resulted in deleterious effects on insulin action compared to captopril alone.

Effect of chronic growth hormone and hyperinsulinemic euglycemia on endogenous glucose production and utilization in periparturient dairy cows

Twenty-one periparturient Holstein cows were used to assess the effects of chronic intramuscular growth hormone (GH) and hyperinsulinemic euglycemia (HE) on glucose rate of appearance (Ra) into plasma. Cows were administered intramuscular GH (40 mg) or saline (CTL) daily for 96 h beginning either 25 d prepartum (GH, n=5; CTL, n=6) or 5 d postpartum (GH, n=6; CTL, n=4). Glucose Ra into plasma was determined using tracer methodologies on d 4 of treatment during basal condition and again during a period of HE. The period of HE was initiated immediately after the basal period and lasted for 4 h. It involved a 2 μg*kg−1 infusion of bovine insulin with maintenance of glycemia within 10% of the pre-insulin baseline by intrajugular infusion of exogenous glucose. The HE decreased endogenous glucose Ra to a greater extent postpartum than it did prepartum (P<0.001). Chronic GH increased endogenous glucose Ra (P=0.03); however there were no interactions of GH with physiological state (pre- vs. postpartum) or degree of suppression of endogenous Ra by HE. The amount of exogenous glucose needed to maintain euglycemia during HE was not affected by GH (P≥0.20). In conclusion, there were no interactions of chronic GH with insulin relative to glucose metabolism. However, insulin did have differential effects on glucose metabolism during the pre-and postpartum periods. Project funded by internal sources.

Intermittent hypoxia reverses the diurnal glucose rhythm and causes pancreatic β‐cell replication in mice

Obstructive sleep apnoea (OSA) and type 2 diabetes frequently co-exist and potentially interact haemodynamically and metabolically. However, the confounding effects of obesity have obscured the examination of any independent or interactive effects of the hypoxic stress of OSA and the hyperglycaemia of type 2 diabetes on haemodynamic and metabolic outcomes. We have developed a chronically catheterized, unhandled, lean murine model to examine the effects of intermittent hypoxic (IH) exposure and exogenous glucose infusion on the diurnal pattern of arterial blood pressure and blood glucose, as well as pancreatic beta-cell growth and function. Four experimental groups of adult male C57BL/J mice were exposed to 80 h of (1) either IH (nadir of inspired oxygen 5-6% at 60 cycles h(-1) for 12 h during light period) or intermittent air (IA; control) and (2) continuous infusion of either 50% dextrose or saline (control). IH exposure during saline infusion caused a sustained increase in arterial blood pressure of 10 mmHg (P < 0.0001), reversed the normal diurnal rhythm of blood glucose (P < 0.03), doubled corticosterone levels (P < 0.0001), and increased replication of pancreatic beta-cells from 1.5 +/- 0.3 to 4.0 +/- 0.8% bromodeoxyuridine (BrdU)-positive) beta-cells. The combined stimulus of IH exposure and glucose infusion attenuated the hypertension, exacerbated the reversed diurnal glucose rhythm, and produced the highest rates of apoptosis in beta-cells, without any additive effects on beta-cell replication. We conclude that, in contrast to the development of sustained hypertension, IH impaired glucose homeostasis only during periods of hypoxic exposure. IH acted as a stimulus to pancreatic beta-cell replication, but the presence of hyperglycaemia may increase the hypoxic susceptibility of beta-cells. This model will provide a basis for future mechanistic studies as well as assessing the metabolic impact of common comorbities in OSA, including obesity, insulin resistance and type 2 diabetes.

Stunning, Hibernation, and Assessment of Myocardial Viability

The last 3 decades have witnessed an unprecedented improvement in the outcome of patients with acute coronary syndromes. The widespread use of thrombolytic therapy and percutaneous coronary interventions, in association with increasingly potent antithrombotic agents, has contributed to significant reductions in mortality and morbidity in these patients. Although overall survival has improved, a downside of this success has been the greater number of patients with residual left ventricular (LV) dysfunction undergoing progressive LV remodeling and congestive heart failure. This problem is compounded by the rising age of our population and the higher prevalence of comorbidities such as diabetes mellitus that confer an increased risk of coronary artery disease (CAD) and congestive heart failure. Patients with CAD represent by far the most numerous cohort among those with congestive heart failure, and their treatment remains a partial success.1 Typically, these patients have multivessel disease, increased LV volumes, and variable degrees of regional and/or global systolic dysfunction, although more cases of isolated diastolic dysfunction have been reported recently.2–4 In these patients, coronary revascularization may lead to symptomatic and prognostic improvement, and these clinical benefits are accompanied by evidence of reverse LV remodeling. In this context, the concept of myocardial viability was developed and a number of different techniques have been used to demonstrate the presence of viable tissue before coronary revascularization. The aim of this review article is to summarize our current understanding of the concept of myocardial viability and its clinical implications in patients with CAD and chronic LV dysfunction. Throughout this review, we use the term viability to describe dysfunctional myocardium subtended by diseased coronary arteries with limited or absent scarring that therefore has the potential for functional recovery. Viability is a prospective definition, but it does not imply evidence of functional recovery after interventions. The term hibernation, which …

Effects of atazanavir/ritonavir and lopinavir/ritonavir on glucose uptake and insulin sensitivity

We read with interest the article by Noor et al. [1] examining the differential effects on glucose metabolism of the combinations of atazanavir/ritonavir versus lopinavir/ritonavir. Their paper deals with an important issue, having both theoretical interest and clinical impact. We think that some comments concerning aspects of the experimental procedure, data analysis and interpretation of the results could be helpful to other readers. The euglycemic hyperinsulinemic clamp is the golden standard for the assessment of insulin sensitivity. This experimental approach requires that the glucose concentration is maintained at a constant level throughout the study [2]. However, in the study by Noor et al.[1], the glucose concentration increased remarkably (up to 100 mg/dl) during the initial portion of the clamp (their fig. 3a), a defect which may influence the clamp-derived estimate of insulin sensitivity. During the clamp, it is assumed that endogenously secreted insulin is inhibited and only peripherally administered insulin contributes to insulin elevation. If the glycemic increase triggered an endogenous insulin response, this likely influenced the degree of inhibition of endogenous glucose production because the acute elevation of the portal insulin level has been shown to have a long-lasting effect on the liver [3]. As a result, the clamp-derived estimate of insulin sensitivity would also be affected. Additional data on the C-peptide would be welcome to verify the time course of endogenous insulin secretion, as a bias cannot otherwise be ruled out. In analyzing the oral glucose tolerance test (OGTT), Noor et al.[1] used plasma glucose and insulin levels to calculate insulin resistance for each time point of the OGTT by means of the homeostasis model assessment (HOMA) (their fig. 3c). That, however, is a misuse of the HOMA method, which has been developed to provide an index of insulin resistance from the concentrations of glucose and insulin measured at the basal steady state [4]. This method cannot be applied to nonsteady-state conditions when insulin and glucose concentrations continuously change. Thus, the authors had no methodological support for calculating the HOMA index at each time point during the OGTT and performing statistical comparisons among groups. In discussing their data obtained in vivo, Noor et al.[1] faced the problem of reconciling a discrepancy between the euglycemic, hyperinsulinemic clamp and OGTT results. Although the clamp revealed a significantly different reduction in insulin sensitivity between atazanavir/ritonavir and lopinavir/ritonavir, the OGTT did not (their table 2). The authors claimed that this discrepancy was due to the fact that the OGTT reflects both liver and peripheral insulin sensitivity, whereas the glucose clamp only reflects the latter component. This argument is questionable for the following reasons. First, a patent contradiction immediately emerges. If the OGTT reflects both liver and peripheral insulin sensitivity, whereas the clamp only reflects the latter, the OGTT would be expected to be more capable than the clamp of detecting differences in insulin sensitivity among the study groups. This contradicts the experimental evidence, which shows the opposite. Second, the claim that the clamp only reflects peripheral insulin sensitivity has no grounds. The index of clamp-based insulin sensitivity used by Noor et al.[1] is the ratio M/I, where M is the exogenous glucose infusion rate and I is the insulin concentration, both measured at the end of the clamp. It is worth emphasizing that the glucose infused during the clamp allows a constant plasma glucose concentration to be maintained because it balances exactly the increase in glucose disappearance (Rd) and the reduction in endogenous glucose production (EGP). Thus, the M-value measures the ability of insulin to stimulate peripheral glucose uptake, as well as to inhibit glucose production (M = ΔRd − ΔEGP, where Δ is the change from pretest level) [5]. In the study by Noor et al.[1], the inhibition of endogenous glucose production could not be assumed to be identical in the study groups because protease-inhibitors are known to affect liver insulin sensitivity [6]. The contribution of glucose uptake can only be isolated from that of endogenous glucose production if a glucose tracer is concurrently infused along with unlabeled glucose [5], but Noor et al.[1] did not use a tracer. It can be concluded that the true reason for the discrepancy between the clamp and OGTT results remains to be elucidated. In conclusion, we hope that the above considerations may prove useful to clinicians in the interpretation of studies assessing the effects of antiretroviral drugs on carbohydrate metabolism using methods such as the euglycemic hyperinsulinemic clamp, the HOMA, or the OGTT.

Pioglitazone Ameliorates Insulin Resistance and Diabetes by Both Adiponectin-dependent and -independent Pathways

Thiazolidinediones have been shown to up-regulate adiponectin expression in white adipose tissue and plasma adiponectin levels, and these up-regulations have been proposed to be a major mechanism of the thiazolidinedione-induced amelioration of insulin resistance linked to obesity. To test this hypothesis, we generated adiponectin knock-out (adipo-/-) ob/ob mice with a C57B/6 background. After 14 days of 10 mg/kg pioglitazone, the insulin resistance and diabetes of ob/ob mice were significantly improved in association with significant up-regulation of serum adiponectin levels. Amelioration of insulin resistance in ob/ob mice was attributed to decreased glucose production and increased AMP-activated protein kinase in the liver but not to increased glucose uptake in skeletal muscle. In contrast, insulin resistance and diabetes were not improved in adipo-/-ob/ob mice. After 14 days of 30 mg/kg pioglitazone, insulin resistance and diabetes of ob/ob mice were again significantly ameliorated, which was attributed not only to decreased glucose production in the liver but also to increased glucose uptake in skeletal muscle. Interestingly, adipo-/-ob/ob mice also displayed significant amelioration of insulin resistance and diabetes, which was attributed to increased glucose uptake in skeletal muscle but not to decreased glucose production in the liver. The serum-free fatty acid and triglyceride levels as well as adipocyte sizes in ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were significantly reduced to a similar degree after 30 mg/kg pioglitazone. Moreover, the expressions of TNFalpha and resistin in adipose tissues of ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were decreased after 30 mg/kg pioglitazone. Thus, pioglitazone-induced amelioration of insulin resistance and diabetes may occur adiponectin dependently in the liver and adiponectin independently in skeletal muscle.

Exercise-Induced Changes in Insulin Action and Glycogen Metabolism in Elderly Adults

Although data suggest that physical activity is associated with decreased insulin resistance, recommendations for exercise training are not specific for age or level of obesity. Therefore, we examined the influence of moderate-intensity (50% of VO2max) exercise training (MI) versus high-intensity (75% of VO2max) exercise training (HI) on insulin-stimulated glucose disposal (ISGD) in elderly individuals. Following medical examinations, 21 overweight (body mass index = 29 +/- 1 kg x m(-2)) elderly (74 +/- 1 yr) subjects were randomized to 1) HI, 2) MI, or a 3) nonexercising control group. Subjects enrolled in HI or MI completed a 12-wk exercise training regimen designed to expend 1000 kcal x wk. ISGD was assessed using a hyperinsulinemic, euglycemic clamp pre- and postintervention. ISGD was corrected for hepatic glucose production (glucose Ra) using a constant rate infusion of [6,6-H2]glucose and determined during the last 30 min of the clamp by subtracting glucose Ra from the exogenous glucose infusion rate. Nonoxidative glucose disposal was calculated using indirect calorimetry. Body composition testing was completed using dual energy x-ray absorptiometry. ISGD increased by approximately 20% with HI (Delta of 1.4 +/- 0.5 mg x kg(-1) FFM.min(-1)). However, ISGD did not change (Delta of -0.4 +/- 0.1 mg x kg(-1) FFM.min(-1)) with MI and was not different (Delta of -0.2 +/- 0.1 mg x kg(-1) FFM.min(-1)) in the control group. Nonoxidative glucose disposal increased with HI (Delta of 1.4 +/- 0.5 mg x kg(-1) FFM.min(-1)), but there was no change in nonoxidative glucose disposal with MI or in the control group. No change in body weight or percentage of body fat was observed in any group. In weight-stable subjects, MI resulted in no change in ISGD, and the improvement in ISGD with HI was completely reliant on improvements in nonoxidative glucose disposal.

Acute, same-day effects of antecedent exercise on counterregulatory responses to subsequent hypoglycemia in type 1 diabetes mellitus

Exercise-induced hypoglycemia can occur within hours after exercise in type 1 diabetes mellitus (T1DM) patients. This study tested the hypothesis that an acute exercise bout causes (within hours) blunted autonomic and metabolic responses to subsequent hypoglycemia in patients with T1DM. Twelve T1DM patients (3 W/9 M) were studied during a single-step, 2-h hyperinsulinemic (572 +/- 4 pmol/l) hypoglycemic (2.8 +/- 0.1 mmol/l) clamp 2 h after either a hyperinsulinemic euglycemic (AM EUG) or hypoglycemic clamp (AM HYPO) or after sitting in a chair with basal insulin infusion (AM CON) or 90 min of moderate-intensity exercise (50% Vo(2 max), AM EX). Both AM HYPO and AM EX significantly blunted epinephrine responses and muscle sympathetic nerve activity responses to subsequent hypoglycemia compared with both control groups. Endogenous glucose production was significantly lower and the exogenous glucose infusion rate needed to maintain the hypoglycemic level was significantly greater during subsequent hypoglycemia in AM EX vs. CON. Rate of glucose disposal (Rd) was significantly reduced following AM HYPO. In summary, within 2.5 h, both moderate-intensity AM EX and AM HYPO blunted key autonomic counterregulatory responses. Despite this, glucose Rd was reduced during afternoon hypoglycemia following morning hypoglycemia, indicating posthypoglycemic insulin resistance. After morning exercise, endogenous glucose production was blunted, but glucose Rd was maintained during afternoon hypoglycemia, thereby indicating reduced metabolic defenses against hypoglycemia. These data suggest that exercise-induced counterregulatory failure can occur very rapidly, increasing the risk for hypoglycemia in T1DM within hours.

Endothelial function, insulin action and cardiovascular risk factors in young healthy adult offspring of parents with Type 2 diabetes: effect of vitamin E in a randomized double‐blind, controlled clinical trial

Endothelial dysfunction, insulin resistance and oxidative stress are believed to be central and associated mechanisms in atherogenesis. We aimed to determine the effect of the antioxidant vitamin E on endothelial function, insulin action and cardiovascular risk markers in young healthy adult offspring of parents with Type 2 diabetes. Healthy, glucose-tolerant adults (18-38 years), 14 (12 male/2 female) with at least one parent with Type 2 diabetes, and 14 (12 male/2 female) subjects with no family history of diabetes (controls) were studied. Insulin action was assessed by euglycaemic hyperinsulinaemic clamp (1 mU/kg/min). Endothelial function was assessed by forearm blood flow (FBF) responses to intra-brachial artery infusions of acetylcholine (ACh) (endothelium-dependent vasodilation), sodium nitroprusside (SNP) (endothelium-independent vasodilation) and N(G)-monomethyl L-arginine (LNMMA) (nitric oxide synthase inhibition). Thirteen offspring (18-38 years, 11 male/2 female, BMI < 30 kg/m2) completed a randomized, double-blind, crossover trial (12 weeks vitamin E 800 IU/day or placebo, 6-week washout). Exogenous glucose infusion rates to maintain euglycaemia were positively associated with response to acetylcholine in offspring (r = 0.61, P < 0.05), and were linked with triglycerides. Vitamin E had no effect on endothelial function, insulin action or cardiovascular risk markers in healthy adult offspring of parents with Type 2 diabetes. Our results support a positive association between insulin action and endothelial-dependent vasodilation in young healthy adult offspring of parents with Type 2 diabetes, but indicate no effect of vitamin E on these parameters.

Correlation between insulin resistance and intramyocellular lipid levels in rats

Increased intramyocellular lipid (IMCL) content has been proposed as biomarker for insulin resistance (IR). An inverse correlation between IMCL and insulin sensitivity (IS) was found in nonathletic humans, whereas in animal models only a few validation studies have been performed. The aim of this study was to investigate the interrelation between IS indices determined by the glucose clamp technique (glucose disposal (GD), exogenous glucose infusion rates (GIR)) and IMCL content in the tibialis (TIB) and the soleus (SOL) muscle obtained by magnetic resonance spectroscopy in different rat models of IR. Diet-induced insulin-resistant Wistar rats as well as genetic disease models (ZDF rats) were used. In both muscles, elevated IMCL correlated with an impaired IS in all models of IR. The correlation of IMCL with both parameters for IS was comparable in TIB and SOL. The best fit between IMCL and IS was obtained using TIB and GIR data (r = -0.69, P < 0.001). Diabetic male ZDF rats exhibited comparatively low IMCL levels due to their catabolic state: exclusion of this group improved r. In summary, IMCL, especially in TIB, is a valid biomarker for IS in various rat models of IR with the advantage of a fast repeatable noninvasive measurement in individual animals.

Changes in aquaporin 1 expression affect amniotic fluid volume

STEPHANIE MANN, NATALIA DVORAK, ROBERT TAYLOR, Phoenix Integrated Residency in Ob/Gyn, Obstetrics and Gynecology, Phoenix, Arizona, University of California, San Francisco, Obstetrics, Gynecology and Reproductive Sciences, San Francisco, California OBJECTIVE: Recent work from our laboratory has demonstrated the presence of aquaporin (AQP) water channels in fetal membranes from pregnancies with normal amniotic fluid (AF) volume. The objective of this study was to investigate changes in AQP 1 mRNA expression from fetal membranes of pregnancies with polyhydramnios and oligohydramnios. STUDY DESIGN: Placentas from term pregnancies (37-40 wks) were collected from women who presented with intact membranes and one of the following: (1) idiopathic oligohydramnios (AFI !5.0 cm); (2) polyhydramnios (AFI >24.0 cm); and (3) normal amount AF (AFI >5.0 cm and!24.0 cm). The membranes (amnion and chorion) directly overlying the placenta and the free floating reflected membranes were sampled (total of four samples from each placenta). RNA was isolated from the amnion and chorion of each region. Quantitative RT-PCR was used to compare expression of AQP1 mRNA in the membranes collected from the above pregnancies. Statistical analysis was performed with a t test. P ! .05 was considered signficant. RESULTS: As shown in the figure, AQP1 mRNA expression is increased in the reflected amnion from pregnancies with idiopathic polyhydramnios and decreased in the reflected amnion and chorion from pregnancies with oligohydramnios. CONCLUSION: The expression of the water channel AQP1 is altered in the reflected fetal membranes. These results suggests that there is an adaptive response by the fetal membranes in situations of either decreased or increased AF volume to prevent excessive loss or accumulation of fluid, respectively. We speculate that therapies focused on regulating AQP1 expression may be useful for treating oligohydramnios and polyhydramnios. 458 PERINATAL GLUCOSE TOLERANCE AFTER INTRAUTERINE GROWTH RESTRICTION IN THE LATE-GESTATION OVINE FETUS PHILIPPE DERUELLE, IVA GUEORGUIEVA, BERENGERE SICOT DE JENLIS, SOPHIE JAILLARD, JACQUES WEILL, VERONIQUE DEBARGE, LAURENT STORME, CHRU de Lille, Lille, France, CHRU de Lille, Pediatric endocrinology unit, Lille, France, CHRU de Lille, Department of perinatology, Lille, France, CHRU de Lille, France, Department of perinatology, Lille, France OBJECTIVE: Newborns with Intrauterine-Growth Restriction (IUGR) are at increased risk to develop a metabolic syndrome later in life, namely obesity, cardiovascular disease, impaired glucose tolerance. Whereas these facts have been largely studied during childhood or adult life, little is known about the consequences of IUGR on glucose tolerance during the perinatal period. The purpose of this study was to determine whether chronic placental embolization in the late gestation ovine fetus induce insulin resistance during the perinatal period. STUDY DESIGN: IUGR was induced by umbilico-placental embolization during late gestation in chronically catheterized sheep. Umbilico-placental embolization was performed between 130 and 140 d of gestation (terme = 147 d) during which fetuses were hypoxemic relative to controls. Euglycemic, hyperinsulinemic glucose clamp experiments were performed in utero and during the first three weeks after birth in order to measure the effect of fetal insulin concentration on fetal glucose uptake at a constant glucose concentration. Fetal coricotropin, cortisol and catecholamines concentrations were measured daily. RESULTS: Chronic placental embolization produced asymmetrically IUGR fetuses and increased vascular resistance in umbilical artery (P ! .05). The exogenous glucose infusion rate necessary to maintain constant glycemia was significantly lower in IUGR relative to control fetuses at 140 d of gestation (IUGR vs. control, 2.5 G .5 mg/kg/min and 5.0 G 0.5 mg/kg/min, P ! .05) and 7 days after birth (IUGR vs. control, 3.5 G .7 mg/kg/min and 5.7 G 1.4 mg/kg/ min, P ! .05). Glucose clamps were similar between groups at 2 and 3 weeks after birth. Cortisol levels were similar between the two groups. In response to chronic fetal hypoxemia, there was a progressive increased in baseline fetal plasma epinephrine, norepinephrine and dopamine concentrations (P ! .01). CONCLUSION: We concluded that chronic fetal hypoxemia induces insulin resistance during the perinatal period. We speculate that this change could be related to an increase in fetal catecholamines levels.

Effects of low and moderate antecedent exercise on counterregulatory responses to subsequent hypoglycemia in type 1 diabetes.

Antecedent moderate-intensity exercise has been shown to blunt autonomic, neuroendocrine, and metabolic counterregulatory responses to subsequent hypoglycemia in nondiabetic individuals. The aims of the current study were to determine 1) whether this occurs in type 1 diabetic patients and 2) whether the degree of blunting is dependent on exercise intensity. Twenty-seven type 1 diabetic patients (13 women and 14 men) were studied during a single-step, 2-h hyperinsulinemic (9 pmol x kg(-1) x min(-1))-hypoglycemic (approximately 2.8 mmol/l) clamp 1 day after two 90-min exercise bouts at 30% (n = 11) or at 50% (n = 11) Vo(2max) or after no prior stress (control subjects, n = 25). After prior exercise at both 30 and 50% Vo(2max), epinephrine (1,959 +/- 553 and 1,528 +/- 424 vs. 3,420 +/- 424 pmol/l, respectively; P < 0.05) and pancreatic polypeptide (97 +/- 32 and 98 +/- 8 vs. 223 +/- 32 pmol/l, respectively; P < 0.05) responses to subsequent hypoglycemia were significantly lower compared with those of control subjects. Endogenous glucose production was significantly lower, while glucose utilization and, consequently, the exogenous glucose infusion rate needed to maintain hypoglycemia were significantly greater after both exercise intensities compared with that of control subjects. Muscle sympathetic nerve activity was significantly reduced by prior exercise of both intensities at baseline (16 +/- 4 and 22 +/- 4 vs. 31 +/- 3 bursts/min) and during hypoglycemia (22 +/- 4 and 27 +/- 5 vs. 41 +/- 3 bursts/min) compared with that of control subjects (P < 0.05). Total hypoglycemic symptoms were also significantly lower (P < 0.05) in both exercise groups compared with the control group. In summary, repeated episodes of prolonged exercise of both low and moderate intensities blunted key autonomic (epinephrine and pancreatic polypeptide) and metabolic (endogenous glucose production and peripheral glucose uptake) counterregulatory responses to next-day hypoglycemia in type 1 diabetes.

Determination of reference range values indicative of glucose metabolism and insulin resistance by use of glucose clamp techniques in horses and ponies.

To acquire reference range values indicative of glucose metabolism by use of the hyperglycemic clamp technique in healthy horses and evaluate the usefulness of the euglycemic hyperinsulinemic clamp technique in healthy horses and ponies. Dutch Warmblood horses and 4 Shetland ponies. The hyperglycemic clamp technique was used for quantification of the sensitivity of beta cells to exogenous glucose infusion in horses. The euglycemic hyperinsulinemic clamp technique was used to determine the sensitivity and responsiveness of tissues to exogenous insulin in horses and ponies. During the hyperglycemic clamp technique, the mean amount of glucose metabolized (M) in horses was 0.011 +/- 0.0045 mmol/kg x min(-1) (95% confidence interval [CI], 0.0018 to 0.020 mmol/kg x min(-1); range, 0.000035 to 0.021 mmol/kg x min(-1)) and the mean M value-to-plasma insulin concentration (I) ratio (ie, mmol of glucose/kg x min(-1) per pmol of insulin/L x 100) was 0.017 +/- 0.016 (95% CI, -0.014 to 0.049; range, 0.000025 to 0.055). During the euglycemic hyperinsulinemic clamp technique, the mean M value was 0.014 +/- 0.0055 mmol/kg x min(-1) (95% CI, 0.0026 to 0.025 mmol/kg x min(-1); range, 0.0042 to 0.023 mmol/kg x min(-1)) in horses and 0.0073 +/- 0.0020 mmol/kg x min(-1) (95% CI, 0.0034 to 0.011 mmol/kg x min(-1); range, 0.0049 to 0.011 mmol/kg x min(-1)) in ponies. The M value was significantly lower in ponies than in horses, whereas the M:I ratios were not significantly different between horses and ponies. Glucose clamp techniques offer good methods to investigate glucose metabolism in horses and ponies. A higher degree of insulin resistance was found in ponies, compared with Dutch Warmblood horses.