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Wade NM, Skiba-Cassy S, Dias K, Glencross BD. Postprandial molecular responses in the liver of the barramundi, Lates calcarifer. FISH PHYSIOLOGY AND BIOCHEMISTRY 2014; 40:427-43. [PMID: 23990285 DOI: 10.1007/s10695-013-9854-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 08/21/2013] [Indexed: 05/25/2023]
Abstract
The regulation of gene expression by nutrients is an important mechanism governing energy storage and growth in most animals, including fish. At present, very few genes that regulate intermediary metabolism have been identified in barramundi, nor is there any understanding of their nutritional regulation. In this study, a partial barramundi liver transcriptome was assembled from next-generation sequencing data and published barramundi EST sequences. A large number of putative metabolism genes were identified in barramundi, and the changes in the expression of 24 key metabolic regulators of nutritional pathways were investigated in barramundi liver over a time series immediately after a meal of a nutritionally optimised diet for this species. Plasma glucose and free amino acid levels showed a mild postprandial elevation which peaked 2 h after feeding, and had returned to basal levels within 4 or 8 h, respectively. Significant activation or repression of metabolic nuclear receptor regulator genes were observed, in combination with activation of glycolytic and lipogenic pathways, repression of the final step of gluconeogenesis and activation of the Akt-mTOR pathway. Strong correlations were identified between a number of different metabolic genes, and the coordinated co-regulation of these genes may underlie the ability of this fish to utilise dietary nutrients. Overall, these data clearly demonstrate a number of unique postprandial responses in barramundi compared with other fish species and provide a critical step in defining the response to different dietary nutrient sources.
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Affiliation(s)
- Nicholas M Wade
- Division of Marine and Atmospheric Research, Ecosciences Precinct, CSIRO Food Futures Flagship, Dutton Park, QLD, 4102, Australia,
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Dai W, Panserat S, Mennigen JA, Terrier F, Dias K, Seiliez I, Skiba-Cassy S. Post-prandial regulation of hepatic glucokinase and lipogenesis requires the activation of TORC1 signalling in rainbow trout (Oncorhynchus mykiss). ACTA ACUST UNITED AC 2013; 216:4483-92. [PMID: 24031053 DOI: 10.1242/jeb.091157] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
To assess the potential involvement of TORC1 (target of rapamycin complex 1) signalling in the regulation of post-prandial hepatic lipid and glucose metabolism-related gene expression in trout, we employed intraperitoneal administration of rapamycin to achieve an acute inhibition of the TOR pathway. Our results reveal that rapamycin inhibits the phosphorylation of TORC1 and its downstream effectors (S6K1, S6 and 4E-BP1), without affecting Akt and the Akt substrates Forkhead-box Class O1 (FoxO1) and glycogen synthase kinase 3α/β (GSK 3α/β). These results indicate that acute administration of rapamycin in trout leads to the inhibition of TORC1 activation. No effect is observed on the expression of genes involved in gluconeogenesis, glycolysis and fatty acid oxidation, but hepatic TORC1 inhibition results in decreased sterol regulatory element binding protein 1c (SREBP1c) gene expression and suppressed fatty acid synthase (FAS) and glucokinase (GK) at gene expression and activity levels, indicating that FAS and GK activity is controlled at a transcriptional level in a TORC1-dependent manner. This study demonstrates for the first time in fish that post-prandial regulation of hepatic lipogenesis and glucokinase in rainbow trout requires the activation of TORC1 signalling.
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Affiliation(s)
- Weiwei Dai
- INRA, UR 1067 Nutrition, Metabolism, Aquaculture, Aquapôle, CD 918, F-64310 Saint-Pée-sur-Nivelle, France
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Seiliez I, Médale F, Aguirre P, Larquier M, Lanneretonne L, Alami-Durante H, Panserat S, Skiba-Cassy S. Postprandial regulation of growth- and metabolism-related factors in zebrafish. Zebrafish 2013; 10:237-48. [PMID: 23659367 DOI: 10.1089/zeb.2012.0835] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Zebrafish (Danio rerio) have been proposed as a possible model organism for nutritional physiology. However, this potential has not yet been realized and studies on the field remain scarce. In this work, we investigated in this species the effect of a single meal as well as that of an increase in the ratio of dietary carbohydrates/proteins on the postprandial expression of several hepatic and muscle metabolism-related genes and proteins. Fish were fed once either a commercial diet (experiment 1) or one of two experimental diets (experiment 2) containing different protein and carbohydrate levels after 72 h of starvation. Refeeding induced the postprandial expression of genes of glycolysis (GK, HK1) and lipogenesis (FAS, G6PDH, ACCa) and inhibited those of gluconeogenesis (cPEPCK) and beta-oxidation (CPT1b) in the viscera. In the muscle, refeeding increased transcript levels of myogenesis (Myf5, Myogenin), inhibited those of Ub-proteasomal proteolytic system (Atrogin1, Murf1a, Murf1b), and induced the activation of key signaling factors of protein synthesis (Akt, 4EBP1, S6K1, S6). However, diet composition had a low impact on the studied factors. Together, these results highlight some specificity of the zebrafish metabolism and demonstrate the interest and the limits of this species as a model organism for nutritional physiology studies.
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Affiliation(s)
- Iban Seiliez
- Institut National de la Recherche Agronomique , UR1067 Nutrition Métabolisme Aquaculture, St-Pée-sur-Nivelle, France.
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Proteomic characterization in the hippocampus of prenatally stressed rats. J Proteomics 2012; 75:1764-70. [DOI: 10.1016/j.jprot.2011.12.017] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 12/09/2011] [Accepted: 12/12/2011] [Indexed: 12/12/2022]
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Kim J, Saidel GM, Kalhan SC. Regulation of Adipose Tissue Metabolism in Humans: Analysis of Responses to the Hyperinsulinemic-Euglycemic Clamp Experiment. Cell Mol Bioeng 2011; 4:281-301. [PMID: 23646067 DOI: 10.1007/s12195-011-0162-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The suppression of lipolysis is one of the key metabolic responses of the adipose tissue during hyperinsulinemia. The failure to respond and resulting increase in plasma fatty acids could contribute to the development of insulin resistance and perturbations in the fuel homeostasis in the whole body. In this study, a mechanistic, computational model of adipose tissue metabolism in vivo has been enhanced to simulate the physiological responses during hyperinsulinemic-euglycemic clamp experiment in humans. The model incorporates metabolic intermediates and pathways that are important in the fed state. In addition, it takes into account the heterogeneity of triose phosphate pools (glycolytic vs. glyceroneogenic), within the adipose tissue. The model can simulate not only steady-state responses at different insulin levels, but also concentration dynamics of major metabolites in the adipose tissue venous blood in accord with the in vivo data. Simulations indicate that (1) regulation of lipoprotein lipase (LPL) reaction is important when the intracellular lipolysis is suppressed by insulin; (2) intracellular diglyceride levels can affect the regulatory mechanisms; and (3) glyceroneogenesis is the dominant pathway for glycerol-3-phosphate synthesis even in the presence of increased glucose uptake by the adipose tissue. Reduced redox and increased phosphorylation states provide a favorable milieu for glyceroneogenesis in response to insulin. A parameter sensitivity analysis predicts that insulin-stimulated glucose uptake would be more severely affected by impairment of GLUT4 translocation and glycolysis than by impairment of glycogen synthesis and pyruvate oxidation. Finally, simulations predict metabolic responses to altered expression of phosphoenolpyruvate carboxykinase (PEP-CK). Specifically, the increase in the rate of re-esterification of fatty acids observed experimentally with the overexpression of PEPCK in the adipose tissue would be accompanied by the up-regulation of acyl Co-A synthase.
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Affiliation(s)
- Jaeyeon Kim
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA ; Center for Modeling Integrated Metabolic Systems, Case Western Reserve University, Cleveland, OH 44106, USA ; Department of Pathobiology, Lerner Research Institute, NE4-203, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA
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Okar DA, Wu C, Lange AJ. Regulation of the regulatory enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. ACTA ACUST UNITED AC 2004; 44:123-54. [PMID: 15581487 DOI: 10.1016/j.advenzreg.2003.11.006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- David A Okar
- Veterans Administration Medical Center, One Veterans Drive, Minneapolis, MN 55417, USA
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Wu C, Okar DA, Newgard CB, Lange AJ. Increasing fructose 2,6-bisphosphate overcomes hepatic insulin resistance of type 2 diabetes. Am J Physiol Endocrinol Metab 2002; 282:E38-45. [PMID: 11739081 DOI: 10.1152/ajpendo.2002.282.1.e38] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Hepatic glucose production is increased as a metabolic consequence of insulin resistance in type 2 diabetes. Because fructose 2,6-bisphosphate is an important regulator of hepatic glucose production, we used adenovirus-mediated enzyme overexpression to increase hepatic fructose 2,6-bisphosphate to determine if the hyperglycemia in KK mice, polygenic models of type 2 diabetes, could be ameliorated by reduction of hepatic glucose production. Seven days after treatment with virus encoding a mutant 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase designed to increase fructose 2,6-bisphosphate levels, plasma glucose, lipids, and insulin were significantly reduced in KK/H1J and KK.Cg-A(y)/J mice. Moreover, high fructose 2,6-bisphosphate levels downregulated glucose-6-phosphatase and upregulated glucokinase gene expression, thereby reversing the insulin-resistant pattern of hepatic gene expression of these two key glucose-metabolic enzymes. The increased hepatic fructose 2,6-bisphosphate also reduced adiposity in both KK mice. These results clearly indicate that increasing hepatic fructose 2,6-bisphosphate overcomes the impairment of insulin in suppressing hepatic glucose production, and it provides a potential therapy for type 2 diabetes.
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Affiliation(s)
- Chaodong Wu
- Department of Biochemistry, Molecular Biology and Biophysics, Medical School, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Carrillo JJ, Ibares B, Esteban-Gamboa A, Felíu JE. Involvement of both phosphatidylinositol 3-kinase and p44/p42 mitogen-activated protein kinase pathways in the short-term regulation of pyruvate kinase L by insulin. Endocrinology 2001; 142:1057-64. [PMID: 11181519 DOI: 10.1210/endo.142.3.7992] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Pyruvate kinase L (PK-L) is a key regulatory enzyme of the hepatic glycolytic/gluconeogenic pathway that can be dephosphorylated and activated in response to insulin. However, the signaling cascades involved in this insulin effect have not been established. In this work we have investigated the potential involvement of phosphatidylinositol 3-kinase (PI 3-K) and p44/p42 mitogen-activated protein kinase (MAPK) pathways in the short-term modulation of PK-L by insulin in primary cultures of rat hepatocytes. Wortmannin, at a concentration of 100 nM, caused a marked inhibition of the PI 3-K/protein kinase B pathway, which became complete at 500 nM wortmannin. Likewise, wortmannin at 100 and 500 nM, elicited partial and total inhibitions of insulin-mediated activation of PK-L, respectively. However, this PI 3-K inhibitor also reduced insulin-mediated phosphorylation of p44/p42 MAPK in cultured rat hepatocytes, indicating that both the PI 3-K and MAPK pathways could be involved in PK-L activation by insulin. Three facts appear to reinforce this hypothesis: 1) the selective and complete inhibition of the PI 3-K/protein kinase B pathway by LY294002 (50 microM) was accompanied by a partial blockade of insulin-induced PK-L activation; 2) when signaling through the MAPK cascade was selectively suppressed by the presence of PD98059 (50 microM), a 50% reduction of insulin-induced activation of PK-L was observed; and 3) the effect of PD98059 (50 microM) on PK-L activation was reinforced by the additional presence of 100 nM wortmannin. We also observed that the blockade of p70 S6-kinase by rapamycin did not affect the activation of PK-L by insulin. From these findings it can be concluded that both PI 3-K and MAPK pathways, but not p70 S6-kinase, are involved in the short-term activation of PK-L by insulin in rat hepatocytes.
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Affiliation(s)
- J J Carrillo
- Department of Biochemistry, Faculty of Medicine, Universidad Autónoma de Madrid, 28029 Madrid, Spain
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Chida Y, Ohtsu H, Takahashi K, Sato K, Toyomizu M, Akiba Y. Carbohydrate metabolism in temporal and persistent hypoglycemic chickens induced by insulin infusion. Comp Biochem Physiol C Toxicol Pharmacol 2000; 126:187-93. [PMID: 11050690 DOI: 10.1016/s0742-8413(00)00111-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In order to elucidate the regulatory mechanism of blood glucose concentrations specific to chickens, carbohydrate metabolism in the liver, muscle and kidney and metabolite concentrations in the blood were investigated in chickens with acute and persistent hypoglycemia. Acute and persistent hypoglycemia were experimentally induced by a single injection of insulin (8 U/kg BW) or by continuous infusion of insulin (22.5 U/kg BW/day) for 4 days. Non-esterified fatty acid (NEFA) concentration in plasma and D-3-hydroxybutyrate (3HB) concentrations in liver and muscle increased in the acute hypoglycemia. Plasma NEFA concentration and 3HB concentration in the blood and liver were not changed at day 3 of persistent hypoglycemia, while 3HB concentration in the muscle was decreased. Phosphofructokinase (PFK) activity in the liver tended to increase but PFK and pyruvate kinase (PK) activities were unchanged in acute hypoglycemia. In persistent hypoglycemia, increase of hepatic PFK activity at day 1 in which it was reversed at day 3, and a small increase of muscle PK activity were observed, while PK and phosphoenolpyruvate carboxykinase (PEPCK) activities in the liver and kidney were not significantly changed. These results show that in the persistent hypoglycemic chickens, hepatic glycolysis transiently increases, which is followed by a small decrease, while glycolysis in muscles and gluconeogenesis in the liver and kidney are not significantly changed.
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Affiliation(s)
- Y Chida
- Laboratory of Animal Nutrition, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan
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Guignot L, Mithieux G. Mechanisms by which insulin, associated or not with glucose, may inhibit hepatic glucose production in the rat. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:E984-9. [PMID: 10600785 DOI: 10.1152/ajpendo.1999.277.6.e984] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated the intrahepatic mechanisms by which insulin, associated or not with hyperglycemia, may inhibit hepatic glucose production (HGP) in the rat. After a hyperinsulinemic euglycemic clamp in postabsorptive (PA) anesthetized rats, the 70% inhibition of HGP could be explained by a dramatic decrease in the glucose 6-phosphate (G-6-P) concentration, whereas the glucose-6-phosphatase (G-6-Pase) and glucokinase (GK) activities were unchanged. Under hyperinsulinemic hyperglycemic condition, the GK flux was increased. The G-6-P concentration was not or only weakly decreased. The inhibition of HGP involved a significant 25% inhibition of the G-6-Pase activity. Under similar conditions in fasted rats, the GK flux was very low. The suppression of G-6-Pase and HGP did not occur, despite plasma insulin and glucose concentrations similar to those in PA rats. Therefore, 1) insulin suppresses HGP in euglycemia by solely decreasing the G-6-P concentration; 2) when combining both hyperinsulinemia and hyperglycemia, the suppression of HGP involves the inhibition of the G-6-Pase activity; and 3) a sustained glucose-phosphorylation flux might be a crucial determinant in the inhibition of G-6-Pase and of HGP.
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Affiliation(s)
- L Guignot
- Institut National de la Santé et de la Recherche Médicale U.449, Faculté de Médecine René Theóphile Hyacinthe Laennec, F-69372 Lyon Cedex 08, France
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Sánchez-Gutierrez JC, Sánchez-Arias JA, Samper B, Felíu JE. Modulation of epinephrine-stimulated gluconeogenesis by insulin in hepatocytes isolated from genetically obese (fa/fa) Zucker rats. Endocrinology 1997; 138:2443-8. [PMID: 9165034 DOI: 10.1210/endo.138.6.5174] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Genetically obese (fa/fa) Zucker rats present an impaired response of hepatic glucose production to the inhibition by insulin. In this work, we have investigated the modulation by this hormone of epinephrine-stimulated gluconeogenesis, in hepatocytes isolated from obese (fa/fa) rats and their lean (Fa/-) littermates. Epinephrine (1 microM) caused a maximal stimulation of [14C]lactate conversion to [14C]glucose in hepatocytes isolated from either obese or lean animals. The stimulation of gluconeogenesis by epinephrine was accompanied by a significant reduction of fructose 2,6-bisphosphate levels, an inactivation of both pyruvate kinase and 6-phosphofructo 2-kinase, and by a 2-fold increase in the cellular concentrations of cAMP. The presence of insulin in the incubation medium antagonized, in a concentration-dependent manner, the effects of epinephrine. In hepatocytes isolated from lean rats, the reversion caused by insulin was complete, the concentration required for half-maximal insulin action ranging from 0.22 to 0.56 nM. In contrast, in obese rat hepatocytes, insulin only partially blocked epinephrine-mediated effects, and the sensitivity to insulin was 2- to 4-fold lower, as indicated by the corresponding half-maximal insulin action values. Furthermore, insulin (10 nM) almost completely blocked the increase in cAMP levels induced by epinephrine in lean rat hepatocytes, whereas it only provoked a small and nonsignificant reduction of epinephrine-stimulated levels of the cyclic nucleotide in hepatocytes obtained from obese rats.
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Affiliation(s)
- J C Sánchez-Gutierrez
- Hospital Puerta de Hierro, Departamento de Bioquímica, Facultad de Medicina, Universidad Autónoma de Madrid, Spain
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Massillon D, Chen W, Hawkins M, Liu R, Barzilai N, Rossetti L. Quantitation of hepatic glucose fluxes and pathways of hepatic glycogen synthesis in conscious mice. THE AMERICAN JOURNAL OF PHYSIOLOGY 1995; 269:E1037-43. [PMID: 8572194 DOI: 10.1152/ajpendo.1995.269.6.e1037] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Mice were studied with the euglycemic hyperinsulinemic and the hyperglycemic clamp techniques after a 6-h fast: 1) euglycemic (6.7 +/- 0.2 mM) hyperinsulinemia (approximately 800 microU/ml); 2) hyperglycemic (15.3 +/- 0.4 mM) hyperinsulinemia (approximately 800 microU/ml). All mice received an infusion of [3-3H]glucose and [U-14C]lactate. Basal hepatic glucose production (HGP) averaged approximately 170 mumol.kg-1.min-1 in both groups. During euglycemic and hyperglycemic hyperinsulinemia, HGP decreased by 53% (to 76.7 +/- 11.1 mumol.kg-1.min-1; P < 0.01) and 74% (to 43.3 +/- 7.2 mumol.kg-1.min-1; P < 0.01), respectively. Hyperglycemia increased glucose cycling (by 2.1-fold; P < 0.01) and the contribution of gluconeogenesis to HGP (88 vs. 43%; P < 0.01) while decreasing that of glycogenolysis (12 vs. 57%; P < 0.01). The percentage of neosynthetized hepatic glycogen formed via the direct pathway was markedly increased during hyperglycemia (53 +/- 2% vs. 23 +/- 3%; P < 0.01): These data indicate that the assessment of hepatic glucose fluxes can be accomplished in conscious unrestrained mice and that, in the presence of hyperinsulinemia, hyperglycemia causes 1) a further inhibition of HGP mainly via inhibition of glycogenolysis and increase in hepatic glucose cycling; and 2) about a fivefold stimulation in the direct pathway of hepatic glycogen formation.
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Affiliation(s)
- D Massillon
- Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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Barrett EJ, Bevilacqua S, DeFronzo RA, Ferrannini E. Glycogen turnover during refeeding in the postabsorptive dog: implications for the estimation of glycogen formation using tracer methods. Metabolism 1994; 43:285-92. [PMID: 8139475 DOI: 10.1016/0026-0495(94)90094-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Recent 13C nuclear magnetic resonance (13C-NMR) studies in the anesthetized rat and perfused liver suggest that hepatic glycogen is simultaneously synthesized and degraded, even during combined hyperglycemia and hyperinsulinemia. The presence of glycogen turnover would confound efforts to study glycogen repletion with the use of tracer methods during feeding, particularly if the liver is not glycogen-depleted. To ascertain whether glycogen turnover occurs during normal feeding, we measured liver uptake of glucose in 10 awake, healthy, postabsorptive dogs with long-term arterial, portal, and hepatic venous catheters before and for 3 hours after a meal of either glucose alone (1.5 g/kg) or glucose supplemented with crystalline amino acids (0.7 g/kg); the meal was labeled with D-[3-3H]glucose and [U-14C]alanine. Liver glycogen level was measured in biopsies obtained before and at 180 minutes after the meal. The postabsorptive liver glycogen content was 4.3 +/- 0.9 g/100 g, and net hepatic glucose release averaged 1.8 +/- 0.3 mg/min/kg. Over the 3 hours following feeding, the liver took up glucose (0.37 +/- 0.14 and 0.33 +/- 0.16 g/kg body weight in dogs receiving glucose and glucose with amino acids, respectively). At 3 hours, glycogen synthesis from D-[3-3H]glucose in the two groups averaged 0.24 +/- 0.09 and 0.22 +/- 0.05 g/kg, or approximately 15% of the ingested glucose load. 14C-glucose also was found in liver glycogen, demonstrating ongoing hepatic gluconeogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- E J Barrett
- Department of Internal Medicine, University of Virginia School of Medicine, Charlottesville 22908
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Abstract
Both insulin and hyperglycemia can effectively suppress hepatic glucose output (HGO). We examined whether insulin and hyperglycemia specifically suppress liver net glycogen breakdown in a rat model in which glycogen is the major source of HGO. We further examined whether insulin and hyperglycemia act by similar or distinct enzymatic mechanisms. HGO, the rate of net glycogen loss, and glycogen phosphorylase and synthase activities were measured in fed, anesthetized rats infused with saline or insulin (7 mU/min/kg) while either maintaining plasma glucose at basal (7.8 +/- 0.2 mmol/L, euglycemic clamp [EC]) or at 10 mmol/L above basal (18 +/- 0.4 mmol/L, hyperglycemic clamp [HC]). During the basal period, the rate of HGO in each group was comparable to the rate of net glycogen breakdown, averaging 76 +/- 9 and 75 +/- 5 mumol/min/kg, respectively. Thus glycogen breakdown appeared to be a major source of ongoing HGO. Over the last 60 minutes of the experimental period, the rate of glycogenolysis averaged 69 +/- 8 mumol/min/kg in saline-treated rats; this could account for about 80% of the total HGO. During both EC and HC studies, HGO was suppressed (5.5 +/- 3 and -3.6 +/- 10 mumol/min/kg, respectively; P < .001 for each). Net glycogen breakdown decreased by 50% in EC rats (P < .05) and ceased in HC rats (P < .001). Glycogen synthase was predominantly in the active form in all three experimental groups (87% +/- 2%, 89% +/- 2%, and 95% +/- 3% in saline, EC, and HC rats, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- Z Liu
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT
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Barrett EJ, Liu Z. Hepatic glucose metabolism and insulin resistance in NIDDM and obesity. BAILLIERE'S CLINICAL ENDOCRINOLOGY AND METABOLISM 1993; 7:875-901. [PMID: 8304916 DOI: 10.1016/s0950-351x(05)80238-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- E J Barrett
- University of Virginia Diabetes Center, Charlottesville 22908
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Katz H, Butler P, Homan M, Zerman A, Caumo A, Cobelli C, Rizza R. Hepatic and extrahepatic insulin action in humans: measurement in the absence of non-steady-state error. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 264:E561-6. [PMID: 8476034 DOI: 10.1152/ajpendo.1993.264.4.e561] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The isotope dilution technique has been extensively used to assess insulin action in humans. To determine if nonsteady state (NSS) has led to erroneous estimates of hepatic and extrahepatic insulin sensitivity, we measured glucose turnover in healthy subjects during infusion of insulin at rates of 0.25, 0.6, and 2.0 mU.kg-1.min-1. Turnover was calculated using Steele's traditional NSS equations [fixed-effective volume (pV) method] as well as with methods [radioactive infused glucose (hot-GINF) or variable pV] designed to minimize NSS error. In contrast to the fixed-pV method, both the hot-GINF and variable-pV methods indicated that several hours were required for suppression of hepatic glucose release at all insulin concentrations and that small increases in plasma insulin (approximately 100 pmol/l) had comparable effects on glucose disappearance and hepatic glucose release. Nevertheless, despite these differences, when turnover during the final hour of the insulin infusions was plotted vs. the prevailing insulin concentration, all three methods yielded similar insulin dose-response curves for suppression of hepatic glucose release. Thus despite previous errors in measurement of glucose turnover, the widely accepted belief that the human liver is exquisitely sensitive to small changes in insulin is correct.
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Affiliation(s)
- H Katz
- Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55905
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Misek D, Saltiel A. An inositol phosphate glycan derived from a Trypanosoma brucei glycosyl-phosphatidylinositol mimics some of the metabolic actions of insulin. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)41995-3] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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