Increase In Plasma Glucagon Concentration Research Articles

Distinct Mechanisms Responsible for the Increase in Glucose Production and Ketone Formation Caused by Empagliflozin in T2DM Patients.

To examine the mechanisms responsible for the increase in glucose and ketone production caused by empagliflozin in patients with type 2 diabetes mellitus (T2DM). Twelve subjects with T2DM participated in two studies performed in random order. In study 1, endogenous glucose production (EGP) was measured with 8-h infusion of 6,6,D2-glucose. Three hours after the start of 6,6,D2-glucose infusion, subjects ingested 25 mg empagliflozin (n = 8) or placebo (n = 4), and norepinephrine (NE) turnover was measured before and after empagliflozin ingestion with 3H-NE infusion. Study 2 was similar to study 1 but performed under pancreatic clamp conditions. When empagliflozin was ingested under fasting conditions, EGP increased by 31% in association with a decrease in plasma glucose (-34 mg/dL) and insulin (-52%) concentrations and increases in plasma glucagon (+19%), free fatty acid (FFA) (+29%), and β-hydroxybutyrate (+48%) concentrations. When empagliflozin was ingested under pancreatic clamp conditions, plasma insulin and glucagon concentrations remained unchanged, and the increase in plasma FFA and ketone concentrations was completely blocked, while the increase in EGP persisted. Total-body NE turnover rate was greater in subjects receiving empagliflozin (+67%) compared with placebo under both fasting and pancreatic clamp conditions. No difference in plasma NE concentration was observed in either study. The decrease in plasma insulin and increase in plasma glucagon concentration caused by empagliflozin is responsible for the increase in plasma FFA concentration and ketone production. The increase in EGP caused by empagliflozin is independent of the change in plasma insulin or glucagon concentrations and is likely explained by the increase in NE turnover.

54-LB: Distinct Mechanisms Are Responsible for the Increase in Endogenous Glucose Production and Ketone Formation following Empagliflozin in T2DM Patients

Aim: To examine the mechanisms responsible for the increase in glucose and ketone production caused by SGLT2 inhibition with empagliflozin in T2DM patients. Research Design and Methods: 12 T2DM subjects (Age = 53; BMI = 31.7; HbA1c = 7.4%) participated in two studies performed in random order. At 0700h following an overnight fast subjects received an 8-hour infusion of 6,6D2-glucose to measure endogenous (hepatic) glucose production. At 0900 h an infusion of 3H-norepinephrine was started. At 1000h subjects ingested 25 mg of empagliflozin (n=8) or matching placebo (n=4) and were followed for 5 hours (1500 h) . Within 1 week subjects returned for a repeat study with pancreatic clamp to maintain plasma insulin and glucagon concentrations constant at the basal level. As per study one, subjects ingested empagliflozin 25 mg or placebo prior to the pancreatic clamp. Results: When empagliflozin was ingested under fasting conditions, EGP increased by 31% in association with a decrease in plasma glucose (-34 mg/dl) and insulin (-52%) concentrations and increases in plasma glucagon (+19%) , FFA (+29%) and β-hydroxybutyrate (β-HB) (+48%) concentrations. When empagliflozin was ingested under pancreatic clamp conditions, plasma insulin and glucagon concentrations remained unchanged, and the increase in plasma FFA and ketone concentrations was completely blocked, while the increase in EGP persisted. Total-body NE turnover rate increased significantly in subjects receiving empagliflozin (+67%) compared to placebo under both fasting and pancreatic clamp conditions. No difference in plasma norepinephrine concentration was observed in either study. Conclusion: The decrease in plasma insulin and increase in plasma glucagon concentration caused by empagliflozin is responsible for the increase in plasma FFA concentration and ketone production. The increase in EGP caused by empagliflozin is independent of the change in plasma insulin or glucagon concentrations and is explained by the increase in total-body NE turnover. Disclosure S. Abdelgani: None. J. M. Adams: None. G. Daniele: n/a. F. Almulla: None. R. A. Defronzo: Advisory Panel; AstraZeneca, Boehringer Ingelheim International GmbH, Intarcia Therapeutics, Inc., Novo Nordisk, Research Support; AstraZeneca, Boehringer Ingelheim International GmbH, Merck & Co., Inc., Speaker’s Bureau; AstraZeneca. M. Abdul-ghani: None. M. Abu-farha: None. S. Del prato: Advisory Panel; Applied Therapeutics, Eli Lilly and Company, Novartis Pharmaceuticals Corporation, Novo Nordisk A/S, Sanofi, Consultant; Menarini Group, Research Support; AstraZeneca, Boehringer Ingelheim International GmbH, Speaker’s Bureau; AstraZeneca, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Merck & Co., Inc., Sanofi, Stock/Shareholder; Novo Nordisk A/S. Funding National Institute of Health, Boehringer Ingelheim provided empagliflozin and placebo

282-OR: The Effect of Glucagon on Rates of Hepatic Mitochondrial Oxidation and Pyruvate Carboxylase Flux in Man Assessed by Positional Isotopomer NMR Tracer Analysis (PINTA)

Dual GLP-1/glucagon agonists are now in clinical trials for the treatment of T2D and NASH. In addition to promoting further reduction in food intake on top of GLP-1, the glucagon component of these dual agonists may also promote increased rates of hepatic mitochondrial fat oxidation. In order to investigate this possibility we assessed the glucagon-specific effects of a dual agonist on rates of hepatic mitochondrial oxidation (VCS) and pyruvate carboxylase flux (VPC) in humans by infusing glucagon to achieve a physiological increase in plasma glucagon concentrations in combination with a novel 13C PINTA method to assess rates of hepatic VCS and VPC in 15 healthy volunteers using a paired study design. Following an overnight fast a 3-h IV infusion of [3-13C]lactate (4.3 μmol/Kg-min) and [1,2,3,4,5,6,6-2H7]glucose (0.22 μmol/Kg-min) was begun and during the last 2 hours glucagon (GLG) was co-infused [6 ng/(Kg-min)] or no GLG (CON). The GLG infusion resulted in a ~2.4 fold increase in plasma GLG conc. (from 75±11 to 183±20 pg/mL; P<0.0001), which was associated with an ~20% increase in both plasma C-peptide (from 1.89±0.17 to 2.30±0.26 ng/mL; P=0.02) and plasma insulin conc. (from 9.9±2.0 to 12.0±2.4 μU/mL; P=0.06). Plasma glucose conc. increased from 4.90±0.16 to 5.64±0.19 mmol/L (P=0.0001) which was associated with a tendency for increased rates of glucose production (CON:1042±123 vs. GLG:1148±122 μmol/min; p=0.086) despite no change in rates of VPC flux (CON: 403±69 vs. GLG: 373±55 μmol/min; p=NS). In contrast, this physiological increase in plasma GLG concentrations caused an 85% increase in rates of hepatic VCS (P<0.05). Conclusion: Taken together these studies demonstrate that a physiological increase in plasma glucagon promotes increased rates of hepatic mitochondrial oxidation in humans, which may provide additional benefits to the anorexic effects of dual GLP-1/glucagon agonists to reduce hepatic steatosis. Disclosure K. Petersen: Advisory Panel; Spouse/Partner; AstraZeneca, iMetabolic Biopharma Corporation, Janssen Research & Development, LLC, Merck & Co., Inc., Consultant; Spouse/Partner; Aegerion Pharmaceuticals Inc., Novo Nordisk, Research Support; Self; Gilead Sciences, Inc., Merck & Co., Inc. G. I. Shulman: Consultant; Self; 89bio, Inc., BridgeBio, Ionis Pharmaceuticals, Maze Therapeutics, Novo Nordisk, Other Relationship; Self; AstraZeneca, Esperion Therapeutics, Inc, Generian Pharmaceuticals, Inc., Gilead Sciences, Inc., iMetabolic Biopharma Corporation, Janssen Research & Development, LLC, Merck & Co., Inc., The Liver Company. Funding Merck & Co., Inc. (MISP583402); National Institutes of Health (R01DK113984)

The Influence Of A Whey Protein Preload Prior To Carbohydrate Consumption On Cycling Performance

INTRODUCTION: The consumption of carbohydrates during a bout of endurance exercise has been shown to promote a glycogen sparing effect and lead to an improvement in exercise performance. The consumption of whey protein prior to a prolonged bout of endurance exercise may augment insulin secretion and further spare muscle glycogen. PURPOSE: To examine if a whey protein solution consumed as a preload prior to a glucose bolus influenced performance and metabolic responses during a cycling performance trial. METHODS: Ten recreationally trained cyclists and triathletes completed two experimental trials. Each participant was required to perform two separate cycling performance tests, which consisted of cycling for 30 min at 90% lactate threshold, followed by a 30 min time trial. Participants consumed a whey protein isolate preload (0.7 g/kg/LBM) or a placebo 20 min prior to the consumption of a glucose beverage (0.9 g/kg/LBM). The glucose beverage was consumed 10 min prior to the cycling performance test. During both trials, plasma glucose, c-peptide, insulin, glucagon, and NEFA concentrations were measured. RESULTS: There were no significant differences in overall time trial performance (WP 16.8 ± 0.34 km; PL 17 ± 0.4 km; p = .346). WP stimulated a significant increase in plasma insulin concentrations at time point 0 (WP = 222.88 ± 45.1 pg/ml; PL = 85.95 ± 45.1 pg/ml; p = .047) compared to the placebo trial. Despite an increase in plasma insulin, there were no significant timepoint differences for plasma glucose. WP stimulated a significant increase in plasma glucagon concentrations for timepoint -10, 0, 15, 30, 45, and 60 when compared to the PL trial (all values p < .05). CONCLUSION: Although there were significant alterations in plasma insulin concentration due to the consumption of the whey protein isolate preload, this did not influence overall cycling performance or substrate utilization. Funding Source: National Strength and Conditioning Association – GNC Sport Nutrition Grant

Glucagon stimulates gluconeogenesis by INSP3R1-mediated hepatic lipolysis.

While it is well-established that alterations in the portal vein insulin/glucagon ratio play a major role in causing dysregulated hepatic glucose metabolism in type 2 diabetes (T2D)1–3, the mechanisms by which glucagon alters hepatic glucose production and mitochondrial oxidation remain poorly understood. Here we show that glucagon stimulates hepatic gluconeogenesis by increasing hepatic adipose triglyceride lipase activity, intrahepatic lipolysis, hepatic acetyl-CoA content, and pyruvate carboxylase flux, while also increasing mitochondrial fat oxidation, mediated by stimulation of the inositol triphosphate receptor-1 (InsP3R-I). Chronic physiological increases in plasma glucagon concentrations increased mitochondrial hepatic fat oxidation and reversed diet-induced hepatic steatosis and insulin resistance in rats and mice; however, the effect of chronic glucagon treatment to reverse hepatic steatosis and glucose intolerance was abrogated in InsP3R-I knockout mice. These results provide new insights into glucagon biology and suggest that InsP3R-I may be a novel therapeutic target to reverse nonalcoholic fatty liver disease and T2D.

288-LB: Effects of the Hepatic Mitochondrial Calcium Uniporter on Hepatic Gluconeogenesis and Mitochondrial Metabolism in Awake Mice

Increased hepatic glucose production, due to increased rates of gluconeogenesis, is a contributor to both fasting and postprandial hyperglycemia in patients with T2D. Recent evidence implicates a role for hepatic calcium signaling in mediating glucagon's effect to stimulate glucose production and mitochondrial oxidation; however, the cellular and molecular mechanisms by which glucagon promotes these alterations remain poorly understood. We hypothesize that an acute physiological increase in plasma glucagon concentrations will increase cytosolic and mitochondrial calcium concentrations, promoting increases in rates of hepatic mitochondrial oxidation and gluconeogenesis in a transcription-independent manner. To test this hypothesis, we used mice with a liver-specific loss of the mitochondrial calcium uniporter (MCU), which is the main transporter that allows rapid transport of calcium into the mitochondrial matrix. We found that glucagon increased oxygen consumption rate by 80% (p&amp;lt;0.0001) in WT hepatocytes, while this effect was abrogated in MCU KO hepatocytes. We also measured hepatic mitochondrial oxidation (VCS) in vivo using Positional Isotopomer NMR Tracer Analysis (PINTA) and found a 74% decrease in VCS (p=0.05) in MCU KO mice compared to WT mice. This suggests that tightly regulated mitochondrial calcium signaling is necessary for regulating hepatic mitochondrial oxidation. Next, we measured intrahepatic lipolysis and hepatic gluconeogenesis in vitro and in vivo. We found that glucagon increased lipolysis (p=0.05) and glucose production (p=0.024) by ∼1.5 fold in MCU KO compared to WT hepatocytes. Furthermore, in vivo PINTA results showed that glucagon increased pyruvate carboxylase flux (VPC) by 68% (p=0.08) in MCU KO mice. Taken together, these results suggest that mitochondrial calcium signaling through MCU is necessary to regulate the effect of glucagon to modulate hepatic gluconeogenesis and mitochondrial oxidation. Disclosure J. Lee: None. L. Goedeke: None. Y. Zhang: None. R.J. Perry: Research Support; Self; AstraZeneca. R. Goodman: None. V. Mootha: Advisory Panel; Self; Janssen Pharmaceuticals, Inc. Consultant; Self; 5AM Ventures. Other Relationship; Self; Raze Therapeutics. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research &amp; Development, Merck &amp; Co., Inc. Advisory Panel; Spouse/Partner; Merck &amp; Co., Inc. Board Member; Self; Novo Nordisk A/S. Consultant; Self; Aegerion Pharmaceuticals, IMetabolic BioPharma Corporation, Longitude Capital, Nimbus Discovery, Inc., Staten Biotechnology B.V. Funding National Institutes of Health

1952-P: Glucagon Receptor Antagonism Increases Plasma Amino Acids and Glucagon

Hyperglucagonemia in type 2 diabetes (T2D) may result from impaired hepatic glucagon signaling and consequent reduced glucagon-induced amino acid (AA) turnover leading to higher AA concentrations and stimulation of glucagon secretion. In a double-blinded, cross-over study, blood was sampled from 10 overnight fasted patients with T2D (BMI [mean±SD]: 33.0±5.4 kg/m2; HbA1c: 46.2±6.1 mmol/mol, 6.4±0.6%) and 10 matched healthy controls (BMI: 31.7±4.2 kg/m2; HbA1c: 33.9±3.0 mmol/mol, 5.3±0.3%) after a single-dose of the glucagon receptor antagonist (GRA) LY2409021 or placebo. Total AA and glucagon concentrations are means of 3 samples (15 minutes apart) on 3 GRA and 3 placebo days. Fractioned AA were analyzed from one sample per day. Total AA concentrations were increased by GRA compared to placebo by 1.4 fold in T2D and 1.3 fold in controls (P≤0.001) with threonine, proline and the glucagonotropic AAs alanine and tyrosine exhibiting the greatest increases in T2D (1.6-2 fold) and controls (1.4-1.5 fold). GRA also increased plasma glucagon concentrations by more than 3-fold (P≤0.0001), and the glucagonotropic AAs alanine (R2 0.24, P=0.0012) and tyrosine (R2 0.30, P=0.0002) were correlated to glucagon. In conclusion, acute inhibition of glucagon receptor signaling by GRA causes hyperaminoacidemia linked to hyperglucagonemia, supporting the importance of the liver-alpha cell axis in regulating circulating glucagon and AA in humans. Disclosure S. Haedersdal: None. N.J. Wewer Albrechtsen: Research Support; Self; Mercodia, Novo Nordisk A/S. Speaker's Bureau; Self; Merck Sharp &amp; Dohme Corp. A.B. Lund: None. K.D. Galsgaard: None. M. Winther-Soerensen: None. J.J. Holst: Advisory Panel; Self; Novo Nordisk A/S. F.K. Knop: Advisory Panel; Self; AstraZeneca, MedImmune, Merck Sharp &amp; Dohme Corp., Mundipharma, Novo Nordisk A/S, Sanofi. Consultant; Self; Amgen Inc., Carmot Therapeutics, Novo Nordisk A/S. Research Support; Self; AstraZeneca, Novo Nordisk A/S. Speaker's Bureau; Self; AstraZeneca, MedImmune, Merck Sharp &amp; Dohme Corp., Mundipharma, Norgine, Novo Nordisk A/S. T. Vilsbøll: None. Funding Novo Nordisk Foundation

Effect of Combination Therapy with Liraglutide plus Canagliflozin on HGP and HbA1c vs. Each Therapy Alone in T2DM

Background: We previously have shown that SGLT2 inhibitors cause an increase in HGP accompanied with an increase in plasma glucagon concentration. We hypothesized that the increase in plasma glucagon concentration is, at least in part, responsible for the increase in HGP. The aim of the present study was to examine whether inhibition of glucagon secretion by liraglutide can prevent the increase in HGP. Research Design and Methods: 51 T2DM patients (age=51±1 yr; 40% female; BMI=34.6±0.7; diabetes duration=6.8±0.8 yr; FPG=175±7; HbA1c=8.3±0.1%) were randomized to receive for 16 weeks: (i) canagliflozin 300 mg; (ii) liraglutide 1.8 mg; or (iii) canagliflozin 300 mg plus liraglutide 1.8 mg. HGP (measured with 3-3H-glucose infusion) and plasma glucagon concentration were measured before and after 16 weeks of treatment. Results: Canagliflozin monotherapy caused a significant reduction in HbA1c (-1.1±0.2%, p&amp;lt;0.01) accompanied with an increase in plasma glucagon concentration (by 28%, p&amp;lt;0.05) and HGP (by 15%, p&amp;lt;0.05) which lasted for 16 weeks. Conversely, liraglutide monotherapy caused a 1.6±0.5% (p&amp;lt;0.01) reduction in HbA1c accompanied by a small (6%) reduction in HGP (P=NS) without significant change in fasting plasma glucagon concentration. The combination of canagliflozin plus liraglutide caused a greater reduction in HbA1c (1.9±0.5%, p&amp;lt;0.vs. canagliflozin and p=NS vs. liraglutide) and attenuated the increase in fasting plasma glucagon and basal HGP at 16 weeks. Conclusion: These results: (1) support a possible role for increased plasma glucagon levels in the long term maintenance of increase in HGP caused by SGLT2i, and (2) suggest that factors other than/in addition to glucagon contribute to the initiation of the increase in HGP. Disclosure M. Abdul-Ghani: None. A.M. Ali: None. R.A. Martinez: None. J.M. Adams: None. E. Cersosimo: Research Support; Self; AstraZeneca, VeroScience, LLC.. Speaker's Bureau; Self; AstraZeneca, Sanofi, Janssen Pharmaceuticals, Inc., Eli Lilly and Company. C.L. Triplitt: Speaker's Bureau; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Eli Lilly and Company. Consultant; Self; Sanofi, Novo Nordisk Inc. R.A. DeFronzo: Speaker's Bureau; Self; AstraZeneca, Novo Nordisk Inc.. Advisory Panel; Self; AstraZeneca, Novo Nordisk Inc., Janssen Pharmaceuticals, Inc., Boehringer Ingelheim Pharmaceuticals, Inc., Elcelyx Therapeutics, Inc., Intarcia Therapeutics, Inc.. Research Support; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Takeda Pharmaceuticals U.S.A., Inc..

Mechanisms by Which Glucagon Acutely Stimulates Hepatic Mitochondrial Oxidation and Gluconeogenesis

Glucagon has been suggested to be both pathogenic and protective against type 2 diabetes (T2D) reflecting our poor understanding of the molecular mechanisms by which glucagon alters hepatic metabolism. Using Positional Isotopomer NMR Tracer Analysis (PINTA) we found that acute glucagon infusion stimulates rates of hepatic gluconeogenesisin glycogen-depleted mice by promoting increases in intrahepatic lipolysis and hepatic acetyl-CoA content (75±6 vs. 101±6 nmol/g, p=0.01), pyruvate carboxylase flux (VPC, 70.9±3.9 vs. 99.9±7.1 µmol/[kg-min], p=0.008) and mitochondrial oxidation (90.0±12.9 vs. 452.1±78.3 µmol/[kg-min], p=0.001) in vivo. Each of these effects was abrogated in liver-specific Inositol Trisphosphate Receptor-I (InsP3R-I) knockout mice demonstrating that intracellular calcium signaling is necessary for these processes. Liver specific knockdown of adipocyte triglyceride lipase abolished acute glucagon stimulation of gluconeogenesis (control 70.5±2.9 vs. 103.3±3.3 µmol/[kg-min], p&amp;lt;0.0001 and ATGL knockdown 69.7±1.7 vs. 69.6±2.0 µmol/[kg-min], p=0.9) and VPC (control 63.3±5.0 vs. 100.0±4.8 µmol/[kg-min], p=0.0003, ATGL knockdown 58.9±4.9 vs. 59.2±3.2 µmol/[kg-min], p=0.9) in WT mice demonstrating the necessity of hepatocellular lipolysis in mediating this process. Chronic increases in plasma glucagon concentrations reversed high fat diet-induced hepatic steatosis (liver triglyceride 50.1±8.5 vs. 28.3±5.1 mg/g, p=0.04; liver membrane diacylglycerol 801±142 vs. 448±47 nmol/g, p=0.03, PKCε membrane/cytosol 1.76±0.40 vs. 0.23±0.04, p=0.0009) and glucose intolerance (GTT glucose AUC 1.44±0.vs. 1.13±0.mM-min, p=0.003, insulin AUC 226.8±18.7 vs. 90.2±11.2 nM-min, p&amp;lt;0.0001). These results provide new insights into glucagon biology and suggest that glucagon and InsP3R-I may be therapeutic targets to reverse nonalcoholic fatty liver disease and T2D. Disclosure R.J. Perry: None. Y. Wang: None. A.L. Brill: None. L. Peng: None. D. Zhang: None. S. Dufour: None. Y. Zhang: None. X. Zhang: None. Y. Nozaki: None. G. Cline: None. B.E. Ehrlich: None. K. Petersen: Research Support; Spouse/Partner; Gilead Sciences, Inc.. Advisory Panel; Spouse/Partner; AstraZeneca, Merck &amp; Co., Inc., Novo Nordisk A/S. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research &amp; Development, Merck &amp; Co., Inc., Novo Nordisk Inc.. Research Support; Self; Gilead Sciences, Inc..

Accumulation of intestinal tissue 3-deoxyglucosone attenuated GLP-1 secretion and its insulinotropic effect in rats.

BackgroundOur recent findings support the idea that 3-deoxyglucosone (3DG), a dietary composition, has been suggested as an independent factor for the development of prediabetes. Secretion of glucagon-like peptide-1 (GLP-1) has been suggested to be impaired in T2DM and in conditions associated with hyperglycemia. Since low oral bioavailability of 3DG has been indicated in a single administration study, in the present study we examined if 3DG is capable of accumulating in intestinal tissue of rats after 2-week administration of 3DG, and the 3DG treatment affects GLP-1 secretion and glucose tolerance.MethodsRats were administered by gastric gavage for 2 weeks. We measured 3DG contents of intestinal tissues (by HPLC), plasma levels of total GLP-1 (by ELISA), insulin and glucagon (both by radioimmunoassay) and blood glucose concentrations. The expressions of the sweet receptor subunits (TAS1R2, TAS1R3) and its downstream molecule TRPM5 in duodenum and colon tissues of rats were quantified by WB. We examined GLP-1 secretion in enteroendocrine STC-1 cells exposured to 3DG.Results3DG treatment for 2 weeks increased 3DG content of intestinal tissues, fasting blood glucose concentration, and reduced plasma concentrations of GLP-1 and insulin at fasting and 15 and 180 min after the glucose load and oral glucose tolerance in conjunction with increased plasma glucagon concentrations. The expressions of TAS1R2, TAS1R3 and TRPM5 were shown to be reduced whereas 3DG treatment did not affect plasma dipeptidyl peptidase-4 activity, indicating an impaired GLP-1 secretion in 3DG-treated rats. This idea was further supported by the fact that exposure to 3DG directly decrease GLP-1 secretion in STC-1.ConclusionIt is the first demonstration that 3DG was capable of accumulating in intestinal tissue and thereby decreased secretion of GLP-1 and insulin in a similar manner. 3DG-treated rats developed impaired glucose regulation (IGR) with obviously pancreatic islet cell dysfunction. It is further concluded that a decrease in the biological function of GLP-1 resulting from the decreased GLP-1 secretion is the most likely mechanism for the impaired insulin secretion, which ultimately promoted the development of IGR. These results will also contribute to a better understanding of the significance for restoring physiological GLP-1 secretion.Electronic supplementary materialThe online version of this article (doi:10.1186/s13098-016-0194-9) contains supplementary material, which is available to authorized users.

Postprandial lipemia induces pancreatic α cell dysfunction characteristic of type 2 diabetes: studies in healthy subjects, mouse pancreatic islets, and cultured pancreatic α cells

Type 2 diabetes is associated with pancreatic α cell dysfunction, characterized by elevated fasting plasma glucagon concentrations and inadequate postprandial glucose- and insulin-induced suppression of glucagon secretion. The cause and the underlying mechanisms of α cell dysfunction are unknown. Because Western dietary habits cause postprandial lipemia for a major part of a day and, moreover, increase the risk of developing type 2 diabetes, we tested the hypothesis that postprandial lipemia with its characteristic elevation of triglyceride-rich lipoproteins (TGRLs) might cause pancreatic α cell dysfunction. In a crossover study with 7 healthy volunteers, 2 experiments using 2 fat-enriched meals were performed on each volunteer; meal 1 was designed to increase plasma concentrations of both TGRLs and nonesterified fatty acids and meal 2 to increase TGRLs only. Intravenous glucose boli were injected at 0800 after an overnight fast and postprandially at 1300, 3 h after ingestion of a fat-enriched meal. Glucagon concentrations were measured throughout the days of the experiments. In addition to the study in humans, in vitro experiments were performed with mouse pancreatic islets and cultured pancreatic alpha TC 1 clone 9 (αTC1c9) cells, which were incubated with highly purified TGRLs. In humans, postprandial lipemia increased plasma glucagon concentrations and led to an inadequate glucose- and insulin-induced suppression of glucagon. There was no difference between the 2 meal types. In mouse pancreatic islets and cultured pancreatic αTC1c9 cells, purified postprandial TGRLs induced abnormalities in glucagon kinetics comparable with those observed in humans. The TGRL-induced α cell dysfunction was due to reduced γ-aminobutyric acid A receptor activation in pancreatic α cells. We concluded that postprandial lipemia induces pancreatic α cell dysfunction characteristic of type 2 diabetes and, therefore, propose that pancreatic α cell dysfunction could be viewed, at least partly, as a postprandial phenomenon.

Central administration of an orexin receptor 1 antagonist prevents the stimulatory effect of Olanzapine on endogenous glucose production

Atypical antipsychotic drugs such as Olanzapine (Olan) induce weight gain and metabolic changes associated with the development of type 2 diabetes. The mechanisms underlying these undesired side-effects are currently unknown. It has been shown that peripheral injections of Olan activate neurons in the lateral hypothalamus/perifornical area and that a large part of these neurons are orexin (Ox) A-positive. We investigated further the possible involvement of the central Ox system in the metabolic side-effects of Olan by comparing the hyperglycaemic effects of an intragastric (IG) Olan infusion between animals treated intracerebroventricularly (ICV) with an Ox-1 receptor antagonist (SB-408124) or vehicle. As observed in previous studies IG Olan caused an increase in blood glucose, endogenous glucose production and plasma glucagon levels. ICV pre-treatment with the Ox-1 receptor antagonist did not affect the Olan-induced hyperglycaemia or increased plasma glucagon concentrations, but the increased endogenous glucose production was blunted by the ICV SB-408124 treatment. From these results we conclude that the metabolic side-effects of Olan are partly mediated by the hypothalamic Ox system.

Hormonal responses associated with the nadir in blood glucose during graded cycling exercise

The response of glucoregulatory hormones associated with the nadir in serum glucose (i.e., glucose threshold) was examined during graded exercise to exhaustion in 22 physically active male participants. A comparison was also made between the glucose, lactate, and ventilatory thresholds. The mean (±SD) age, height, and body mass of the participants was 24.5 (±4.0) years, 182.0 (±9.1) cm, and 84.8 (±17.4) kg, respectively. Blood samples were collected at rest and during the final minute of each power output of a graded exercise test. The nadir in blood glucose concentration occurred at the same time as the lowest concentration of plasma glucagon, and both were significantly elevated at maximal exercise. Insulin response showed a significant decrease from rest but was maintained prior to the glucose nadir followed by a significant decrease. Cortisol was significantly elevated at maximal exercise intensity only. There was no difference in the power output and oxygen consumption (VO2) at the glucose and lactate thresholds but both occurred at one power output prior to the ventilatory threshold. In conclusion, a nadir in serum glucose occurred in a predictable fashion in relation to other measures of anaerobic threshold. The nadir in blood glucose occurred prior to an increase in plasma glucagon concentration and a decrease in circulating insulin concentration during the re-establishment of euglycemia during graded exercise.

長時間運動時の血中グルコース濃度に及ぼすタウリン投与の影響

To determine the effect of taurine on blood glucose concentration during prolonged exercise, fifteen male university students cycled for 120 min at 50%VO2max after 7 days with or without taurine supplementation. Exercise tended to reduce the blood glucose concentration, whereas taurine significantly prevented this decline. Exercise significantly increased plasma glucagon concentrations in both groups to a similar degree. Serum insulin concentrations did not differ during exercise under both conditions. Taurine supplementation respectively significantly inhibited and tended to inhibit the plasma noradrenaline and adrenaline concentrations increased by exercise. These results suggest that taurine supplementation can maintain the blood glucose concentration during prolonged exercise through enhanced catecholamine sensitivity.

Effects of Dexamethasone and Growth Hormone Treatment on Hepatic Gluconeogenic Enzymes in Calves

The hypothesis was tested that dexamethasone (DX) and bovine somatotropin (bST) alter expression or activity of gluconeogenic enzymes in neonatal calves. Holstein dairy calves (n=24) were randomly divided in 4 groups and were treated with saline (control group), with DX at 30μg/kg body weight per d (CDX), with 500mg of sustained-release recombinant bST every 14 d (CbST), and with the combination of DX and bST from d 3 through 42 of life (CbSTDX). Plasma glucose and insulin concentrations were elevated throughout the study in CbSTDX, and insulin concentrations were elevated in CDX from d 7 to 28. Treatment with DX and the combination of DX and bST increased plasma glucagon concentrations from d 14 to 42, but decreased plasma cortisol concentrations on d 7 and 14 when compared with control calves. In liver, phosphoenolpyruvate carboxykinase (PEPCK) mRNA levels were reduced in CDX and CbSTDX when compared with control calves or CbST. The activity of PEPCK on d 14 was higher in CbSTDX compared with control calves. Pyruvate carboxylase mRNA levels were decreased on d 7 in CDX and CbSTDX. Pyruvate carboxylase activities on d 14 and 28 were lower in CDX and CbSTDX than in control calves or CbST. These data indicate an age-dependent response to DX for blood metabolites, expression and activities of hepatic PEPCK and pyruvate carboxylase, and for effects of bST, suggesting that glucocorticoid status is important.

Alterations in hepatic glucagon receptor density and in Gsα and Giα2protein content with diet-induced hepatic steatosis: effects of acute exercise

The present study was undertaken to test the hypothesis that a high-fat diet-induced liver lipid infiltration is associated with a reduction of hepatic glucagon receptor density (B(max)) and affinity (K(d)), and with a decrease in stimulatory G protein (G(s)alpha) content while enhancing inhibitory G protein (G(i)alpha(2)) expression. We also hypothesized that, under this dietary condition, a single bout of endurance exercise would restore hepatic glucagon receptor parameters and G protein expression to standard levels. Female Sprague-Dawley rats were fed either a standard (SD) or a high-fat diet (HF; 40% kcal) for 2 wk (n = 20 rats/group). Each dietary group was thereafter subdivided into a nonexercised (Rest) and an acute-exercised group (Ac-Ex). The acute exercise consisted of a single bout of endurance exercise on a treadmill (30 min, 26 m/min, and 0% slope) immediately before being killed. The HF compared with the SD diet was associated with significantly (P < 0.05) higher values in hepatic triglyceride concentrations (123%), fat pad weight, and plasma free fatty acid (FFA) concentrations. The HF diet also resulted in significantly (P < 0.05) lower hepatic glucagon receptor density (45%) and G(s)alpha protein content (75%), as well as higher (P < 0.05) G(i)alpha(2) protein content (27%), with no significant effects on glucagon receptor affinity. Comparisons of all individual liver triglyceride and B(max) values revealed that liver triglycerides were highly (P < 0.003) predictive of the decreased glucagon receptor density (R = -0.512). Although the 30-min exercise bout resulted in some typical exercise effects (P < 0.05), such as an increase in FFA (SD diet), a decrease in insulin levels, and an increase in plasma glucagon concentrations (SD diet), it did not change any of the responses related to liver glucagon receptors and G proteins, with the exception of a significant (P < 0.05) decrease in G(i)alpha(2) protein content under the HF diet. The present results indicate that the feeding of an HF diet is associated with a reduction in plasma membrane hepatic glucagon receptor density and G(s)alpha protein content, which is not attenuated by a 30-min exercise bout. It is suggested that liver lipid infiltration plays a role in reducing glucagon action in the liver through a reduction in glucagon receptor density and glucagon-mediated signal transduction.

The role of corticosterone in the metabolic recovery after intrasplenic adrenal autotransplantation in rats.

Transplantation of adrenal cortical tissue may represent an alternative treatment to reestablish glucocorticoid secretion in adrenal insufficiency. In the present work, performed in adrenalectomized rats and adrenalectomized rats with a complete autotransplanted adrenal into the spleen, several hormones and biochemical parameters were measured and compared to control animals, in order to examine hormone interactions. Rats were sacrificed three weeks after surgery, and plasma and tissue samples were obtained for hormone and biochemical measurements. In adrenalectomized animals, plasma corticosterone, aldosterone and insulin levels were profoundly decreased, whereas in autotransplanted rats plasma corticosterone levels showed a partial recovery, aldosterone plasma concentrations remained low, and plasma insulin levels increased to values close to those of the controls. Both groups showed a marked elevation of plasma ACTH levels, as well as significantly increased plasma glucagon concentrations. In autotransplanted animals, most of the biochemical parameters, which were altered in adrenalectomized rats, returned to normal levels. These results suggest that increased glucagon levels in adrenalectomized and autotransplanted animals, may contribute to the marked increase of plasma ACTH, and could also be important in the recovery of plasma glucose and hepatic glycogen observed in autografted rats. Since high glucagon concentrations alone were unable to normalize carbohydrate levels in adrenalectomized animals, it appears that glucagon can act only in the presence of corticosterone.

TNF directly stimulates glucose uptake and leucine oxidation and inhibits FFA flux in conscious dogs.

We tested the hypothesis that the metabolic changes in glucose, lipid, and protein metabolism seen during tumor necrosis factor (TNF) infusion were due to the increase in plasma glucagon concentration rather than to the direct effects of TNF. We employed a pancreatic clamp technique to keep plasma insulin and glucagon concentrations constant throughout a 4-h isotope infusion. Glucose, lipid, and protein kinetics were measured by means of the primed, constant infusion of [6,6-2H]glucose, [2H5]glycerol, [2H2]palmitic acid, and [1-13C]leucine. After a 2-h baseline period (period 1), TNF was infused as a primed, constant infusion (prime, 2.5 micrograms/kg; constant infusion, 62.5 ng.kg-1.min-1) for 2 h (period 2). Whereas plasma glucose concentration dropped significantly during TNF infusion, endogenous glucose production did not change. The decrease in glucose concentrations was due to a stimulation of glucose clearance (P < 0.05). The rate of lipolysis did not decrease significantly, but free fatty acid (FFA) flux and plasma FFA concentration significantly decreased during TNF infusion (P < 0.05). The rate of appearance of leucine was not affected by TNF infusion, but TNF caused a significant increase in 13CO2 excretion (P < 0.05) and leucine oxidation (P < 0.05). The calculated rates of whole body protein synthesis decreased. We concluded that TNF did not directly affect glucose production. Furthermore, changes in protein and lipid kinetics during TNF infusion were not mediated by changes in insulin or glucagon and may have reflected direct effects of TNF.

Increased nonoxidative glucose metabolism in idiopathic reactive hypoglycemia

Idiopathic reactive hypoglycemia (IRH) is responsible for postprandial hypoglycemia. Normal insulin secretion and reduced response of glucagon to acute hypoglycemia, but mostly increased insulin sensitivity, represent the metabolic features of this syndrome. The present study has two aims: first, to investigate the fate of glucose utilization inside the cells to assess whether increased glucose disposal in IRH is due to the oxidative and/or nonoxidative pathway; and second, to evaluate glucagon response to prolonged insulin-induced hypoglycemia. In eight patients with IRH and eight normal (N) subjects, we performed two studies on different days: (1) 120-minute euglycemic-hyperinsulinemic (1.0 mU · kg −1 · min −1 regular human insulin) clamp associated with indirect calorimetry; and (2) 180-minute hypoglycemic (2.22 to 2.49 mmo/L achieved through 0.85 mU · kg −1 · min −1 intravenous [IV] regular human insulin) clamp. The results showed an increased insulin-mediated glucose uptake in IRH (9.10 ± 0.19 v 6.78 ± 0.18 mg · kg −1 · min −1, P < .005). Glucose oxidation was similar in IRH subjects and controls both in basal conditions (1.39 ± 0.16 v 1.42 ± 0.15 mg · kg −1 · min −1) and during the clamp studies (2.57 ± 0.21 v 2.78 ± 0.26 mg · kg −1 · min −1). In contrast, nonoxidative glucose disposal was significantly higher in IRH than in N subjects (6.53 ± 0.30 v 4.00 ± 0.21 mg · kg −1 · min −1, P < .001). During insulinization, fat oxidation was reduced slightly more in IRH than in control subjects. During the hypoglycemic clamp, a significant ( P < .01) increase in plasma glucagon concentrations was observed in normal subjects as compared with baseline, whereas no change occurred in IRH patients. In conclusion, in IRH: (1) increased insulin-mediated glucose disposal is due to the increase of nonoxidative glucose metabolism; and (2) glucagon secretion has been confirmed to be inadequate. The increase of insulin sensitivity associated with a deficiency in glucagon secretion can widely explain the occurrence of hypoglycemia in the late postprandial phase.

A lack of a direct action of glucagon on kidney metabolism, hemodynamics, and renal sodium handling in the dog

Although several reports suggest that pharmacologic amounts of glucagon may promote natriuresis, the influence of a physiological or even pathophysiological increase in circulating glucagon levels on kidney function has never been convincingly demonstrated. The present study was therefore undertaken to determine whether a moderate increase in plasma glucagon concentration of blood perfusing the kidney may influence kidney function and promote urinary sodium excretion. To this end, glucagon was infused directly into one renal artery of anesthetized dogs at a rate of 1 ng · kg −1 · min −1, calculated to increase glucagon concentration in the blood perfusing the kidney within the pathophysiologic range and thus to levels seen in some catabolic states such as poorly controlled diabetes or starvation. The contralateral kidney was infused with saline only. The estimated concentration of glucagon in blood perfusing the hormone-infused kidney increased with glucagon infusion from 227 pg · mL −1 during the control period to mean of 779 pg · mL −1. There was a significant increase in glucagon extraction by this kidney, from 33% in baseline conditions to 61% upon intrarenal infusion of the hormone, and hence venous glucagon levels were only slightly higher than in the contralateral kidney. Despite a more than threefold increase in glucagon levels in blood perfusing the hormone-infused kidney versus the contralateral kidney, this experimentally induced hyperglucagonemia was without influence on renal plasma flow (RPF), glomerular filtration rate (GFR), renal vascular resistance, renal uptake of oxygen and energy-providing substrates. Excretion of Na +, K +, Cl −, and PO 4 3− was likewise unaffected. These results indicate that hyperglucagonemia, at least of a magnitude comparable to that seen in starvation or diabetic decompensation, is devoid of any detectable direct influence on renal hemodynamics or tubular function.