Epinephrine inhibits insulin-stimulated muscle glucose transport

The role of exercise and hypoxia on glucose transport and regulation

Muscle glucose transport activity increases with an acute bout of exercise, a process that is accomplished by the translocation of glucose transporters to the plasma membrane. This process remains intact in the skeletal muscle of individuals with insulin resistance and type 2 diabetes mellitus (T2DM). Exercise training is, therefore, an important cornerstone in the management of individuals with T2DM. However, the acute systemic glucose responses to carbohydrate ingestion are often augmented during the early recovery period from exercise, despite increased glucose uptake into skeletal muscle. Accordingly, the first aim of this review is to summarize the knowledge associated with insulin action and glucose uptake in skeletal muscle and apply these to explain the disparate responses between systemic and localized glucose responses post-exercise. Herein, the importance of muscle glycogen depletion and the key glucoregulatory hormones will be discussed. Glucose uptake can also be stimulated independently by hypoxia; therefore, hypoxic training presents as an emerging method for enhancing the effects of exercise on glucose regulation. Thus, the second aim of this review is to discuss the potential for systemic hypoxia to enhance the effects of exercise on glucose regulation.

Acute and chronic metabolic effects of carvedilol in high-fructose, high-fat diet-fed mice: implication of β-arrestin2 pathway

We aimed to investigate the acute and chronic effects of carvedilol on insulin resistance in high-fructose, high-fat diet (HFrHFD) - fed mice and the implication of the β-arrestin2 pathway. The acute effect of carvedilol (10 mg/kg, i.p.) on glucose tolerance and hepatic lipid signaling in normal and insulin resistant mice was investigated. Then, the chronic effect of carvedilol on insulin resistance and dyslipidemia in HFrHFD-fed mice was examined. Changes in β-arrestin2 and its downstream signals in liver, skeletal muscle, and adipose tissue were measured. This involved measuring phosphatidylinositol 4,5-bisphosphate (PIP2) and diacylglycerol (DAG) levels and protein kinase B (AKT) activity. Carvedilol acutely reduced fasting blood glucose levels in both normal and insulin resistant mice without significantly affecting the glucose tolerance. These acute effects were associated with increased hepatic PIP2 but decreased hepatic DAG levels. Chronic administration of carvedilol significantly ameliorated insulin resistance and dyslipidemia in HFrHFD-fed mice. These chronic effects were associated with increased β-arrestin2, PIP2, and AKT activity levels but decreased DAG levels in the classical insulin target tissues. In conclusion, carvedilol acutely maintains glucose homeostasis and chronically ameliorates insulin resistance and dyslipidemia in HFrHFD-fed mice. The insulin sensitizing effects of carvedilol are highly correlated with the upregulation of β-arrestin2 pathway.

GLP-1 Receptor: A New Target for Sepsis

Patients with sepsis often exhibit hyperglycemia, which increases mortality. glucagon-like peptide-1 receptor agonists (GLP-1RAs) not only regulate blood glucose homeostasis but also improve organ dysfunction, regulate immunity, and control inflammation and other functions in patients with sepsis. Here, we review the possible application of GLP-1RAs in sepsis, to provide a new perspective for the clinical diagnosis and treatment of patients with sepsis complicated with stress hyperglycemia.

Stress Hyperglycemia in Children and Adolescents as a Prognostic Indicator for the Development of Type 1 Diabetes Mellitus

Hyperglycemia is a common manifestation in the course of severe disease and is the result of acute metabolic and hormonal changes associated with various factors such as trauma, stress, surgery, or infection. Numerous studies demonstrate the association of adverse clinical events with stress hyperglycemia. This article briefly describes the pathophysiological mechanisms which lead to hyperglycemia under stressful circumstances particularly in the pediatric and adolescent population. The importance of prevention of hyperglycemia, especially for children, is emphasized and the existing models for the prediction of diabetes are presented. The available studies on the association between stress hyperglycemia and progress to type 1 diabetes mellitus are presented, implying a possible role for stress hyperglycemia as part of a broader prognostic model for the prediction and prevention of overt disease in susceptible patients.

Hot water immersion acutely increases postprandial glucose concentrations

Chronic hot water immersion (HWI) confers health benefits, including a reduction in fasting blood glucose concentration. Here we investigate acute glycemic control immediately after HWI. Ten participants (age: 25 ± 6 years, body mass: 84 ± 14 kg, height 1.85 ± 0.09 m) were immersed in water (39°C) to the neck (HWI) or sat at room temperature (CON) for 60 min. One hour afterward they underwent an oral glucose tolerance test (OGTT), with blood collected before and after HWI/CON and during the 2 h OGTT. Glucose incremental area under the curve (iAUC) during the OGTT was higher for HWI (HWI 233 ± 88, CON 156 ± 79 mmol·L^-1 ·2 h, P = 0.02). Insulin iAUC did not differ between conditions (HWI 4309 ± 3660, CON 3893 ± 3031 mU·L^-1 ·2 h, P = 0.32). Core temperature increased to 38.6 ± 0.2°C during HWI, but was similar between trials during the OGTT (HWI 37.0 ± 0.2, CON 36.9 ± 0.4°C, P = 0.34). Directly following HWI, plasma average adrenaline and growth hormone concentrations increased 2.7 and 10.7-fold, respectively (P < 0.001). Plasma glucagon-like peptide-1, peptide YY, and acylated ghrelin concentrations were not different between trials during the OGTT (P > 0.11). In conclusion, HWI increased postprandial glucose concentration to an OGTT, which was accompanied by acute elevations of stress hormones following HWI. The altered glycemic control appears to be unrelated to changes in gut hormones during the OGTT.

Adverse effects of noise stress on glucose homeostasis and insulin resistance in Sprague-Dawley rats

Noise pollution remains a pervasive health hazard that people encounter especially in large commercial metropolis and has been implicated in many adverse non-auditory health conditions such as hypertension, atherosclerosis, vascular (endothelial) dysfunction and metabolic disorders. There is a growing body of evidence showing that chronic noise exposure is associated with an increased risk of hypercholesterol, adiposity and development of type 2 diabetes. The present study investigated the effect of noise stress on parameters of glucose homeostasis in male rats and possible recovery after noise cessation. Twenty-four (24) adult male Sprague-Dawley rats were designated into four groups (n = 6 per group). All rats except the control group were exposed to 95dB noise using a noise generator for 28 consecutive days. A group of rats was investigated immediately after 28 days of noise exposure (NE28), while others were left to recover from noise stress for 7 days (NER7) or 14 days (NER14). OGTT and ITT were performed using standard methods. Plasma levels of triglyceride (TRIG), total cholesterol (CHOL), low density lipoprotein (LDL) and high-density lipoprotein (HDL) were determined. Serum level of insulin, corticosterone (CORT) and corticosterone-releasing-factor (CRF) were determined using ELISA. Homeostasis model assessment-insulin resistance (HOMA-IR) and glycogen content in liver as well as gastrocnemius muscle were also determined.

Although glucose tolerance remained unchanged in the noise-exposed groups, insulin sensitivity was however significantly reduced compared with control. There was significant increase (P < 0.05) in the level of CHOL, LDL and HDL. Noise also increased (P < 0.05) both insulin and CORT levels; and elicited a higher HOMA-IR index in NE28 rats. Hepatic and myocytic glycogen content were lower (P < 0.05) in NE28 rats relative to control. The reported changes above were reversed following a 14-day noise withdrawal period. Noise-induced insulin resistance may result from dysregulation of the stress axis and appears to be reversible with noise cessation.

Effects of Epinephrine, Detomidine, and Butorphanol on Assessments of Insulin Sensitivity in Mares

Sympathoadrenal stimulation may perturb results of endocrine tests performed on fractious horses. Sedation may be beneficial; however, perturbation of results may preclude useful information. Four experiments were designed to 1) determine the effects of epinephrine on insulin response to glucose (IR2G), 2) assess the effects of detomidine (DET), alone or combined with butorphanol (DET/BUT), on IR2G and glucose response to insulin (GR2I), and 3) assess the effects of BUT alone on IR2G. In Experiment 1, mares were administered saline or epinephrine (5 μg/kg BW) immediately before infusion of glucose (100 mg/kg BW). Glucose stimulated (P < .05) insulin release in controls at 5 minutes that persisted through 30 minutes; insulin was suppressed (P < .05) by epinephrine from 5 to 15 minutes, rising gradually through 30 minutes. Experiments 2 (IR2G) and 3 (GR2I) were conducted as triplicated 3 × 3 Latin squares with the following treatments: saline (SAL), DET, and DET/BUT (all administered at .01 mg/kg BW). Glucose stimulated (P < .05) insulin release that persisted through 30 minutes in SAL mares; DET and DET/BUT severely suppressed (P < .0001) the IR2G. Sedation did not affect resting glucose and had inconsistent effects on the GR2I when mares were treated with 50 mIU/kg BW recombinant human insulin. Butorphanol had no effect on IR2G. In conclusion, adrenergic agonists severely suppress the IR2G and cannot be used for sedation for this test. The use of DET did not alter the GR2I, and therefore may be useful for conducting this test in fractious horses.

Therapeutic Effects of Endogenous Incretin Hormones and Exogenous Incretin-Based Medications in Sepsis

BACKGROUND

Sepsis, a complex disorder characterized by a dysregulated immune response to an inciting infection, affects over one million Americans annually. Dysglycemia during sepsis hospitalization confers increased risk of organ dysfunction and death, and novel targets for the treatment of sepsis and maintenance of glucose homeostasis are needed. Incretin hormones are secreted by enteroendocrine cells in response to enteral nutrients and potentiate insulin release from pancreatic β cells in a glucose-dependent manner, thereby reducing the risk of insulin-induced hypoglycemia. Incretin hormones also reduce systemic inflammation in preclinical studies, but studies of incretins in the setting of sepsis are limited.

METHODS

In this bench-to-bedside mini-review, we detail the evidence to support incretin hormones as a therapeutic target in patients with sepsis. We performed a PubMed search using the medical subject headings "incretins," "glucagon-like peptide-1," "gastric inhibitory peptide," "inflammation," and "sepsis."

RESULTS

Incretin-based therapies decrease immune cell activation, inhibit proinflammatory cytokine release, and reduce organ dysfunction and mortality in preclinical models of sepsis. Several small clinical trials in critically ill patients have suggested potential benefit in glycemic control using exogenous incretin infusions, but these studies had limited power and were performed in mixed populations. Further clinical studies examining incretins specifically in septic populations are needed.

CONCLUSIONS

Targeting the incretin hormone axis in sepsis may provide a means of not only promoting euglycemia in sepsis but also attenuating the proinflammatory response and improving clinical outcomes.

Chlorpyrifos Induces Metabolic Disruption by Altering Levels of Reproductive Hormones

Chlorpyrifos (CPF) is a widely used organophosphorus pesticide and detected frequently in fruits, vegetables, as well as in urine and blood in humans. Studies have suggested that CPF can induce metabolic disruption, such as type-2 diabetes mellitus and changed body weight. The main mechanisms are based on oxidative damage, fatty-acid synthesis, and lipid peroxidation. Studies have also shown that CPF can change reproductive hormone (RH) levels. CPF might result in metabolic disorders through altered RH levels. Here, we review the studies showing that CFP causes metabolic disruption. Then, we present the studies showing that CFP changes RH levels. Finally, we discuss a potential pathway of how CPF elicits metabolic disruption.

NLRP3 inflammasome as a potential treatment in ischemic stroke concomitant with diabetes

The NLRP3 (nucleotide-binding oligomerization domain-like receptor [NLR] family pyrin domain-containing 3) inflammasome is a member of the NLR family of innate immune cell sensors. These are crucial regulators of cytokine secretions, which promote ischemic cell death and insulin resistance. This review summarizes recent progress regarding the NLRP3 inflammasome as a potential treatment for ischemic stroke in patients with diabetes, two complicated diseases that often occur together. Stroke worsens glucose metabolism abnormalities, and the outcomes after stroke are more serious for diabetic patients compared with those without diabetes. Inflammation contributes to organ injury after ischemic stroke and diabetes. Recent research has focused on inhibiting the activation of inflammasomes and thus reducing the maturation of proinflammatory cytokines such as interleukin (IL)-1β and IL-18. Studies suggest that inhibition of NLRP3 prevents or alleviates both ischemic stroke and diabetes. Targeting against the assembly and activity of the NLRP3 inflammasome is a potential and novel therapy for inflammasome-associated diseases, including ischemic stroke concomitant with diabetes.

Pancreatic function and histoarchitecture in Wistar rats following chronic exposure to Bushfire®: the mitigating role of zinc

Objectives To assess the toxicopathologic effects of chronic exposure to the glyphosate-based herbicide Bushfire® on the pancreas of Wistar rats and the protective role of zinc. Methods We exposed the rats to daily doses of 14.4 to 750 mg/kg body weight of the glyphosate-based herbicide Bushfire® and to 50 or 100 mg/kg zinc, and measured blood glucose levels and serum insulin levels. Tissue samples were evaluated for histopathological alterations. Results Levels of both blood glucose and serum insulin increased in glyphosate-exposed rats, and moderate to severe degenerative changes were observed in both glandular pancreatic acinar cells and islets of Langerhans in all rats exposed to glyphosate. These effects were prevented by pretreatment with zinc. Conclusion Chronic exposure to glyphosate can alter pancreatic function and histoarchitecture, but zinc supplementation can mitigate these toxicopathologic effects.

Adeno-associated virus-mediated expression of myostatin propeptide improves the growth of skeletal muscle and attenuates hyperglycemia in db/db mice

Inhibition of myostatin, a negative growth modulator for muscle, can functionally enhance muscle mass and improve glucose and fat metabolism in myostatin propeptide (MPRO) transgenic mice. This study was to investigate whether myostatin inhibition by adeno-associated virus (AAV)-mediated gene delivery of MPRO could improve muscle mass and achieve therapeutic effects on glucose regulation and lipid metabolism in the db/db mice and the mechanisms involved in that process. Eight-week-old male db/db mice were administered saline, AAV-GFP and AAV-MPRO/Fc vectors and monitored random blood glucose levels and body weight for 36 weeks. Body weight gain was not different during follow-up among the groups, but AAV-MPRO/Fc vectors resulted high level of MPRO in the blood companied by an increase in skeletal muscle mass and muscle hypertrophy. In addition, AAV-MPRO/Fc-treated db/db mice showed significantly lower blood glucose and insulin levels and significantly increased glucose tolerance and insulin sensitivity compared with the control groups (P<0.05). Moreover, these mice exhibited lower triglyceride (TG) and free fatty acid (FFA) content in the skeletal muscle, although no difference was observed in fat pad weights and serum TG and FFA levels. Finally, AAV-MPRO/Fc-treated mice had enhanced insulin signaling in the skeletal muscle. These data suggest that AAV-mediated MPRO therapy may provide an important clue for potential clinical applications to prevent type II diabetes, and these studies confirm that MPRO is a therapeutic target for type II diabetes.

Exercise Intensity Modulates Glucose-Stimulated Insulin Secretion when Adjusted for Adipose, Liver and Skeletal Muscle Insulin Resistance

Little is known about the effects of exercise intensity on compensatory changes in glucose-stimulated insulin secretion (GSIS) when adjusted for adipose, liver and skeletal muscle insulin resistance (IR). Fifteen participants (8F, Age: 49.9±3.6yr; BMI: 31.0±1.5kg/m²; VO₂peak: 23.2±1.2mg/kg/min) with prediabetes (ADA criteria, 75g OGTT and/or HbA_1c) underwent a time-course matched Control, and isocaloric (200kcal) exercise at moderate (MIE; at lactate threshold (LT)), and high-intensity (HIE; 75% of difference between LT and VO₂peak). A 75g OGTT was conducted 1 hour post-exercise/Control, and plasma glucose, insulin, C-peptide and free fatty acids were determined for calculations of skeletal muscle (1/Oral Minimal Model; SM_IR), hepatic (HOMA_IR), and adipose (ADIPOSE_IR) IR. Insulin secretion rates were determined by deconvolution modeling for GSIS, and disposition index (DI; GSIS/IR; DI_SMIR, DI_HOMAIR, DI_ADIPOSEIR) calculations. Compared to Control, exercise lowered SM_IR independent of intensity (P<0.05), with HIE raising HOMA_IR and ADIPOSE_IR compared with Control (P<0.05). GSIS was not reduced following exercise, but DI_HOMAIR and DI_ADIPOSEIR were lowered more following HIE compared with Control (P<0.05). However, DI_SMIR increased in an intensity based manner relative to Control (P<0.05), which corresponded with lower post-prandial blood glucose levels. Taken together, pancreatic insulin secretion adjusts in an exercise intensity dependent manner to match the level of insulin resistance in skeletal muscle, liver and adipose tissue. Further work is warranted to understand the mechanism by which exercise influences the cross-talk between tissues that regulate blood glucose in people with prediabetes.

Chromium chloride increases insulin-stimulated glucose uptake in the perfused rat hindlimb

AIM

To determine the effect of chromium chloride (CrCl3 ) on healthy skeletal muscle glucose uptake in the absence and presence of submaximal insulin using the rat hindlimb perfusion technique.

METHODS

Sprague-Dawley rats were randomly assigned to an experimental group: basal (Bas), chromium chloride (Cr), submaximal insulin (sIns) or chromium chloride plus submaximal insulin (Cr-sIns).

RESULTS

Insulin significantly increased [H(3)]-2 deoxyglucose (2-DG) uptake in the gastrocnemius muscles. Additionally, Cr-sIns displayed greater rates of 2-DG uptake than sIns (Cr-sIns 6.86 ± 0.74 μmol g h(-1) vs. sIns 4.83 ± 0.42 μmol g h(-1)). There was no difference between Cr and Bas treatment groups. It has been speculated that chromium works to increase glucose uptake by increasing insulin signalling. We found that Akt and AS160 phosphorylation was increased in the sINS treatment group, while chromium treatment had no additional effect on Akt or AS160 phosphorylation in the absence or presence of insulin. Cr-sIns significantly increased plasma membrane GLUT4 concentration above that of sIns (Cr-sIns 72.22 ± 12.7%, sIns 53.4 ± 6.1%), but in the absence of insulin, chromium had no effect.

CONCLUSION

Exposure of healthy skeletal muscle to chromium may increase skeletal muscle insulin-stimulated GLUT4 translocation and glucose uptake. However, these effects do not appear to result from enhanced insulin signalling proximal to AS160.

Autonomic blockade improves insulin sensitivity in obese subjects

Obesity is an important risk factor for the development of insulin resistance. Initial compensatory mechanisms include an increase in insulin levels, which are thought to induce sympathetic activation in an attempt to restore energy balance. We have previously shown, however, that sympathetic activity has no beneficial effect on resting energy expenditure in obesity. On the contrary, we hypothesize that sympathetic activation contributes to insulin resistance. To test this hypothesis, we determined insulin sensitivity using a standard hyperinsulinemic euglycemic clamp protocol in obese subjects randomly assigned in a crossover design 1 month apart to receive saline (intact day) or trimetaphan (4 mg/min IV, autonomic blocked day). Whole-body glucose uptake (MBW in mg/kg per minute) was used as index of maximal muscle glucose use. During autonomic blockade, we clamped blood pressure with a concomitant titrated intravenous infusion of the nitric oxide synthase inhibitor N-monomethyl-L-arginine. Of the 21 obese subjects (43±2 years; 35±2 kg/m(2) body mass index) studied, 14 were insulin resistant; they were more obese, had higher plasma glucose and insulin, and had higher muscle sympathetic nerve activity (23.3±1.5 versus 17.2±2.1 burst/min; P=0.03) when compared with insulin-sensitive subjects. Glucose use improved during autonomic blockade in insulin-resistant subjects (MBW 3.8±0.3 blocked versus 3.1±0.3 mg/kg per minute intact; P=0.025), with no effect in the insulin-sensitive group. These findings support the concept that sympathetic activation contributes to insulin resistance in obesity and may result in a feedback loop whereby the compensatory increase in insulin levels contributes to greater sympathetic activation.

Beta2-adrenoceptor stimulation has no effect on skeletal muscle glucose uptake

INTRODUCTION

Blockade of the β-adrenergic receptor induces insulin resistance and chronic β-adrenoceptor stimulation improves insulin sensitivity in animals. We tested whether acute β2-adrenoceptor stimulation increased insulin-induced glucose uptake in human forearm skeletal muscle.

MATERIALS AND METHODS

During a hyperinsulinemic euglycemic clamp procedure, forearm glucose uptake was calculated by multiplying the arteriovenous glucose gradient and forearm blood flow before and during local infusion of the β2-adrenoceptor salbutamol into the brachial artery.

CONCLUSIONS

β2-Adrenergic stimulation had no effect on insulin-stimulated glucose uptake in human forearm skeletal muscle.

Effects of intravenous lipopolysaccharide infusion on glucose and insulin dynamics in horses with equine metabolic syndrome

OBJECTIVE

To test the hypothesis that glucose and insulin dynamics during endotoxemia differ between healthy horses and horses with equine metabolic syndrome (EMS).

ANIMALS

6 healthy adult mares and 6 horses with EMS.

PROCEDURES

Each horse randomly received an IV infusion of lipopolysaccharide (20 ng/kg [in 60 mL of sterile saline {0.9% NaCl} solution]) or saline solution, followed by the other treatment after a 7-day washout period. Baseline insulin-modified frequently sampled IV glucose tolerance tests were performed 27 hours before and then repeated at 0.5 and 21 hours after infusion. Results were assessed via minimal model analysis and area under the curve values for plasma glucose and serum insulin concentrations.

RESULTS

Lipopolysaccharide infusion decreased insulin sensitivity and increased area under the serum insulin concentration curve (treatment × time) in both healthy and EMS-affected horses, compared with findings following saline solution administration. The magnitude of increase in area under the plasma glucose curve following LPS administration was greater for the EMS-affected horses than it was for the healthy horses. Horses with EMS that received LPS or saline solution infusions had decreased insulin sensitivity over time.

CONCLUSIONS AND CLINICAL RELEVANCE

Glucose and insulin responses to endotoxemia differed between healthy horses and horses with EMS, with greater loss of glycemic control in EMS-affected horses. Horses with EMS also had greater derangements in glucose and insulin homeostasis that were potentially stress induced. It may therefore be helpful to avoid exposure of these horses to stressful situations.

A therapeutic approach to hyperglycaemia in the setting of acute myocardial infarction: spotlight on glucagon-like peptide 1

Patients with acute myocardial infarction (AMI) frequently have abnormalities of glucose metabolism and insulin resistance, both of which are associated with a poor outcome. Glucagon-like peptide 1 (GLP-1) is a naturally occurring incretin with both insulinotropic and insulinomimetic properties which not only controls glucose levels but also has potential beneficial actions on the ischaemic and failing heart. In this review we highlight the underlying pathophysiological mechanisms for the development of hyperglycaemia in AMI, speculate on the potential relationship between GLP-1 and sphingosine-1-phosphate, and review the literature on the role of GLP-1 as an important approach to treating hyperglycaemia in the setting of AMI.

Sympathetic inhibition attenuates hypoxia induced insulin resistance in healthy adult humans

Acute exposure to hypoxia decreases insulin sensitivity in healthy adult humans; the mechanism is unclear, but increased activation of the sympathetic nervous system may be involved. We have investigated the hypothesis that short-term sympathetic inhibition attenuates hypoxia induced insulin resistance. Insulin sensitivity (via the hyperinsulinaemic euglycaemic clamp) was determined in 10 healthy men (age 23 ± 1 years, body mass index 24.2 ± 0.8 kg m⁻² (means ± SEM)), in a random order, during normoxia (FIO₂ =0.21), hypoxia (FIO₂ =0.11), normoxia and sympathetic inhibition (via 48 h transdermal administration of the centrally acting α2-adrenergic receptor agonist, clonidine), and hypoxia and sympathetic inhibition.Oxyhaemoglobin saturation (pulse oximetry) was decreased (P<0.001) with hypoxia (63 ± 2%) compared with normoxia (96 ± 0%), and was unaffected by sympathetic inhibition (P>0.25). The area under the noradrenaline curve (relative to the normoxia response) was increased with hypoxia (137 ± 13%; P =0.02); clonidine prevented the hypoxia induced increase (94 ± 14%; P =0.43). The glucose infusion rate (adjusted for fat free mass and circulating insulin concentration) required to maintain blood glucose concentration at 5 mmol l⁻¹ during administration of insulin was decreased in hypoxia compared with normoxia (225 ± 23 vs. 128 ± 30 nmol (kg fat free mass)⁻¹ pmol l⁻¹ min⁻¹; P =0.03), and unchanged during normoxia and sympathetic inhibition (219 ± 19; P =0.86) and hypoxia and sympathetic inhibition (169 ± 23; P =0.23). We conclude that short-term sympathetic inhibition attenuates hypoxia induced insulin resistance.

Glucose metabolism during the early "flow phase" after burn injury

BACKGROUND

Burn injury (BI) is associated with insulin resistance (IR) and hyperglycemia which complicate clinical management. We investigated the impact of BI on glucose metabolism in a rabbit model of BI using a combination of positron emission tomography (PET) and stable isotope studies under euglycemic insulin clamp (EIC) conditions.

MATERIALS AND METHODS

Twelve male rabbits were subjected to either full-thickness BI (B) or sham burn. An EIC condition was established by constant infusion of insulin, concomitantly with a variable rate of dextrose infusion 3 d after treatment. PET imaging of the hind limbs was conducted to determine the rates of peripheral O(2) and glucose utilization. Each animal also received a primed constant infusion of [6,6-(2)H(2)] glucose to determine endogenous glucose production.

RESULTS

The fasting blood glucose in the burned rabbits was higher than that in the sham group. Under EIC conditions, the sham burn group required more exogenous dextrose than the B group to maintain blood glucose at physiological levels (22.2 ± 2.6 versus 13.3 ± 2.9 mg/min, P < 0.05), indicating a state of IR. PET imaging demonstrated that the rates of O(2) consumption and (18)F 2-fluoro-2-deoxy-D-glucose utilization by skeletal muscle remained at similar levels in both groups. Hepatic gluconeogenesis determined by the stable isotope tracer study was found significantly increased in the B group.

CONCLUSIONS

These findings demonstrated that hyperglycemia and IR develop during the early "flow phase" after BI. Unsuppressed hepatic gluconeogenesis, but not peripheral skeletal muscular utilization of glucose, contributes to hyperglycemia at this stage.

Post-burn hepatic insulin resistance is associated with endoplasmic reticulum (ER) stress

Insulin resistance with its associated hyperglycemias represents one significant contributor to mortality in burned patients. A variety of cellular stress-signaling pathways are activated as a consequence of burn. A key player in the cellular stress response is the endoplasmic reticulum (ER). Here, we investigated a possible role for ER-stress pathways in the progression of insulin function dysregulation postburn. Rats received a 60% total body surface area thermal injury, and a laparotomy was performed at 24, 72, and 192 h postburn. Liver was harvested before and 1 min after insulin injection (1 IU/kg) into the portal vein, and expression patterns of various proteins known to be involved in insulin and ER-stress signaling were determined by Western blotting. mRNA expression of glucose-6-phosphatase and glucokinase were determined by reverse-transcriptase-polymerase chain reaction and fasting serum glucose and insulin levels by standard enzymatic and enzyme-linked immunosorbent assay techniques, respectively. Insulin resistance indicated by increased glucose and insulin levels occurred starting 24 h postburn. Burn injury resulted in activation of ER stress pathways, reflected by significantly increased accumulation of phospho-PKR-like ER-kinase and phosphorylated inositol requiring enzyme 1, leading to an elevation of phospho-c-Jun N-terminal kinase and serine phosphorylation of insulin receptor substrate (IRS) 1 postburn. Insulin administration caused a significant increase in tyrosine phosphorylation of IRS-1, leading to activation of the phosphatidylinositol 3 kinase/Akt pathway in normal liver. Postburn tyrosine phosphorylation of IRS-1 was significantly impaired, associated with an inactivation of signaling molecules acting downstream of IRS-1, leading to significantly elevated transcription of glucose-6-phosphatase and significantly decreased mRNA expression of glucokinase. Activation of ER-stress signaling cascades may explain metabolic abnormalities involving insulin action after burn.

Stress hyperglycemia in pediatric critical illness: the intensive care unit adds to the stress!

Stress hyperglycemia (SH) commonly occurs during critical illness in children. The historical view that SH is beneficial has been questioned in light of evidence that demonstrates the association of SH with worse outcomes. In addition to intrinsic changes in glucose metabolism and development of insulin resistance, specific intensive care unit (ICU) practices may influence the development of SH during critical illness. Mechanical ventilation, vasoactive infusions, renal replacement therapies, cardiopulmonary bypass and extracorporeal life support, therapeutic hypothermia, prolonged immobility, nutrition support practices, and the use of medications are all known to mediate development of SH in critical illness. Tight glucose control (TGC) to manage SH has emerged as a promising therapy to improve outcomes in critically ill adults, but results have been inconclusive. Large variations in ICU practices across studies likely resulted in inconsistent results. Future studies of TGC need to take into account the impact of commonly used ICU practices and, ideally, standardize protocols in an attempt to improve the accuracy of conclusions from such studies.

Biochemical evidence on the potential role of organophosphates in hepatic glucose metabolism toward insulin resistance through inflammatory signaling and free radical pathways

Several studies show that organophosphate pesticides exert several effects on glucose homeostasis. The current study investigates the influence of subchronic exposure to malathion (MT) on hepatic gluconeogenesis in relation to acetyl cholinesterase (AChE) inhibition, oxidative stress and inflammatory response in the rat. MT was administered by gavage at doses of 25, 50 and 100 mg/kg for 32 days. Fasting hyperglycemia was seen in line with an increased activity of hepatic phosphoenolpyruvate carboxykinase, glucose 6-phosphatase and tumor necrosis factor α. In addition to the impaired glucose tolerance and inhibition of AChE in a dose-dependent manner, there were significant increases in hepatic lipid peroxidation, carbonyl groups and 8-deoxyguanosine as the biomarkers of reactive oxygen species–mediated damage to lipid, protein and DNA, respectively. Altered quality of the liver in glucose production especially gluconeogenesis could be a compensatory mechanism against MT toxicity or even result in tissue damage. MT-induced insulin resistance in the liver occurs through oxidative and inflammatory signaling pathways.

What, how, and how much should patients with burns be fed?

The hypermetabolic response to severe burn injury is characterized by hyperdynamic circulation and profound metabolic, physiologic, catabolic, and immune system derangements. Failure to satisfy overwhelming energy and protein requirements after, and during, severe burn injury results in multiorgan dysfunction, increased susceptibility to infection, and death. Attenuation of the hypermetabolic response by various pharmacologic modalities is emerging as an essential component of the management of patients with severe burn injury. This review focuses on the more recent advances in therapeutic strategies to attenuate the hypermetabolic response and its postburn-associated insulin resistance.

Glucose control in the intensive care unit: a nutrition support perspective

Hyperglycemia commonly occurs in acutely ill patients who receive nutrition support, even in patients without a history of diabetes. The traditional view that stress hyperglycemia may be a beneficial adaptive response has been replaced by data linking hyperglycemia with increased morbidity and mortality in critically ill populations. Initial randomized studies to control stress hyperglycemia with intensive insulin infusion reported dramatic decreases in infectious complications and decreased mortality. However, recent large multicenter trials have reported that intensive insulin therapy designed to normalize blood glucose resulted in an unacceptable increase in the incidence of hypoglycemia. Review of the methods, protocols, and nutrition provided during these randomized studies is crucial to understanding the different conclusions reached and how these results may be used to influence protocols in intensive care units today. Evidence is reviewed and practical considerations are provided for nutrition support regimens to minimize stress hypoglycemia and assist glucose management.

An amino acid mixture enhances insulin-stimulated glucose uptake in isolated rat epitrochlearis muscle

Protein and certain amino acids (AA) have been found to lower blood glucose. Although these glucose-lowering AA are important modulators of skeletal muscle metabolism, their impact on muscle glucose uptake remains unclear. We therefore examined how an AA mixture consisting of 2 mM isoleucine, 0.012 mM cysteine, 0.006 mM methionine, 0.0016 mM valine, and 0.014 mM leucine impacts skeletal muscle glucose uptake in the absence or presence of a submaximal (sINS) or maximal insulin (mINS) concentration. The AA mixture, sINS, and mINS significantly increased 2-[(3)H]deoxyglucose (2-DG) uptake by 63, 79, and 298% above basal, respectively. When the AA mixture was combined with sINS and mINS, 2-DG uptake was further increased significantly by 26% (P = 0.028) and 14% (P = 0.032), respectively. Western blotting analysis revealed that the AA mixture increased basal and sINS Akt substrate of 160 kDa (AS160) phosphorylation, while AA mixture did not change phosphorylation of Akt or mammalian target of rapamycin (mTOR) under these conditions. Interestingly, addition of the AA mixture to mINS increased phosphorylation of mTOR, Akt as well as AS160, compared with mINS alone. These data suggest that certain AA increase glucose uptake in the absence of insulin and augment insulin-stimulated glucose uptake in an additive manner. Furthermore, these effects appear to be mediated via a pathway that is independent from the canonical insulin cascade and therefore may prove effective as an alternative therapeutic treatment for insulin resistance.

Toxic influence of organophosphate, carbamate, and organochlorine pesticides on cellular metabolism of lipids, proteins, and carbohydrates: a systematic review

Pesticides, including organophosphate (OP), organochlorine (OC), and carbamate (CB) compounds, are widely used in agricultural and indoor purposes. OP and CB act as acetyl cholinesterase (AChE) inhibitors that affect lots of organs such as peripheral and central nervous systems, muscles, liver, pancreas, and brain, whereas OC are neurotoxic involved in alteration of ion channels. There are several reports about metabolic disorders, hyperglycemia, and also oxidative stress in acute and chronic exposures to pesticides that are linked with diabetes and other metabolic disorders. In this respect, there are several in vitro and in vivo but few clinical studies about mechanism underlying these effects. Bibliographic databases were searched for the years 1963-2010 and resulted in 1652 articles. After elimination of duplicates or irrelevant papers, 204 papers were included and reviewed. Results indicated that OP and CB impair the enzymatic pathways involved in metabolism of carbohydrates, fats and protein within cytoplasm, mitochondria, and proxisomes. It is believed that OP and CB show this effect through inhibition of AChE or affecting target organs directly. OC mostly affect lipid metabolism in the adipose tissues and change glucose pathway in other cells. As a shared mechanism, all OP, CB and OC induce cellular oxidative stress via affecting mitochondrial function and therefore disrupt neuronal and hormonal status of the body. Establishing proper epidemiological studies to explore exact relationships between exposure levels to these pesticides and rate of resulted metabolic disorders in human will be helpful.

Hyperglycemia in aneurysmal subarachnoid hemorrhage: a potentially modifiable risk factor for poor outcome

Hyperglycemia after aneurysmal subarachnoid hemorrhage (aSAH) occurs frequently and is associated with delayed cerebral ischemia (DCI) and poor clinical outcome. In this review, we highlight the mechanisms that cause hyperglycemia after aSAH, and we discuss how hyperglycemia may contribute to poor clinical outcome in these patients. As hyperglycemia is potentially modifiable with intensive insulin therapy (IIT), we systematically reviewed the literature on IIT in aSAH patients. In these patients, IIT seems to be difficult to achieve in terms of lowering blood glucose levels substantially without an increased risk of (serious) hypoglycemia. Therefore, before initiating a large-scale randomized trial to investigate the clinical benefit of IIT, phase II studies, possibly with the help of cerebral blood glucose monitoring by microdialysis, will first have to improve this therapy in terms of both safety and adequacy.

Hyperglycemia in acute ischemic stroke: pathophysiology and clinical management

Patients with acute ischemic stroke frequently test positive for hyperglycemia, which is associated with a poor clinical outcome. This association between poor glycemic control and an unfavorable prognosis is particularly evident in patients with persistent hyperglycemia, patients without a known history of diabetes mellitus, and patients with cortical infarction. To date, however, only one large clinical trial has specifically investigated the effect of glycemic control on stroke outcome. This trial failed to show a clinical benefit, but had several limitations. Despite a lack of clinical evidence supporting the use of glycemic control in the treatment of patients with stroke, international guidelines recommend treating this subset of critically ill patients for hyperglycemia in the hospital setting. This treatment regime is, however, particularly challenging in patients with stroke, and is associated with an increased risk of the patient developing hypoglycemia. Here we review the available evidence linking hyperglycemia to a poor clinical outcome in patients with ischemic stroke. We highlight the pathophysiological mechanisms that might underlie the deleterious effects of hyperglycemia on acute stroke prognosis and systematically review the literature concerning tight glycemic control after stroke. Finally, we provide directions on the use of insulin treatment strategies to control hyperglycemia in this patient group.

Abnormal insulin sensitivity persists up to three years in pediatric patients post-burn

CONTEXT

The acute hypermetabolic response post-burn is associated with insulin resistance and hyperglycemia, significantly contributing to adverse outcome of these patients.

OBJECTIVE

The aim of the study was to examine the persistence of abnormalities of various clinical parameters commonly utilized to assess the degree of insulin resistance in severely burned children for up to 3 yr after the burn injury.

DESIGN, SETTING AND PATIENTS

A total of 194 severely burned pediatric patients, admitted to our institute between 2002 and 2007, were enrolled in this prospective study and compared to a cohort of 95 nonburned, noninjured children.

MAIN OUTCOME MEASURES

Urinary cortisol, epinephrine, and norepinephrine, serum cytokines, and resting energy requirements were determined at admission and 1, 2, 6, 9, 12, 18, 24, and 36 months post-burn. A 75-g oral glucose tolerance test was performed at similar time points; serum glucose, insulin, and C-peptide were measured; and insulin sensitivity indices, such as ISI Matsuda, homeostasis model assessment, quantitative insulin sensitivity check index, and ISI Cederholm, were calculated. Statistical analysis was performed by ANOVA with Bonferroni correction with significance accepted at P < 0.05.

RESULTS

Urinary cortisol and catecholamines, serum IL-7, IL-10, IL-12, macrophage inflammatory protein-1b, monocyte chemoattractant protein-1, and resting energy requirements were significantly increased for up to 36 months post-burn (P < 0.05). Glucose values were significantly augmented for 6 months post-burn (P < 0.05), associated with significant increases in serum C-peptide and insulin that remained significantly increased for 36 months compared to nonburned children (P < 0.05). Insulin sensitivity indices, ISI Matsuda, ISI quantitative insulin sensitivity check index, and homeostasis model assessment were abnormal throughout the whole study period, indicating peripheral and whole body insulin resistance. The insulinogenic index displayed physiological values, indicating normal pancreatic beta-cell function.

CONCLUSIONS

A severe burn is associated with stress-induced insulin resistance that persists not only during the acute phase but also for up to 3 yr post-burn.

The hepatic response to thermal injury: is the liver important for postburn outcomes?

Thermal injury produces a profound hypermetabolic and hypercatabolic stress response characterized by increased endogenous glucose production via gluconeogenesis and glycogenolysis, lipolysis, and proteolysis. The liver is the central body organ involved in these metabolic responses. It is suggested that the liver, with its metabolic, inflammatory, immune, and acute phase functions, plays a pivotal role in patient survival and recovery by modulating multiple pathways following thermal injury. Studies have evaluated the role and function of the liver during the postburn response and showed that liver integrity and function are essential for survival, and that hepatic acute phase proteins are strong predictors for postburn survival. This review discusses these studies and delineates the pivotal role of the liver in patients following severe thermal injury.

Insulin resistance postburn: underlying mechanisms and current therapeutic strategies

The profound hypermetabolic response to burn injury is associated with insulin resistance and hyperglycemia, significantly contributing to the incidence of morbidity and mortality in this patient population. These responses are present in all trauma, surgical, or critically ill patients, but the severity, length, and magnitude is unique for burn patients. Although advances in therapeutic strategies to attenuate the postburn hypermetabolic response have significantly improved the clinical outcome of these patients during the past years, therapeutic approaches to overcome stress-induced hyperglycemia have remained challenging. Intensive insulin therapy has been shown to significantly reduce morbidity and mortality in critically ill patients. High incidence of hypoglycemic events and difficult blood glucose titrations have led to investigation of alternative strategies, including the use of metformin, a biguanide, or fenofibrate, a peroxisome proliferator-activated receptor (PPAR)-gamma agonist. Nevertheless, weaknesses and potential side affects of these drugs reinforces the need for better understanding of the molecular mechanisms underlying insulin resistance postburn that may lead to novel therapeutic strategies further improving the prognosis of these patients. This review aims to discuss the mechanisms underlying insulin resistance induced hyperglycemia postburn and outlines current therapeutic strategies that are being used to modulate hyperglycemia after thermal trauma.

Effects of an intravenous endotoxin challenge on glucose and insulin dynamics in horses

OBJECTIVE

To evaluate the effects of endotoxin administered IV on glucose and insulin dynamics in horses.

ANIMALS

16 healthy adult mares.

PROCEDURES

Each week of a 2-week randomized crossover study, each horse received an IV injection (duration, 30 minutes) of Escherichia coli O55:B5 lipopolysaccharide (LPS) in 60 mL of sterile saline (0.9% NaCl) solution (20 ng/kg) or sterile saline solution alone (control treatment). Frequently sampled IV glucose tolerance test procedures were performed at 24 hours before (baseline) and 24 and 48 hours after injection; glucose and insulin dynamics were assessed via minimal model analysis.

RESULTS

13 of 16 horses had a clinical response to LPS, which was characterized by mild colic and leukopenia. Before treatment, mean +/- SD insulin sensitivity was 2.9 +/- 1.9 x 10(4) L x min(1) x mU(1); this significantly decreased to 0.9 +/- 0.9 x 10(4) L x min(1) x mU(1) 24 hours after treatment (69% reduction) and was 1.5 +/- 0.9 x 10(4) L x min(1) x mU(1) 48 hours after treatment. At baseline, mean +/- SD acute insulin response to glucose was 520 +/- 196 mU x min x L(1); this significantly increased to 938 +/- 620 mU x min x L(1) (80% increase) and 755 +/- 400 mU x min x L(1) (45% increase) at 24 and 48 hours after LPS treatment, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with baseline values, insulin sensitivity was decreased for 24 hours after IV injection of LPS, and affected horses had a compensatory pancreatic response. These disturbances in glucose and insulin dynamics may contribute to development of laminitis in horses.

Adrenaline potentiates insulin-stimulated PKB activation in the rat fast-twitch epitrochlearis muscle without affecting IRS-1-associated PI 3-kinase activity

We have previously shown in the rat slow-twitch soleus muscle that adrenaline greatly potentiates insulin-stimulated protein kinase B (PKB) phosphorylation without having an effect alone. However, insulin signalling capacity through the PKB pathway is higher in soleus than in fast-twitch muscles, whereas adrenaline activates phosphorylase more strongly in epitrochlearis. Therefore, the aim of the present study was to investigate the interaction between adrenaline and insulin signalling in the fast-twitch epitrochlearis muscle. Insulin increased insulin receptor substrate-1 (IRS-1)-associated phosphoinositide (PI) 3-kinase activity threefold, and adrenaline did not influence basal or insulin-stimulated PI 3-kinase activity. Insulin but not adrenaline increased PKB activity and phosphorylation of Ser(473) and Thr(308). It is interesting to note that adrenaline potentiated insulin-stimulated PKB activity and PKB Ser(473) and Thr(308) phosphorylation. These effects were mimicked by dibutyryl-cyclic adenosine monophosphate (db-cAMP). Adrenaline and db-cAMP increased glycogen synthase kinase (GSK)-3beta Ser(9) phosphorylation independently of PKB activation and enhanced insulin-stimulated GSK-3beta Ser(9) phosphorylation. Although adrenaline increased GSK-3 phosphorylation (inhibiting activity), phosphorylation of its target sites on glycogen synthase was increased, and adrenaline blocked insulin-stimulated glycogen synthase dephosphorylation of Ser(641) and Ser(645,649,653,657), glycogen synthase activation and glycogen synthesis. Insulin-stimulated glucose transport was not influenced by adrenaline despite the increased PKB activation. In conclusion, as in the slow-twitch soleus muscle, adrenaline potentiates insulin-stimulated PKB activation in the fast-twitch glycolytic epitrochlearis muscle without increasing IRS-1-associated PI 3-kinase activity. Furthermore, adrenaline induces phosphorylation of a pool of GSK-3 that is not involved in the regulation of glycogen metabolism. These results indicate that the combination of adrenaline and insulin may activate novel signalling molecules rather than just summing up their effects on linear pathways.

Hemodynamic and metabolic effects of selective beta1 adrenergic blockade during sepsis

BACKGROUND

Selective beta adrenergic antagonists are commonly used to reduce myocardial demise in patients at risk for cardiac-related death. The purpose of this study was to examine the hemodynamic and metabolic effects of cardiac selective beta adrenergic blockade in patients.

METHODS

Muscle protein kinetics were quantified using isotopic tracer methodology in 6 moderately septic, mechanically ventilated patients with pneumonia before and then at the conclusion of a 3-hour infusion of esmolol of sufficient dose to reduce heart rate by 20% from baseline. A battery of hemodynamic measurements as facilitated by a thermodilution pulmonary artery catheter and indirect calorimetry were also measured before and after the 3-hour selective beta adrenergic blockade.

RESULTS

Selective beta adrenergic blockade was associated with the 20% reduction in heart rate and a comparable decrease in cardiac output. Esmolol administration failed to affect systemic or pulmonary vascular resistance, oxygen consumption, hepatic or leg blood flow, energy expenditure, or ATP availability/energy charge within muscle. Esmolol infuse did incite a shift in fuel oxidation toward an increase in palmitate oxidation and with a decrease in the oxidation of glucose. There was no demonstrable influence beta1 adrenergic blockade on muscle protein kinetics.

CONCLUSIONS

Cardiac selective beta adrenergic blockade with esmolol reduces cardiac output in proportion to the percentage decreases in heart rate in moderately severe septic patients without adversely affecting oxygen utilization or hepatic, peripheral blood flow.

Hyperglycemia in the Critically Ill Patient

Hyperglycemia and insulin resistance are common among critically ill patients and occur in patients with or without a history of diabetes mellitus. All patients undergoing critical illness are at risk for stress-induced hyperglycemia. Some patients may be at greater risk for hyperglycemia than others when considering underlying disease states and iatrogenic factors. Many recent studies demonstrate that tight glucose control can decrease morbidity and mortality associated with critical illness. This article reviews the pathophysiology behind stress-induced hyperglycemia, the evidence to support tight glycemic control, and the importance of an intensive insulin therapy protocol to standardize treatment among critical care patients.

Adrenergic receptor stimulation attenuates insulin-stimulated glucose uptake in 3T3-L1 adipocytes by inhibiting GLUT4 translocation

Activation of the sympathetic nervous system inhibits insulin-stimulated glucose uptake. However, the underlying mechanisms are incompletely understood. Therefore, we studied the effects of catecholamines on insulin-stimulated glucose uptake and insulin-stimulated translocation of GLUT4 to the plasma membrane in 3T3-L1 adipocytes. We found that epinephrine (1 microM) nearly halved insulin-stimulated 2-deoxyglucose uptake. The beta-adrenoceptor antagonist propranolol (0.3 microM) completely antagonized the inhibitory effect of epinephrine on insulin-stimulated glucose uptake, whereas the alpha-adrenoceptor antagonist phentolamine (10 microM) had no effect. When norepinephrine was used instead of epinephrine, the results were identical. None of the individual selective beta-adrenoceptor antagonists (1 microM, beta(1): metoprolol, beta(2): ICI-118551, beta(3): SR-59230A) could counteract the inhibitory effect of epinephrine. Combination of ICI-118551 and SR-59230A, as well as combination of all three selective beta-adrenoceptor antagonists, abolished the effect of epinephrine on insulin-stimulated glucose uptake. After differential centrifugation, we measured the amount of GLUT1 and GLUT4 in the plasma membrane and in intracellular vesicles by means of Western blotting. Both epinephrine and norepinephrine reduced insulin-stimulated GLUT4 translocation to the plasma membrane. These results show that beta-adrenergic (but not alpha-adrenergic) stimulation inhibits insulin-induced glucose uptake in 3T3-L1 adipocytes, most likely via the beta(2)- and beta(3)-adrenoceptor by interfering with GLUT4 translocation from intracellular vesicles to the plasma membrane.

Impaired expression and insulin-stimulated phosphorylation of Akt-2 in muscle of obese patients with atypical diabetes

Although a pharmacological dose of insulin produces a dramatic increase in phosphorylation and activity of Akt isoforms 1 and 2 in mammalian skeletal muscle, few studies have examined the effect of physiological concentrations of insulin on the phosphorylation of Akt-1 and -2 in normal and diabetic tissue. This study examined the patterns of insulin-stimulated Akt isoform phosphorylation and protein expression in muscle biopsies obtained from obese patients with atypical diabetes immediately after a hyperglycemic crisis and again after near-normoglycemic remission. In obese patients with new-onset diabetes mellitus presenting with hyperglycemic crisis (plasma glucose 30.5 +/- 4.8 mM), in vitro stimulation of vastus lateralis muscle biopsies with 100 microU/ml (0.6 nM) insulin increased insulin receptor phosphorylation threefold and Akt-1 phosphorylation on Ser(473) twofold, whereas Akt-2 phosphorylation was not stimulated. After 10-wk intensive insulin therapy that led to near-normoglycemic remission and discontinuation of insulin therapy, both Akt-2 expression and insulin-stimulated Akt-2 Ser(474) phosphorylation doubled. Hyperglycemic crisis did not affect insulin-stimulated threonine phosphorylation of either Akt-1 or Akt-2. The decreased Akt-2 expression at presentation was accompanied by reduced GLUT4 protein expression and increased expression of enzymes counterregulatory to insulin action. Thus a physiological concentration of insulin stimulated Akt-1 and Akt-2 phosphorylation in human skeletal muscle in the absence of hyperglycemia, but Akt-2 expression and stimulation appeared to be impaired in muscle of obese patients with atypical diabetes presenting with severe hyperglycemia.

Insulin resistance and hyperglycemia in critical illness: role of insulin in glycemic control

Alterations in glucose metabolism, including hyperglycemia associated with insulin resistance, occur in critical illness. Acutely, such alterations result from normal, adaptive activation of endocrine responses, including increased release of catecholamines, cortisol, and glucagon and a reduced glucose uptake capacity. In prolonged critical illness, neuroendocrine changes lead to more extensive metabolic changes that may be associated with development of complications and poor prognosis. Until recently, hyperglycemia was not routinely controlled in intensive care units, except among patients with known diabetes mellitus. Studies have demonstrated that glycemic management in postmyocardial infarction in patients with diabetes is an effective practice. Recent investigation has extended this to demonstrate reduced morbidity and mortality in a surgical critically ill population with and without diabetes mellitus in later phases of critical illness. Although the mechanisms for improved patient outcomes need to be established, this novel approach to management of hyperglycemia in critical illness is a new and important concept for those working in critical care. This article reviews alterations in glucose metabolism which occur in critically ill patients and discusses potential mechanisms and mediators (e.g., hormones, cytokines) that may play a key role in hyperglycemia and insulin resistance during acute and prolonged phases of severe illness. The article addresses the application of insulin protocols and exogenous regulation of glucose concentration in critical illness based on a review of recent intervention studies.