Conditions Of Insulin Deficiency Research Articles

Contrast-Free FLIM Reveals Metabolic Changes in Pathological Islets of Langerhans.

FLIM (Fluorescence Lifetime Imaging Microscopy) is a powerful tool that could be used in the future to diagnose islet cell recovery after therapy. The identification of appropriate FLIM parameters is required to determine islet quality and islet cell metabolism throughout the organ under various conditions of insulin deficiency. The aim of the work was to identify key FLIM parameters, changes of which are characteristic of pancreatic pathologies. The τm, τ1, τ2, α1, α2 and α1/α2 of free and bound forms of NAD(P)H of the islet cells of animals (rats and pigs) and of humans with and without pathologies were measured and analyzed. The data were confirmed by IHC and histological studies. We identified three FLIM parameters in islet cells from animals with streptozotocin (STZ)-induced diabetes mellitus (DM) and from humans with chronic pancreatitis + type 2 diabetes (T2D), which differ in the same way: τm and α2 take lower values compared to the nonpathological islet cells, while α1/α2 takes higher values. In islet cells from patients with adenocarcinoma (PDAC) and chronic pancreatitis, these parameters had reverse tendency relative to the norm or did not differ. Thus, minimally invasive and non-contrast FLIM methods may, in the future, be used to diagnose pathological islet cells.

The hepatoprotective effects of n3-polyunsaturated fatty acids against non-alcoholic fatty liver disease in diabetic rats through the FOXO1/PPARα/GABARAPL1 signalling pathway

AimWe compared the efficacy of n3-polyunsaturated fatty acids (n3-PUFAs) and metformin in halting the progression of non-alcoholic fatty liver disease (NAFLD) developed in the milieu of insulin deficiency. Main methodsNAFLD was induced by a chronic high-fat diet (HFD) in male Sprague Dawley rats, rendered diabetic by a low dose streptozotocin (STZ). Diabetic rats were treated with n3-PUFAs (300 mg/kg/d) or metformin (150 mg/kg/d) for 8 weeks. Improvements in the NAFLD score and hepatic insulin resistance (IR) were addressed and correlated to changes in the hepatic expression of Forkhead box protein O1 (FOXO-1), microtubule-associated proteins 1A/1B light chain 3B (MAP1LC3B) and gamma-aminobutyric acid receptor-associated protein-like 1 (GABARAPL1) genes. Hepatic peroxisome proliferator-activated receptor alpha (PPAR-α), and B-cell lymphoma 2 (Bcl-2) protein expression was also assessed. Key findingsDriven by insulin deficiency and HFD, the FOXO-1 gene along with its downstream targets, MAP1LC3B and GABARAPL1, were highly expressed in the liver tissue of the HFD/STZ group. Meanwhile, hepatic expression of PPAR-α and Bcl-2 was markedly decreased. These abnormalities coincided with a marked increase in the hepatic IR and NAFLD activity. Comparable to metformin, n3-PUFAs were able to rearrange hepatic PPAR-α and FOXO-1 expression in HFD/STZ rats, resulting in improved diabetic/steatotic liver phenotype. SignificanceAlong with the enhancement of PPAR-α expression, inhibition of FoxO1/GABARAPL1/MAP1LC3B transcription is suggested as a core mechanism for the protective effects of n3-PUFAs on hepatic IR and NAFLD. Under conditions of insulin deficiency, n3-PUFAs retain their potential as a safe and promising approach for the control of NAFLD.

Medical errors in providing emergency care to patients with ECG symptoms of acute coronary syndrome on the background of decompensation of diabetes mellitus with hyperkalemia

The article describes a rare clinical case of hyperkalemia backgrounded by type 1 diabetes mellitus with signs of acute cardiovascular insufficiency, arrhythmia and QRST disturbances which was primarily diagnosed as acute coronary syndrome with ST elevation. Coronary angiography excluded pathology of the coronary arteries. Hyperkalemia, as the cause of ECG changes, was suspected in the hospital treatment. Stabilization of the patient’s condition, renewal of heart rhythm and conduction was obtained against the background of infusion support and insulin therapy. The pathogenesis of arrhythmia and QRST complex had a secondary genesis in relation to fluid and electrolyte metabolism disorders, so the restoration of sinus rhythm occurred without usage of antiarrhythmics. The usage of antiarrhythmic drugs according to the guideline of management of patients with ACS can deepen electrolyte shifts and lead to fatal arrhythmias in conditions of insulin deficiency and hyperkalemia. This example illustrates the urgent need to diagnose life-threatening electrolyte changes, namely hyperkalemia, under the guise of acute coronary syndrome, as well as signs of ACS, along with ECG, to pay special attention to the assessment of medical history and clinical data for the correct choice of emergency care and further treatment tactics.

Influence of lipoic acid on the exchange of sialic acids in small intestine of rats with alloxan diabetes

Despite comprehensive study of features of the reasons and a pathogeny of a diabetes mellitus, its timely diagnostics, prevention and treatment remain among the most current problems of medicine. The patients suffering from the diabetes mellitus a long time have various forms of pathology of a digestive tract forming a picture of a gastroenterological form of autonomous neuropathy. At a diabetic polyneuropathy widely use drugs of -lipoic acid of acid which is the universal antioxidant functioning as a cofactor in the multifermental complexes catalyzing oxidizing decarboxylation of -keto acids, and therefore playing an important role in the course of obtaining energy in aerobic conditions taking part in regeneration of other antioxidants. Sialic acids which belong to multifunctional connections, being components various the glycoproteins and glycolipids of connections are a part of mucins of a blanket of a wall of a small bowel. The composition of mucins of the protective layer of the wall of the small intestine includes sialic acids, which are multifunctional compounds that are components of glycoproteins and glycolipids. The purpose of this study was a comparative study of the effect of lipoic acid on the indicators of sialic acid metabolism of rat small intestine wall compounds in alloxan diabetes. An increase in the rate of sialic acid metabolism in the wall of the small intestine of rats with alloxan diabetes was found, which may indicate a restructuring of the metabolism of enterocytes to adapt to conditions of insulin deficiency and hyperglycemia. The introduction of lipoic acid to experimental animals did not reduce sialidase activity and the content of all fractions of sialic acids in the wall of the small intestine, although, according to the literature, it reduced the degree of development of oxidative stress in the body, including in the studied section of the gastrointestinal tract.

Biochemical and cellular properties of insulin receptor signalling.

The mechanism of insulin action is a central theme in biology and medicine. In addition to the rather rare condition of insulin deficiency caused by autoimmune destruction of pancreatic β-cells, genetic and acquired abnormalities of insulin action underlie the far more common conditions of type 2 diabetes, obesity and insulin resistance. The latter predisposes to diseases ranging from hypertension to Alzheimer disease and cancer. Hence, understanding the biochemical and cellular properties of insulin receptor signalling is arguably a priority in biomedical research. In the past decade, major progress has led to the delineation of mechanisms of glucose transport, lipid synthesis, storage and mobilization. In addition to direct effects of insulin on signalling kinases and metabolic enzymes, the discovery of mechanisms of insulin-regulated gene transcription has led to a reassessment of the general principles of insulin action. These advances will accelerate the discovery of new treatment modalities for diabetes.

Abstract 192: Intra-Individual Temporal Variation of Lipid and Apolipoprotein Levels in Patients With Type II Diabetes Mellitus and Normolipidemic Individuals

Hypertriglyceridemia is frequently observed with diabetes mellitus (DM) and is associated with increased cardiovascular disease (CVD) risk. In conditions of insulin deficiency or resistance, increased levels of free fatty acids are seen by the liver, which trigger increased lipogenesis and secretion of triglyceride (TG) rich lipoprotein (TRL) particles. However, a high number of specific ApoC-III on TRL particles suppress their return to the liver leading to a continuous circulation of highly atherogenic TRL remnants. To better understand the effect of intra-individual temporal variations on the differentiation of lipid and apolipoprotein profiles in DM vs. normal individuals, a small time course study over a 4 week period was performed on 3 normolipidemic, and 3 type II DM patients. Our laboratory has developed a method to separate lipoproteins based on hydrodynamic size coupled with mass spectrometry based analysis. Whole serum and lipoprotein size fractions were analyzed for 8 apolipoproteins (ApoA-I, ApoA-II, ApoA-IV, B-100, ApoC-I, ApoC-II, ApoC-III and E) and non-polar lipids (FC, CE, TG) while monitoring other proteins (ApoD, ApoM, CETP, LCAT, PLTP, PON1 and SAA4). In whole serum over the course of 4 weeks, ApoA-IV levels of DM vs. normal subjects differed the most, 3.2 (0.7) vs. 1.8 (0.4) μM, respectively, more significantly than intra-group or intra-individual variations. On the contrary, significantly lower whole serum levels were found for FC, CE, ApoM and PON1 (Prob<0.01). HDL-ApoC-III/LDL-ApoC-III was also lower in DM vs. normal subjects, 3.0 (1.9) vs. 7.2 (4.1). By metrics of molar ratio measured in 20-35 nm LDL fractions, the most significant difference was found between DM vs. normal subjects in ApoC-III/ApoB-100 (1.8 (0.6) vs. 0.9 (0.3)), C-II/ApoB-100 (0.8 (0.4) vs. 0.4 (0.2)) and ApoE/ApoC-III (0.11 (0.09) vs. 0.24 (0.15)). These LDL composition differences indicate lower lipase activity and inhibition of LDL uptake. However, no significant differences were observed in these molar ratios as function of LDL particle size. In conclusion, due to less significant temporal deviations, apolipoprotein molar ratios are a more useful and informative measure of CVD risk in DM subjects than LDL size distribution characteristics.

An Indirect Action Contributes to C-Fos Induction in Paraventricular Hypothalamic Nucleus by Neuropeptide Y.

Neuropeptide Y (NPY) is a well-established orexigenic peptide and hypothalamic paraventricular nucleus (PVH) is one major brain site that mediates the orexigenic action of NPY. NPY induces abundant expression of C-Fos, an indicator for neuronal activation, in the PVH, which has been used extensively to examine the underlying NPY orexigenic neural pathways. However, PVH C-Fos induction is in discordance with the abundant expression of NPY receptors, a group of inhibitory Gi protein coupled receptors in the PVH, and with the overall role of PVH neurons in feeding inhibition, suggesting a mechanism of indirect action. Here we showed that the ability of NPY on C-Fos induction in the PVH was blunted in conditions of insulin deficiency and fasting, a condition associated with a high level of NPY and a low level of insulin. Moreover, insulin insufficiency blunted C-Fos induction in the PVH by fasting-induced re-feeding, and insulin and NPY induced c-Fos induction in the same group of PVH neurons. Finally, NPY produced normal C-Fos induction in the PVH with disruption of GABA-A receptors. Thus, our results revealed that PVH C-Fos induction by NPY is mediated by an indirect action, which is at least partially mediated by insulin action, but not GABA-A receptors.

Possible contribution of taurine to distorted glucagon secretion in intra-islet insulin deficiency: a metabolome analysis using a novel α-cell model of insulin-deficient diabetes.

Glycemic instability is a serious problem in patients with insulin-deficient diabetes, and it may be due in part to abnormal endogenous glucagon secretion. However, the intracellular metabolic mechanism(s) involved in the aberrant glucagon response under the condition of insulin deficiency has not yet been elucidated. To investigate the metabolic traits that underlie the distortion of glucagon secretion under insulin deficient conditions, we generated an αTC1-6 cell line with stable knockdown of the insulin receptor (IRKD), i.e., an in vitro α-cell model for insulin-deficient diabetes, which exhibits an abnormal glucagon response to glucose. A comprehensive metabolomic analysis of the IRKD αTC1-6 cells (IRKD cells) revealed some candidate metabolites whose levels differed markedly compared to those in control αTC1-6 cells, but also which could affect the glucagon release in IRKD cells. Of these candidates, taurine was remarkably increased in the IRKD cells and was identified as a stimulator of glucagon in αTC1-6 cells. Taurine also paradoxically exaggerated the glucagon secretion at a high glucose concentration in IRKD cells and islets with IRKD. These results indicate that the metabolic alterations induced by IRKD in α-cells, especially the increase of taurine, may lead to the distorted glucagon response in IRKD cells, suggesting the importance of taurine in the paradoxical glucagon response and the resultant glucose instability in insulin-deficient diabetes.

Saturated fatty acids activate ERK signaling to downregulate hepatic sortilin 1 in obese and diabetic mice

Hepatic VLDL overproduction is a characteristic feature of diabetes and an important contributor to diabetic dyslipidemia. Hepatic sortilin 1 (Sort1), a cellular trafficking receptor, is a novel regulator of plasma lipid metabolism and reduces plasma cholesterol and triglycerides by inhibiting hepatic apolipoprotein B production. Elevated circulating free fatty acids play key roles in hepatic VLDL overproduction and the development of dyslipidemia. This study investigated the regulation of hepatic Sort1 in obesity and diabetes and the potential implications in diabetic dyslipidemia. Results showed that hepatic Sort1 protein was markedly decreased in mouse models of type I and type II diabetes and in human individuals with obesity and liver steatosis, whereas increasing hepatic Sort1 expression reduced plasma cholesterol and triglycerides in mice. Mechanistic studies showed that the saturated fatty acid palmitate activated extracellular signal-regulated kinase (ERK) and inhibited Sort1 protein by mechanisms involving Sort1 protein ubiquitination and degradation. Consistently, hepatic ERK signaling was activated in diabetic mice, whereas blocking ERK signaling by an ERK inhibitor increased hepatic Sort1 protein in mice. These results suggest that increased saturated fatty acids downregulate liver Sort1 protein, which may contribute to the development of dyslipidemia in obesity and diabetes.

Chronic Treatment with the AMP-Kinase Activator AICAR Increases Glycogen Storage and Fatty Acid Oxidation in Skeletal Muscles but Does Not Reduce Hyperglucagonemia and Hyperglycemia in Insulin Deficient Rats

This study tested whether the glycogen-accumulating effect of chronic in vivo pharmacological 5′AMP-activated protein kinase (AMPK) activation could improve glycemic control under conditions of insulin deficiency. Male Wistar rats were rendered diabetic through the administration of streptozotocin (STZ) and then treated for 7 consecutive days with the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR). Subsequently, glycogen content and synthesis, glucose oxidation, and fatty acid oxidation (FAO) were determined in oxidative and glycolytic skeletal muscles. Glycemia, insulinemia, glucagonemia, and circulating triglycerides (TG) and non-esterified fatty acids (NEFAs) were measured after AICAR treatment. Insulin was almost undetectable in STZ rats and these animals were severely hyperglycemic. Glycogen content was markedly low mainly in glycolytic muscles of STZ rats and AICAR treatment restored it to control values. No differences were found among all muscles studied with regards to the content and phosphorylation of Akt/protein kinase B and glycogen synthase kinase 3. Even though glycogen synthase content was reduced in all muscles from STZ rats, insulin-induced dephosphorylation/activation of this enzyme was preserved and unaffected by AICAR treatment. Glucagon and NEFAS were 2- and 7.4-fold fold higher in STZ rats than controls, respectively. AICAR did not affect hyperglycemia and hyperglucagonemia in STZ rats; however, it normalized circulating NEFAs and significantly increased FAO in glycolytic muscles. In conclusion, even though AICAR-induced AMPK activation enhanced glycogen accumulation in glycolytic muscles and normalized circulating NEFAs and TG levels, the hyperglycemic effects of glucagon likely offset the potentially glucose-lowering effects of AICAR, resulting in no improvement of glycemic control in insulin-deficient rats.

Changes in the Fatty Acid Composition under Conditions of Polyneuropathy Related to Type 1 Diabetes Mellitus

We analyzed the composition of fatty acids in blood plasma of teenagers suffering from polyneuropathy and microangiopathy developed against the background of type 1 diabetes mellitus. It was found that the normalized contents of oleic (monounsaturated) and palmitic (saturated) fatty acids increase in this case, while the levels of stearic (saturated) and linoleic (polyunsaturated) acids decrease, as compared to the norm. These shifts can be related to intensification of release of lipids from adipose tissues and result in disorders of the metabolic processes in nerve cells (first of all, in their membranes). Changes in the balance of fatty acids in erythrocytes of the examined patients appeared as a decrease in the level of saturated stearic acid and increases in the levels of saturated palmitic and polyunsaturated linoleic acids. A relative decrease in the sum of levels of dihomo-γ-linolenic and docosahexaenoic polyunsaturated fatty acids was also found. The observed changes in the composition of the cell membranes (those of erythrocytes) can be indicative of the existence of systemic cellular membranopathy under conditions of the above-mentioned pathologies. Decreased activities of Δ6- and Δ5-desaturases under conditions of insulin deficiency can be one of the reasons for these disorders.

Determinants of undercarboxylated and carboxylated osteocalcin concentrations in type 1 diabetes

To determine whether undercarboxylated osteocalcin (UC-OC) or gamma-carboxyglutamic-carboxylated-type osteocalcin (GLA-OC) concentrations deviate from normal in type 1 diabetes (T1D), serum levels were compared between 115 subjects with T1D and 55 age-matched healthy controls. UC-OC and GLA-OC concentrations were similar between groups; however, in T1D, UC-OC correlated positively with markers of insulin exposure, either endogenously produced or exogenously administered. A study was conducted to determine whether dysregulation of circulating concentrations of UC-OC or GLA-OC occurs in patients with type 1 diabetes, a condition of insulin deficiency without insulin resistance. We measured serum concentrations of UC-OC and GLA-OC in 115 subjects with T1D, ages 14-40 years, and in 55 age-matched healthy control subjects. Relationships between UC-OC and GLA-OC concentrations and patient characteristics (gender and age), indices of glycemic control (hemoglobin A1c (HbA1c), fasting plasma glucose, C-peptide concentration, 3-day average glucose measured by a continuous glucose sensor, total daily insulin dose) and circulating indices of skeletal homeostasis (total calcium, 25-OH vitamin D, parathyroid hormone, insulin-like growth factor 1 (IGF-1), type 1 collagen degradation fragments (CTX), adiponectin, leptin) were examined. Between group differences in the concentrations of UC-OC and GLA-OC were the main outcome measures. Although adiponectin levels were higher in the T1D group, between-group comparisons did not reveal statistically significant differences in concentration of UC-OC, GLA-OC, CTX or leptin between the T1D and control populations. Instead, by multivariate regression modeling, UC-OC was correlated with younger age (p < 0.001), higher CTX (p < 0.001), lower HbA1c (p = 0.013), and higher IGF-1 (p = 0.086). Moreover, within the T1D subgroup, UC-OC was positively correlated with C-peptide/glucose ratio (reflecting endogenous insulin secretion), with IGF-1 (reflecting intra-portal insulin sufficiency), and with total daily insulin dose. In T1D, UC-OC appears to correlate positively with markers of insulin exposure, either endogenously produced or exogenously administered.

Hypoglycemic potency of novel trivalent chromium in hyperglycemic insulin-deficient rats

Two sources of chromium III, “chromium 454” and “chromium picolinate,” were tested in insulin-deficient Streptozocin-treated diabetic rats. This model was selected in order to evaluate the possibility of any hypoglycemic potency of chromium in a relative absence of blood insulin concentration. Three weeks of the treatment with CRC454 and CrP resulted in a 38% and 11% reduction of blood glucose levels, respectively. Body weight gains were equally improved by both treatments. Blood levels of CK, ALT and AST were significantly reduced by CRC454 and CrP. These results might suggest that any hypoglycemic effect of trivalent chromium under insulin-deficient conditions could be largely dependent upon the type of chromium agent and associated characteristics such as solubility and bioavalibility. In contrast, improvement of body weight gains and blood levels of CK, AST and ALT seems to be less dependent on the type of chromium compound under these experimental conditions. In conclusion, CRC454 showed significant reduction of hyperglycemia under insulin-deficient conditions.

Type 1 diabetes leads to cytoskeleton changes that are reflected in insulin action on rat cardiac K(+) currents.

A sustained K(+) current (I(ss)) is attenuated in ventricular cells from streptozotocin (STZ)-induced diabetic rats. The in vitro addition of insulin to isolated cells augments I(ss) in a process that is blocked by disrupting either actin microfilaments (with cytochalasin D) or microtubules (with colchicine). When these agents are added at progressively later times, the effect of insulin becomes evident in a time-dependent manner. I(ss) is also augmented by insulin in control cells in a cytoskeleton-dependent manner. However, in contrast to diabetic cells, cytoskeleton-dependent augmentation of I(ss) by insulin occurs at a considerably faster rate in control cells. Immunofluorescent labeling shows a reduced density of beta-tubulin in diabetic cells, particularly in perinuclear regions. In vitro insulin replacement or in vivo insulin injections given to STZ-treated rats enhances beta-tubulin density. These results suggest an impairment of cytoskeleton function and structure under insulin-deficient conditions, which may have implications for cardiac function.

Benzo[a]pyrene- and TCDD-induced alterations in tyrosine phosphorylation and insulin-like growth factor signaling pathways in the MCF-10A human mammary epithelial cell line.

Previous studies in this laboratory have shown that polycyclic aromatic hydrocarbons, such as benzo[a]pyrene (BaP), and certain halogenated aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), modulate receptor signaling pathways in human lymphoid and non-lymphoid cells. We have recently demonstrated that BaP produces a weak mitogenic signal in human mammary epithelial cells, perhaps by mimicking growth factor signaling pathways. In the present studies we found that BaP and TCDD activated insulin-like growth factor (IGF-I) signaling pathways under insulin-deficient conditions. The effects of BaP and TCDD were evaluated in the human MCF-10A mammary epithelial cell line grown under epidermal growth factor- and insulin-dependent conditions. BaP (0.3 microM) and TCDD (30 nM) were found to restore a moderate insulin-like signal in MCF-10A cells grown in the absence of added insulin. TCDD was more potent and produced better activation of cell growth than did BaP. Both TCDD and BaP appeared to mimic signaling through the IGF-I receptor (IGF-IR), as evidenced by increased tyrosine phosphophorylation of IGF-IRbeta, IRS-1 and Shc. In addition, both BaP and TCDD significantly increased the activity of phosphatidylinositol 3-kinase (PI3K). The PI3K inhibitor LY294002 was found to inhibit the growth-promoting effects of TCDD seen under insulin-deficient conditions. The results of these studies show that under certain conditions BaP and TCDD can mimic growth factor signaling pathways in human mammary epithelial cells, demonstrating that environmentally prevalent carcinogenic compounds may alter cell growth in human mammary epithelial cells via mimicry of growth factor receptor signaling pathways.

Plasma leptin in diabetic and insulin-treated diabetic and normal rats

Adipose tissue leptin mRNA levels are decreased by food deprivation or induction of insulin-deficient diabetes. To determine whether plasma leptin concentrations are similarly affected, whether treatment of diabetes with insulin restores plasma leptin, and whether this requires restoration of body weight (lost as a result of diabetes) and/or normalization of glycemia, we measured plasma leptin concentrations in control, untreated streptozotocin (STZ)-diabetic, and insulin-treated STZ-diabetic rats. Plasma leptin was markedly reduced in untreated STZ-diabetic rats. Insulin treatment for 4 to 17 days increased plasma leptin approximately twofold above control levels. However, despite the hyperleptinemia, insulin-treated diabetic rats gained weight at a rate equal to that of sham-treated controls. Epididymal adipose tissue leptin mRNA levels in 17-day insulin-treated diabetic rats were equal to but did not exceed sham-control levels, unlike plasma leptin. Plasma glucose concentrations in insulin-treated STZ-diabetic rats were lower than in sham controls. Therefore, to determine whether hypoglycemia may be important in increasing plasma leptin, we measured plasma leptin levels in diabetic rats infused with insulin for 3 hours along with a variable-rate glucose infusion targeting glycemia to 200 or 40 mg/100 mL. Plasma leptin rapidly increased in these rats irrespective of target glycemia. Plasma leptin also increased rapidly in normal rats infused with insulin and glucose (target glycemia, 200 mg/100 mL). We conclude that plasma leptin concentrations are markedly reduced under conditions of insulin deficiency and rapidly increased by insulin treatment. The increase in plasma leptin does not require restoration of body weight and, under glucose clamp conditions, does not depend on target glycemia. Hyperleptinemia in insulin-treated diabetic rats is not explained on the basis of steady-state leptin mRNA levels, at least as reflected in epididymal fat.

Antidiabetogenic action of truncated glucagon-like peptide-1 in mice

Besides its well-known stimulatory action on insulin secretion, glucagon-like peptide-1 (7-36)amide (= GLP-1) has been shown to increase the insulin-independent glucose uptake in normal individuals and the glucose elimination rate during short term conditions in diabetes. Whether such an action is evidented also in rodents and whether it persists after long-term administration are not known. This study therefore examined the influence of the peptide on glucose elimination in insulin deficient diabetic mice both acutely and following long-term administration. GLP-1 was injected intravenously (1 or 32 nmol/kg) together with glucose (2.8 mmol/kg) in both normal and alloxan-diabetic mice. It was found that the peptide at 32 nmol/kg potentiated the glucose elimination rate in both groups, i.e. also under insulin deficient conditions. In normal animals, GLP-1 also potentiated glucose-stimulated insulin secretion. In a second experimental series, GLP-1 was injected subcutaneously at 0.33 or 1.5 nmol twice daily to normal and alloxan-diabetic mice. After 5 days of treatment by the peptide at 1.5 nmol twice daily, the glucose elimination rate was potentiated in both groups, also when the intravenous glucose tolerance test was performed 4 h after the last injection of GLP-1. We therefore conclude that the glucose elimination is enhanced by GLP-1 in both normal and alloxan-diabetic mice, and that this effect persists after a 5 day course of subcutaneous treatment.

Acute hyperinsulinemia increases neuropeptide Y concentrations in the hypothalamic arcuate nucleus of fasted rats

Neuropeptide Y, a major hypothalamic peptide, stimulates feeding, insulin secretion and weight gain when injected intrahypothalamically. Hypothalamic NPY may be regulated by insulin availability at hypothalamic level, as its activity is apparently inhibited by intrahypothalamic insulin administration and is stimulated under insulin-deficient conditions. To determine the effects of acute physiological hyperinsulinemia, we measured regional hypothalamic NPY levels in rats during a hyperinsulinemic, euglycemic clamp. Seven male Wistar rats with implanted jugular cannulae, fasted for 24 h, were infused with insulin at 100 mU/h together with variable-rate glucose to maintain euglycemia (3.9±0.1 mmmol/l), for 150 min. Controls were infused for the same period with polygeline vehicle alone (n=8), and had blood glucose concentrations of 4.0±0.5 mmol/l. Insulin levels were 80.2±3.9 mU/l in insulin-infused rats and 15.2±1.4 mU/l in polygeline-treated controls (p<0.001). NPY levels, measured by radioimmunoassay, were significantly higher in the arcuate nucleus/median eminence (ARC/ME) of hyperinsulinemic rats than in controls (4.8±1.2 vs 2.5±0.6 fmol/ μg protein; p< 0.001), but were comparable with controls in 7 other hypothalamic regions. Acute physiological hyperinsulinemia therefore increases NPY levels selectively in the ARC/ME. Insulin could cause NPY accumulation in the ARC by blocking its transport to NPY-sensitive areas. This would be consistent with the suggestions that insulin inhibits hypothalamic NPY activity and also acts as a central satiety factor.

Changes in the activity of enzymes, participating in glycogen metabolism of alloxan diabetic rats

Alloxan diabetes induced in white rats by intraperitoneal injection of alloxan-monohydrate (15 mg/100 g body weight) was used to study changes in the glycogen phosphorylase a and b, phosphoprotein phosphatases and hexokinase activities under insulin deficiency conditions. Among the enzymes studied, an increase in muscle phosphorylase a activity as well as the a/b ratio have been obtained. In diabetic muscle phosphoprotein phosphatases and hexokinase activities were diminished. AMP increased the liver glycogen phosphorylase activity twice in diabetic rats whereas in normal animals the enzyme was less sensitive to this effector. The changes in liver hexokinase activity at diabetes were not connected and correlated with the altered phosphorylase and protein phosphatase activities. The logical chain of probable molecular events taking place in muscle glycogen metabolism under the conditions of insulin deficiency is offered.

Direct evidence for a stimulatory effect of hyperglycemia per se on peripheral glucose disposal in type II diabetes.

The effect of hyperglycemia per se on glucose uptake by muscle tissue was quantitated in six controls and six type II diabetics by the forearm technique, under conditions of insulin deficiency induced by somatostatin (SRIF) infusion (0.7 mg/h). Blood glucose concentration was clamped at its basal value during the first 60 min of SRIF infusion and then raised to approximately 200 mg/dl by a variable glucose infusion. Plasma insulin levels remained at or below 5 microU/ml during SRIF infusion, including the hyperglycemic period. No appreciable difference between controls and diabetics was present in the basal state as to forearm glucose metabolism. After 60 min of SRIF infusion and euglycemia, forearm glucose uptake fell consistently from 2.1 +/- 0.7 mg X liter-1 X min-1 to 1.0 +/- 0.6 (P less than 0.05) and from 1.7 +/- .2 to 0.4 +/- 0.3 (P less than 0.02) in the control and diabetic groups, respectively. The subsequent induction of hyperglycemia caused a marked increase in both the arterial-deep venous blood glucose difference (P less than 0.02-0.01) and forearm glucose uptake (P less than 0.01-0.005). However, the response in the diabetic group was significantly greater than that observed in controls. The incremental area of forearm glucose uptake was 276 +/- 31 mg X liter-1 X 90 min and 532 +/- 81 in the control and diabetic groups, respectively (P less than 0.02). In the basal state, the forearm released lactate and alanine both in controls and diabetic subjects at comparable rates. No increment was observed after hyperglycemia, despite the elevated rates of glucose uptake. It is concluded that (1) hyperglycemia per se stimulates forearm glucose disposal to a greater extent in type II diabetics than in normal subjects; and (2) the resulting increment of glucose disposal does not accelerate the forearm release of three carbon compounds. The data support the hypothesis that hyperglycemia per se may play a compensatory role for the defective glucose disposal in type II diabetes.