Comparative gluconeogenesis in hepatocytes from salmonid fishes

Rates of gluconeogenic flux and substrate oxidation are assessed in isolated hepatocytes from three species of salmonid fishes: rainbow trout (Salmo gairdneri), coho salmon (Oncorhynchus kisutch), and sockeye salmon (Oncorhynchus nerka). Coho salmon displays the highest capacity for gluconeogenesis from lactate and alanine, but rates are well below those of eels. Enzyme compartmentation on isolated mitochondria shows that in trout and sockeye, phosphoenolpyruvate carboxykinase is almost entirely localized in the mitochondrion and the cytosol, respectively, while in the coho, 40% of phosphoenolpyruvate carboxykinase activity is associated with the cytosol. Freshly isolated salmonid hepatocytes are in negative glycogen balance. It is established here that at low (<250 μmol glucosyl units/g) glycogen concentrations a linear relationship exists between the rate of endogenous glucose production and the initial glycogen concentration. High rates of endogenous glycogen breakdown necessitate the use of radiotracers for determining gluconeogenic fluxes in fish hepatocytes. Rates of gluconeogenesis calculated from radiolabel experiments are compared with nonlabelled lactate and are determined not to be significantly different from each other. It is concluded that in fish hepatocytes, (i) radiotracer experiments give accurate estimates of gluconeogenesis, (ii) dilution of label at the oxalacetate level is insignificant, and, consequently, (iii) rates of 14CO2 production are a valid measure of true substrate oxidation.

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The impact of obesity, sex, and diet on hepatic glucose production in cats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.90771.2008 ◽

2009 ◽

Vol 296 (4) ◽

pp. R936-R943 ◽

Cited By ~ 28

Author(s):

Saskia Kley ◽

Margarethe Hoenig ◽

John Glushka ◽

Eunsook S. Jin ◽

Shawn C. Burgess ◽

...

Keyword(s):

Phosphoenolpyruvate Carboxykinase ◽

Citrate Synthase ◽

Hepatic Glucose Production ◽

Glucose Production ◽

Endogenous Glucose Production ◽

Hepatic Glucose Metabolism ◽

Peripheral Insulin Resistance ◽

Pyruvate Cycling ◽

Hepatic Glucose ◽

The Impact

Obesity is a risk factor for type 2 diabetes in cats. The risk of developing diabetes is severalfold greater for male cats than for females, even after having been neutered early in life. The purpose of this study was to investigate the role of different metabolic pathways in the regulation of endogenous glucose production (EGP) during the fasted state considering these risk factors. A triple tracer protocol using 2H2O, [U-13C3]propionate, and [3,4-13C2]glucose was applied in overnight-fasted cats (12 lean and 12 obese; equal sex distribution) fed three different diets. Compared with lean cats, obese cats had higher insulin ( P < 0.001) but similar blood glucose concentrations. EGP was lower in obese cats ( P < 0.001) due to lower glycogenolysis and gluconeogenesis (GNG; P < 0.03). Insulin, body mass index, and girth correlated negatively with EGP ( P < 0.003). Female obese cats had ∼1.5 times higher fluxes through phosphoenolpyruvate carboxykinase ( P < 0.02) and citrate synthase ( P < 0.05) than male obese cats. However, GNG was not higher because pyruvate cycling was increased 1.5-fold ( P < 0.03). These results support the notion that fasted obese cats have lower hepatic EGP compared with lean cats and are still capable of maintaining fasting euglycemia, despite the well-documented existence of peripheral insulin resistance in obese cats. Our data further suggest that sex-related differences exist in the regulation of hepatic glucose metabolism in obese cats, suggesting that pyruvate cycling acts as a controlling mechanism to modulate EGP. Increased pyruvate cycling could therefore be an important factor in modulating the diabetes risk in female cats.

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Gluconeogenesis is associated with high rates of tricarboxylic acid and pyruvate cycling in fasting northern elephant seals

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00042.2012 ◽

2012 ◽

Vol 303 (3) ◽

pp. R340-R352 ◽

Cited By ~ 13

Author(s):

Cory D. Champagne ◽

Dorian S. Houser ◽

Melinda A. Fowler ◽

Daniel P. Costa ◽

Daniel E. Crocker

Keyword(s):

Phosphoenolpyruvate Carboxykinase ◽

Glucose Production ◽

Tca Cycle ◽

Tricarboxylic Acid ◽

Endogenous Glucose Production ◽

Large Contribution ◽

Protein Loss ◽

Elephant Seals ◽

Pyruvate Cycling ◽

Northern Elephant Seals

Animals that endure prolonged periods of food deprivation preserve vital organ function by sparing protein from catabolism. Much of this protein sparing is achieved by reducing metabolic rate and suppressing gluconeogenesis while fasting. Northern elephant seals ( Mirounga angustirostris) endure prolonged fasts of up to 3 mo at multiple life stages. During these fasts, elephant seals maintain high levels of activity and energy expenditure associated with breeding, reproduction, lactation, and development while maintaining rates of glucose production typical of a postabsorptive mammal. Therefore, we investigated how fasting elephant seals meet the requirements of glucose-dependent tissues while suppressing protein catabolism by measuring the contribution of glycogenolysis, glycerol, and phosphoenolpyruvate (PEP) to endogenous glucose production (EGP) during their natural 2-mo postweaning fast. Additionally, pathway flux rates associated with the tricarboxylic acid (TCA) cycle were measured specifically, flux through phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate cycling. The rate of glucose production decreased during the fast (F1,13= 5.7, P = 0.04) but remained similar to that of postabsorptive mammals. The fractional contributions of glycogen, glycerol, and PEP did not change with fasting; PEP was the primary gluconeogenic precursor and accounted for ∼95% of EGP. This large contribution of PEP to glucose production occurred without substantial protein loss. Fluxes through the TCA cycle, PEPCK, and pyruvate cycling were higher than reported in other species and were the most energetically costly component of hepatic carbohydrate metabolism. The active pyruvate recycling fluxes detected in elephant seals may serve to rectify gluconeogeneic PEP production during restricted anaplerotic inflow in these fasting-adapted animals.

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TGF-β1/Smad3 Pathway Targets PP2A-AMPK-FoxO1 Signaling to Regulate Hepatic Gluconeogenesis

Journal of Biological Chemistry ◽

10.1074/jbc.m116.764910 ◽

2017 ◽

Vol 292 (8) ◽

pp. 3420-3432 ◽

Cited By ~ 36

Author(s):

Hariom Yadav ◽

Samir Devalaraja ◽

Stephanie T. Chung ◽

Sushil G. Rane

Keyword(s):

Glucose Homeostasis ◽

Phosphoenolpyruvate Carboxykinase ◽

Metabolic Diseases ◽

Nuclear Translocation ◽

Glucose Production ◽

Endogenous Glucose Production ◽

Prolonged Fasting ◽

Hepatic Gluconeogenesis ◽

Endogenous Glucose ◽

Tgf Β1

Maintenance of glucose homeostasis is essential for normal physiology. Deviation from normal glucose levels, in either direction, increases susceptibility to serious medical complications such as hypoglycemia and diabetes. Maintenance of glucose homeostasis is achieved via functional interactions among various organs: liver, skeletal muscle, adipose tissue, brain, and the endocrine pancreas. The liver is the primary site of endogenous glucose production, especially during states of prolonged fasting. However, enhanced gluconeogenesis is also a signature feature of type 2 diabetes (T2D). Thus, elucidating the signaling pathways that regulate hepatic gluconeogenesis would allow better insight into the process of normal endogenous glucose production as well as how this process is impaired in T2D. Here we demonstrate that the TGF-β1/Smad3 signaling pathway promotes hepatic gluconeogenesis, both upon prolonged fasting and during T2D. In contrast, genetic and pharmacological inhibition of TGF-β1/Smad3 signals suppressed endogenous glucose production. TGF-β1 and Smad3 signals achieved this effect via the targeting of key regulators of hepatic gluconeogenesis, protein phosphatase 2A (PP2A), AMP-activated protein kinase (AMPK), and FoxO1 proteins. Specifically, TGF-β1 signaling suppressed the LKB1-AMPK axis, thereby facilitating the nuclear translocation of FoxO1 and activation of key gluconeogenic genes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. These findings underscore an important role of TGF-β1/Smad3 signaling in hepatic gluconeogenesis, both in normal physiology and in the pathophysiology of metabolic diseases such as diabetes, and are thus of significant medical relevance.

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Changes in Glycogen and Lactate Levels in Migrating Salmonid Fishes Ascending Experimental "Endless" Fishways

Journal of the Fisheries Research Board of Canada ◽

10.1139/f64-022 ◽

1964 ◽

Vol 21 (2) ◽

pp. 255-290 ◽

Cited By ~ 22

Author(s):

Anne R. Connor ◽

Carl H. Elling ◽

Edgar C. Black ◽

Gerald B. Collins ◽

Joseph R. Gauley ◽

...

Keyword(s):

Muscle Glycogen ◽

Sockeye Salmon ◽

Oncorhynchus Tshawytscha ◽

Liver Glycogen ◽

Individual Performance ◽

Control Fish ◽

Salmo Gairdneri ◽

Upstream Migration ◽

Salmonid Fishes ◽

Muscle Lactate

Certain aspects of the performance and biochemistry of adult migrating salmonid fishes were investigated during ascents of 1:16- and 1:8-slope experimental fishways which employed locking devices permitting the simulation of fishways of any length. Fish tested were chinook salmon (Oncorhynchus tshawytscha), sockeye salmon (O. nerka) and steelhead trout (Salmo gairdneri) diverted from their upstream migration on the Columbia river at the Bonneville dam fishways during the summer of 1959. Blood and muscle lactate, and muscle and liver glycogen levels were determined in control fish, and in fish following three types of activity. Records of individual performance were kept.All species were willing to enter and capable of ascending fishways of either slope up to 1000 ft in height under favourable hydraulic conditions. Blood lactate and muscle glycogen determinations revealed the degree of exercise to be moderate even during prolonged ascents. Moderately high ascents (about 100 ft) in the steeper fishway apparently required the expenditure of some muscle glycogen whereas similar ascents in the 1:16 fishway did not. When muscle glycogen was utilized during prolonged ascents the expenditure appeared to be progressive. All species were apparently able to adapt to prolonged ascents of either fishway. Certain fish of each species tended to stop moving of their own volition in both fishways. After a 60-min volitional stop some evidence of recovery from the effects of exercise was observed. Discussion of the above data is presented.

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Relation of Water Temperature to Bacterial Kidney Disease in Coho Salmon (Oncorhynchus kisutch), Sockeye Salmon (O. nerka), and Steelhead Trout (Salmo gairdneri)

Journal of the Fisheries Research Board of Canada ◽

10.1139/f78-002 ◽

1978 ◽

Vol 35 (1) ◽

pp. 8-11 ◽

Cited By ~ 37

Author(s):

J. E. Sanders ◽

K. S. Pilcher ◽

J. L. Fryer

Keyword(s):

Kidney Disease ◽

Sockeye Salmon ◽

Coho Salmon ◽

Oncorhynchus Kisutch ◽

Salmo Gairdneri ◽

Causative Organism ◽

Steelhead Trout ◽

Bacterial Kidney Disease ◽

Percent Mortality ◽

Disease Agent

Juvenile coho salmon (Oncorhynchus kisutch), sockeye salmon (O. nerka), and steelhead trout (Salmo gairdneri) were infected by intraperitoneal injection of a suspension of the causative organism of bacterial kidney disease at seven experimental temperatures from 3.9 to 20.5 °C. In coho salmon and steelhead trout percent mortality was maximal (78–100%) in the range of 6.7–12.2 °C. As the temperature increased above 12.2 °C mortality declined progressively; at 20.5 °C it was only 8–14%. The two highest temperatures had some suppressing effect on the disease, which was greatest at 20.5 °C. In sockeye salmon this was not apparent, as percent mortality was essentially 100% at all temperatures from 6.7 to 20.5 °C; this species appeared to be highly susceptible to the disease agent. Temperature also influenced the mean number of days between infection and death. This interval was shortest in all three species of salmonids at the higher temperatures, varying from 21 to 34 days at 15.0–20.5 °C. It increased progressively as temperature decreased below this range; at 6.7 °C it varied from 60 to 71 days among the three species. Key words: bacterial kidney disease, temperature, salmonids, Corynebacterium, coho salmon, sockeye salmon, steelhead trout

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Protein Feeding Promotes Redistribution of Endogenous Glucose Production to the Kidney and Potentiates Its Suppression by Insulin

Endocrinology ◽

10.1210/en.2008-0601 ◽

2009 ◽

Vol 150 (2) ◽

pp. 616-624 ◽

Cited By ~ 48

Author(s):

Bruno Pillot ◽

Maud Soty ◽

Amandine Gautier-Stein ◽

Carine Zitoun ◽

Gilles Mithieux

Keyword(s):

Insulin Sensitivity ◽

Glucose Uptake ◽

Phosphoenolpyruvate Carboxykinase ◽

Glucose Production ◽

Glycogen Storage ◽

Endogenous Glucose Production ◽

Diabetic Patients ◽

Type 2 Diabetic Patients ◽

Protein Feeding ◽

Endogenous Glucose

The aim of this study was to assess in rats the effect of protein feeding on the: 1) distribution of endogenous glucose production (EGP) among gluconeogenic organs, and 2) repercussion on the insulin sensitivity of glucose metabolism. We used gene expression analyses, a combination of glucose tracer dilution and arteriovenous balance to quantify specific organ release, and hyperinsulinemic euglycemic clamps to assess EGP and glucose uptake. Protein feeding promoted a dramatic induction of the main regulatory gluconeogenic genes (glucose-6 phosphatase and phosphoenolpyruvate carboxykinase) in the kidney, but not in the liver. As a consequence, the kidney glucose release was markedly increased, compared with rats fed a normal starch diet. Protein feeding ameliorated the suppression of EGP by insulin and the sparing of glycogen storage in the liver but had no effect on glucose uptake. Combined with the previously reported induction of gluconeogenesis in the small intestine, the present work strongly suggests that a redistribution of glucose production among gluconeogenic organs might occur upon protein feeding. This phenomenon is in keeping with the improvement of insulin sensitivity of EGP, most likely involving the hepatic site. These data shed a new light on the improvement of glucose tolerance, previously observed upon increasing the amount of protein in the diet, in type 2 diabetic patients. Protein feeding increases kidney gluconeogenesis without increasing global endogenous glucose production, and improves insulin suppression of the latter, likely at the hepatic site.

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Involvement of liver and skeletal muscle in sucrose-induced insulin resistance: dose-response studies

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1994.266.5.r1637 ◽

1994 ◽

Vol 266 (5) ◽

pp. R1637-R1644 ◽

Cited By ~ 18

Author(s):

M. J. Pagliassotti ◽

K. A. Shahrokhi ◽

M. Moscarello

Keyword(s):

Insulin Resistance ◽

Skeletal Muscle ◽

Body Weight ◽

Dose Response ◽

Phosphoenolpyruvate Carboxykinase ◽

Glycogen Synthase ◽

Glucose Production ◽

Endogenous Glucose Production ◽

Male Rats ◽

Glycogen Accumulation

The ability of dietary sucrose to induce insulin resistance independent of changes in body weight is controversial. In the present study male rats were fed a high-starch (ST) diet (starch 68% of total kcal) ad libitum for 2 wk and then were fed equicalorically either the ST diet or a high-sucrose (SU) diet (sucrose 68% of total kcal) for 8 wk. Euglycemic, hyperinsulinemic (0, 1.2, 4.1, 8, 15 mU.kg-1.min-1, n = 6-8/group per dose) clamps were then used to establish dose-response relationships for glucose kinetics and metabolism. Body weight (513 +/- 3 g) and composition were similar between groups after the 8-wk dietary period. Glucose infusion rates (GIR; mg.kg-1.min-1) were significantly less in SU (0.9 +/- 5.8 +/- 0.6, 14.8 +/- 1.3, and 18 +/- 1.1) than in ST rats (4.1 +/- 0.9, 12.3 +/- 1.2, 22.6 +/- 1.5, and 25.9 +/- 1.8) at 1.2, 4.1, 8, and 15 mU.kg-1.min-1, respectively. Impaired suppression of endogenous glucose production accounted for 46, 43, 23, and 0% of the reduction in GIR in SU rats at 1.2, 4.1, 8, and 15 mU.kg-1.min-1, respectively. Despite basal hyperinsulinemia (38 +/- 2 microU/ml in SU vs. 26 +/- 2 microU/ml in ST rats), liver phosphoenolpyruvate carboxykinase (PEPCK) activity was 50% higher in SU than in ST rats and remained elevated in SU rats (by 30-40%) at the two lower insulin doses. No skeletal muscle glycogen accumulation occurred in SU rats at any of the insulin doses, and glycogen synthase I activity was significantly lower in SU rats at the two highest insulin doses.(ABSTRACT TRUNCATED AT 250 WORDS)

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