bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbohydrate ingestion can completely suppress endogenous glucose production during exercise
Authors: Jeukendrup Asker E. , Wagenmakers Anton J. M. , Stegen Jos H. C. H. , Gijsen Annemie P. , Brouns Fred , Saris Wim H. M.
Published: December 2017

The purposes of this study were 1) to investigate the effect of carbohydrate (CHO) ingestion on endogenous glucose production (EGP) during prolonged exercise, 2) to study whether glucose appearance in the circulation could be a limiting factor for exogenous CHO oxidation, and 3) to investigate whether large CHO feedings can reduce muscle glycogen oxidation during exercise. Six well-trained subjects exercised three times for 120 min at 50% maximum workload while ingesting water (FAST), a 4% glucose solution (LO-Glc), or a 22% glucose solution (HI-Glc). A primed continuous intravenous [6,6-2H2]glucose infusion was given, and the ingested glucose was enriched with [U-13C]glucose. Glucose ingestion significantly elevated CHO oxidation as well as the rates of appearance (Ra) and disappearance. Ra glucose equaled Ra of glucose in gut (Ra gut) during HI-Glc, whereas EGP was completely suppressed. During LO-Glc, EGP was partially suppressed, whereas Ra gut provided most of the total glucose Ra. We conclude that 1) high rates of CHO ingestion can completely block EGP, 2) Ra gut may be a limiting factor for exogenous CHO oxidation, and 3) muscle glycogen oxidation was not reduced by large glucose feedings.
Surgery-induced insulin resistance in human patients: relation to glucose transport and utilization
Authors: Thorell A. , Nygren J. , Hirshman M. F. , Hayashi T. , Nair K. S. , Horton E. S. , Goodyear L. J. , Ljungqvist O.
Published: December 2017

To investigate the underlying molecular mechanisms for surgery-induced insulin resistance in skeletal muscle, six otherwise healthy patients undergoing total hip replacement were studied before, during, and after surgery. Patients were studied under basal conditions and during physiological hyperinsulinemia (60 μU/ml). Biopsies of vastus lateralis muscle were used to measure GLUT-4 translocation, glucose transport, and glycogen synthase activities. Surgery reduced insulin-stimulated glucose disposal ( P < 0.05) without altering the insulin-stimulated increase in glucose oxidation or suppression of endogenous glucose production. Preoperatively, insulin infusion increased plasma membrane GLUT-4 in all six subjects ( P < 0.05), whereas insulin-stimulated GLUT-4 translocation only occurred in three patients postoperatively (not significant). Moreover, nonoxidative glucose disposal rates and basal levels of glycogen synthase activities in muscle were reduced postoperatively ( P< 0.05). These findings demonstrate that peripheral insulin resistance develops immediately postoperatively and that this condition might be associated with perturbations in insulin-stimulated GLUT-4 translocation as well as nonoxidative glucose disposal, presumably at the level of glycogen synthesis.
Hyperlactatemia reduces muscle glucose uptake and GLUT-4 mRNA while increasing (E1α)PDH gene expression in rat
Authors: Lombardi Anna M. , Fabris Roberto , Bassetto Flavia , Serra Roberto , Leturque Armelle , Federspil Giovanni , Girard Jean , Vettor Roberto
Published: December 2017

An increased basal plasma lactate concentration is present in many physiological and pathological conditions, including obesity and diabetes. We previously demonstrated that acute lactate infusion in rats produced a decrease in overall glucose uptake. The present study was carried out to further investigate the effect of lactate on glucose transport and utilization in skeletal muscle. In chronically catheterized rats, a 24-h sodium lactate or bicarbonate infusion was performed. To study glucose uptake in muscle, a bolus of 2-deoxy-[3H]glucose was injected in basal condition and during euglycemic-hyperinsulinemic clamp. Our results show that hyperlactatemia decreased glucose uptake in muscles (i.e., red quadriceps; P< 0.05). Moreover in red muscles, both GLUT-4 mRNA (−30% in red quadriceps and −60% in soleus; P < 0.025) and protein (−40% in red quadriceps; P < 0.05) were decreased, whereas the (E1α)pyruvate dehydrogenase (PDH) mRNA was increased (+40% in red quadriceps; P< 0.001) in lactate-infused animals. PDH protein was also increased (4-fold in red gastrocnemius and 2-fold in red quadriceps). These results indicate that chronic hyperlactatemia reduces glucose uptake by affecting the expression of genes involved in glucose metabolism in muscle, suggesting a role for lactate in the development of insulin resistance.
The acute-phase protein response to human immunodeficiency virus infection in human subjects
Authors: Jahoor Farook , Gazzard Brian , Phillips Gary , Sharpstone Danny , Delrosario Melanie , Frazer Margaret E. , Heird William , Smith Ruth , Jackson Alan
Published: December 2017

Although several studies have shown that asymptomatic human immunodeficiency virus infection elicits an increase in whole body protein turnover, it is not known whether this increased protein turnover includes changes in the kinetics of acute-phase proteins (APPs). To answer this question, we measured 1) the plasma concentrations of four positive (C-reactive protein, α1-antitrypsin, haptoglobin, and fibrinogen) and four negative APPs [albumin, high-density lipoprotein (HDL)-apolipoprotein (apo) A1, transthyretin, and retinol-binding protein] and 2) the fractional (FSR) and absolute (ASRs) synthesis rates of three positive and three negative APPs using a constant intravenous infusion of [2H5]phenylalanine in five subjects with symptom-free acquired immunodeficiency syndrome (AIDS) and five noninfected control subjects. Compared with the values of the controls, the plasma concentrations, FSRs, and ASRs of most positive APPs were higher in the AIDS group. The negative APPs had faster FSRs in the AIDS group, there was no difference between the ASRs of the two groups, and only HDL-apoA1 had a lower plasma concentration. These results suggest that symptom-free AIDS elicits an APP response that is different from bacterial infections, as the higher concentrations and faster rates of synthesis of the positive APPs are not accompanied by lower concentrations and slower rates of synthesis of most of the negative APPs.
Glutamine synthetase expression in muscle is regulated by transcriptional and posttranscriptional mechanisms
Authors: Labow Brian I. , Souba Wiley W. , Abcouwer Steve F.
Published: December 2017

Skeletal muscle exports glutamine (Gln) and increases the expression of the enzyme glutamine synthetase (GS) in response to physiological stress. Acute stress or direct glucocorticoid administration raises muscle GS mRNA levels dramatically without a parallel increase in GS protein levels. In the lung, this discrepancy is caused by feedback destabilization of the GS protein by its product Gln. It was hypothesized that muscle GS protein levels increase during stress only when the intracellular Gln pool has been depleted. Adult male rats were injected with the glucocorticoid hormone dexamethasone (DEX) to mimic the acute stress response and with the GS inhibitor methionine sulfoximine (MSO) to deplete muscle Gln stores. DEX increased GS mRNA levels by 2.8-fold but increased GS protein levels by an average of only 40%. MSO diminished muscle GLN levels by 68% and caused GS protein levels to rise in accordance with GS mRNA. Chronic stress was mimicked using 6 days of MSO treatment, which produced anorexia, 23% loss of body weight, and 64% decrease in muscle Gln levels, as well as pronounced increases in both muscle GS mRNA (26-fold) and protein levels (35-fold) without elevation of plasma glucocorticoid levels. Calorie-restricted pair-fed animals exhibited lesser increases in muscle GS mRNA (8-fold) and protein levels (5-fold) without a decline in muscle Gln content. Thus regulation of GS expression in both acute and chronic stress involved both transcriptional and posttranscriptional mechanisms, perhaps affected by muscle Gln content.
Hydration of fat-free body mass: new physiological modeling approach
Authors: Wang Zimian , Deurenberg Paul , Wang Wei , Pietrobelli Angelo , Baumgartner Richard N. , Heymsfield Steven B.
Published: December 2017

Water is an essential component of living organisms, and in adult mammals the fraction of fat-free body mass (FFM) as water is remarkably stable at ∼0.73. The stability of FFM hydration is a cornerstone of the widely used water isotope dilution method of estimating total body fat. At present, the only suggested means of studying FFM hydration is by experimental total body water (TBW) and FFM measurements. Although deviations from the classical hydration constant are recognized, it is unknown if these are explainable physiological aberrations and/or methodological errors. Moreover, many questions related to hydration stability prevail, including body mass and age effects. These unresolved questions and the importance of the TBW-fat estimation method led us to develop a cellular level FFM hydration model. This physiological model reveals that four water-related ratios combine to produce the observed TBW-to-FFM ratio. The mean and range of FFM hydration observed in adult humans can be understood with the proposed physiological model as can variation in the TBW-to-FFM ratio over the human life span. An extension of the model to the tissue-organ body composition level confirms on a theoretical basis a small but systematic decrease in hydration observed in mammals ranging in body mass by a factor of 105. The present study, the first to advance a physiological hydration model, provides a conceptual framework for the TBW-fat estimation method and identifies important areas that remain to be studied.
Glucose metabolism and β-cell mass in adult offspring of rats protein and/or energy restricted during the last week of pregnancy
Authors: Bertin Eric , Gangnerau Marie-Nöelle , Bailbé Danièle , Portha Bernard
Published: December 2017

An association between low birth weight and later impaired glucose tolerance was recently demonstrated in several human populations. Although fetal malnutrition is probably involved, the biological bases of such a relationship are not yet clear, and animal studies on the matter are scarce. The present study was aimed to identify, in adult (8-wk) female offspring, the effects of reduced protein and/or energy intake strictly limited to the last week of pregnancy. Thus we have tested three protocols of gestational malnutrition: a low-protein isocaloric diet (5 instead of 15%), with pair feeding to the mothers receiving the control diet; a restricted diet (50% of the control diet); and a low-protein restricted diet (50% of low-protein diet). Only the low-protein diet protocols, independent of total energy intake, led to a lower birth weight. The adult offspring female rats in the three deprived groups exhibited no decrease in body weight and no major impairment in glucose tolerance, glucose utilization, or glucose production (basal state and hyperinsulinemic clamp studies). However, pancreatic insulin content and β-cell mass were significantly decreased in the low-protein isocaloric diet group compared with the two energy-restricted groups. Such impairment of β-cell mass development induced by protein deficiency limited to the last part of intrauterine life could represent a situation predisposing to impaired glucose tolerance.
Insulin-like growth factor I in skeletal muscle after weight-lifting exercise in frail elders
Authors: Singh Maria A. Fiatarone , Ding Wenjing , Manfredi Thomas J. , Solares Guido S. , O’Neill Evelyn F. , Clements Karen M. , Ryan Nancy D. , Kehayias Joseph J. , Fielding Roger A. , Evans William J.
Published: December 2017

To assess muscle remodeling and functional adaptation to exercise and diet interventions, 26 men and women aged 72–98 yr underwent a vastus lateralis biopsy before and after placebo control condition, and progressive resistance training, multinutrient supplementation, or both. Type II atrophy, Z band, and myofibril damage were present at baseline. Combined weight lifting and nutritional supplementation increased strength by 257 ± 62% ( P = 0.0001) and type II fiber area by 10.1 ± 9.0% ( P = 0.033), with a similar trend for type I fiber area (+12.8 ± 22.2%). Exercise was associated with a 2.5-fold increase in neonatal myosin staining ( P = 0.0009) and an increase of 491 ± 137% ( P < 0.0001) in IGF-I staining. Ultrastructural damage increased by 141 ± 59% after exercise training ( P = 0.034). Strength increases were largest in those with the greatest increases in myosin, IGF-I, damage, and caloric intake during the trial. Age-related sarcopenia appears largely confined to type II muscle fibers. Frail elders respond robustly to resistance training with musculoskeletal remodeling, and significant increases in muscle area are possible with resistance training in combination with adequate energy intakes.
Substrate oxidation by the portal drained viscera of fed piglets
Authors: Stoll Barbara , Burrin Douglas G. , Henry Joseph , Yu Hung , Jahoor Farook , Reeds Peter J.
Published: December 2017

Fully fed piglets (28 days old, 7–8 kg) bearing portal, arterial, and gastric catheters and a portal flow probe were infused with enteral [U-13C]glutamate ( n = 4), enteral [U-13C]glucose ( n = 4), intravenous [U-13C]glucose ( n = 4), or intravenous [U-13C]glutamine ( n = 3). A total of 94% of the enteral [U-13C]glutamate but only 6% of the enteral [U-13C]glucose was utilized in first pass by the portal-drained viscera (PDV). The PDV extracted 6.5% of the arterial flux of [U-13C]glucose and 20.4% of the arterial flux of [U-13C]glutamine. The production of13CO2(percentage of dose) by the PDV from enteral glucose (3%), arterial glucose (27%), enteral glutamate (52%), and arterial glutamine (70%) varied widely. The substrates contributed 15% (enteral glucose), 19% (arterial glutamine), 29% (arterial glucose), and 36% (enteral glutamate) of the total production of CO2by the PDV. Enteral glucose accounted for 18% of the portal alanine and 31% of the portal lactate carbon outflow. We conclude that, in vivo, three-fourths of the energy needs of the PDV are satisfied by the oxidation of glucose, glutamate, and glutamine, and that dietary glutamate is the most important single contributor to mucosal oxidative energy generation.
Effects of dichloroacetate infusion on human skeletal muscle metabolism at the onset of exercise
Authors: Howlett Richard A. , Heigenhauser George J. F. , Hultman Eric , Hollidge-Horvat Melanie G. , Spriet Lawrence L.
Published: December 2017

This study investigated whether dichloroacetate (DCA) decreases the reliance on substrate level phosphorylation during the transition from rest to moderate-intensity exercise in humans. Nine subjects cycled at ∼65% of maximal oxygen uptake (V˙o2 max) after a saline or DCA (100 mg/kg body wt) infusion, with muscle biopsies taken at rest and at 30 s and 2 and 10 min of exercise. DCA infusion increased pyruvate dehydrogenase (PDH) activation at rest (4.0 ± 0.3 vs. 0.9 ± 0.1 mmol ⋅ kg wet wt−1⋅ min−1) and at 30 s (3.6 ± 0.2 vs. 2.5 ± 0.4 mmol ⋅ kg−1⋅ min−1) of exercise. As a result, acetyl-CoA (45.9 ± 5.9 vs. 11.3 ± 1.5 μmol/kg dry wt) and acetylcarnitine (13.1 ± 1.0 vs. 1.6 ± 0.3 mmol/kg dry wt) were markedly increased by DCA infusion at rest. These differences were maintained at 30 s and 2 min for both acetyl-CoA and acetylcarnitine. Resting muscle lactate and phosphocreatine (PCr) were not different between trials, but DCA infusion resulted in lower lactate accumulation throughout exercise, especially at 2 min (21.6 ± 3.1 vs. 44.6 ± 8.0 mmol/kg dry wt). PCr utilization in the initial 30 s (16.9 ± 0.4 vs. 31.7 ± 2.6 mmol/kg dry wt) and 2 min (27.8 ± 4.7 vs. 45.1 ± 2.6 mmol/kg dry wt) of exercise was decreased with DCA. This resulted in a lower accumulation of free inorganic phosphate at 30 s (25.4 ± 2.0 vs. 36.4 ± 2.8 mmol/kg dry wt) and 2 min (34.6 ± 4.7 vs. 50.5 ± 2.2 mmol/kg dry wt) with DCA and decreased glycogenolysis over 10 min. The data from this study support the hypothesis that increased provision of substrate by DCA infusion increases oxidative metabolism during the rest-to-work transition, resulting in decreased PCr utilization and an improved cellular energy state at the onset of exercise. The transitory improvement in energy state decreased glycogenolysis and lactate accumulation during moderate-intensity exercise.
Cytochromectranscriptional activation and mRNA stability during contractile activity in skeletal muscle
Authors: Freyssenet Damien , Connor Michael K. , Takahashi Mark , Hood David A.
Published: December 2017

We evaluated contractile activity-induced alterations in cytochrome c transcriptional activation and mRNA stability with unilateral chronic stimulation (10 Hz, 3 h/day) of the rat tibialis anterior (TA) muscle for 1, 2, 3, 4, 5, and 7 days ( n = 3–11/group). Transcriptional activation was assessed by direct plasmid DNA injection into the TA with a chloramphenicol acetyltransferase (CAT) reporter gene linked to 326 bp of the cytochrome c promoter. Cytochrome c mRNA in stimulated muscles increased by 1.3- to 1.7-fold above control between 1 and 7 days. Cytochrome c protein was increased after 5 days of stimulation to reach levels that were 1.9-fold higher than control by 7 days. Cytochrome c mRNA stability, determined with an in vitro decay assay, was greater in stimulated TA than in control between 2 and 4 days, likely mediated by the induction of a cytosolic factor. In contrast, cytochrome c transcriptional activation was elevated only after 5 days of stimulation when mRNA stability had returned to control levels. Thus the contractile activity-induced increase in cytochrome c mRNA was due to an early increase in mRNA stability, followed by an elevation in transcriptional activation, leading to an eventual increase in cytochrome c protein levels.
Changes in the circulating IGF system during short-term fasting and refeeding in rats
Authors: Frystyk J. , Delhanty P. J. D. , Skjærbæk C. , Baxter R. C.
Published: December 2017

There is little information on free insulin-like growth factor I (IGF-I) and its regulatory proteins during fasting and refeeding. Therefore, we examined rats during fasting (0, 1, 2, and 3 days) and refeeding (3, 6, and 12 h and 1, 2, 3, and 7 days) ( n = 6–9). Serum was analyzed for insulin, C-peptide, growth hormone (GH), free and total IGF-I, IGF-binding protein (IGFBP)-1 and -3, and the acid-labile subunit (ALS). Additionally, liver mRNA for IGF-I, IGFBP-1, and ALS was determined. Fasting reduced serum levels of GH, free and total IGF-I, IGFBP-3, and ALS, whereas IGFBP-1 was increased ( P < 0.0001). Refeeding normalized IGFBP-1 at 3 h and GH at 12 h. Free IGF-I changed in parallel with total IGF-I, ALS, and IGFBP-3, being normalized at 48 h of refeeding. IGFBP-1 (peptide and mRNA) correlated inversely with insulin and C-peptide ( P < 0.001). The correlation between peptide and mRNA was relatively strong for IGFBP-1 ( r 2 = 0.36; P < 0.0001), moderate for IGF-I ( r 2 = 0.18; P < 0.0005), and insignificant for ALS. In conclusion, insulin appears to regulate IGFBP-1 in fasted and refed rats. However, the normal inverse relationship between free IGF-I and IGFBP-1 was absent, and free IGF-I changed in parallel with total IGF-I and thus ALS and IGFBP-3. Finally, the regulation of the hepatic synthesis of IGF-I, IGFBP-1, and ALS seems to differ substantially.
Impact of 1 wk of diabetes on the regulation of myocardial carbohydrate and fatty acid oxidation
Authors: Chatham John C. , Gao Zhi-Ping , Forder John R.
Published: December 2017

The aim of this study was to investigate the effect of increasing exogenous palmitate concentration on carbohydrate and palmitate oxidation in hearts from control and 1-wk diabetic rats. Hearts were perfused with glucose, [3-13C]lactate, and [U-13C]palmitate. Substrate oxidation rates were determined by combining13C-NMR glutamate isotopomer analysis of tissue extracts with measurements of oxygen consumption. Carbohydrate oxidation was markedly depressed after diabetes in the presence of low (0.1 mM) but not high (1.0 mM) palmitate concentration. Increasing exogenous palmitate concentration 10-fold resulted in a 7-fold increase in the contribution of palmitate to energy production in controls but only a 30% increase in the diabetic group. Consequently, at 0.1 mM palmitate, the rate of fatty acid oxidation was higher in the diabetic group than in controls; however, at 1.0 mM fatty acid oxidation, it was significantly depressed. Therefore, after 1 wk of diabetes, the major differences in carbohydrate and fatty acid metabolism occur primarily at low rather than high exogenous palmitate concentration.
Minimal model SGoverestimation and SIunderestimation: improved accuracy by a Bayesian two-compartment model
Authors: Cobelli Claudio , Caumo Andrea , Omenetto Matteo
Published: December 2017

The intravenous glucose tolerance test (IVGTT) single-compartment minimal model (1CMM) method has recently been shown to overestimate glucose effectiveness and underestimate insulin sensitivity. Undermodeling, i.e., use of single- instead of two-compartment description of glucose kinetics, has been advocated to explain these limitations. We describe a new two-compartment minimal model (2CMM) into which we incorporate certain available knowledge on glucose kinetics. 2CMM is numerically identified using a Bayesian approach. Twenty-two standard IVGTT (0.30 g/kg) in normal humans were analyzed. In six subjects, the clamp-based index of insulin sensitivity ([Formula: see text]) was also measured. 2CMM glucose effectiveness ([Formula: see text]) and insulin sensitivity ([Formula: see text]) were, respectively, 60% lower ( P < 0.0001) and 35% higher ( P < 0.0001) than the corresponding 1CMM [Formula: see text] and[Formula: see text] indexes: 2.81 ± 0.29 (SE) vs.[Formula: see text] = 4.27 ± 0.33 ml ⋅ min−1 ⋅ kg−1and [Formula: see text] = 11.67 ± 1.71 vs.[Formula: see text] = 8.68 ± 1.62 102ml ⋅ min−1 ⋅ kg−1per μU/ml. [Formula: see text] was not different from[Formula: see text] = 12.61 ± 2.13 102ml ⋅ min−1 ⋅ kg−1per μU/ml (nonsignificant), whereas [Formula: see text]was 60% lower ( P < 0.02). In conclusion, a new 2CMM has been presented that improves the accuracy of glucose effectiveness and insulin sensitivity estimates of the classic 1CMM from a standard IVGTT in normal humans.
Comparison of techniques to estimate total body skeletal muscle mass in people of different age groups
Authors: Proctor D. N. , O’Brien P. C. , Atkinson E. J. , Nair K. S.
Published: December 2017

An estimate of total body muscle mass with dual-energy X-ray absorptiometry (DXA; appendicular muscle mass divided by 0.75) was compared with 24-h urinary creatinine excretion in 59 healthy men and women [20–30 yr (younger), 45–59 yr (middle age), and 60–79 yr (older)] who stayed in a clinical research center for 5 days. Total body water (2H2O dilution), fat (underwater weighing), bone mineral (DXA), and total body protein mass (based on a 4-compartment model) were also measured. Muscle mass estimates by DXA and creatinine were highly correlated ( r = 0.80). However, stepwise multiple regression indicated that a significant amount of additional between-subject variability in DXA-based muscle mass estimates could be explained by total body water. Creatinine excretion, knee extensor strength, and total body protein mass all decreased with age, suggesting a decline in muscle cell mass with aging. However, DXA-based muscle mass and measures of nonfat body mass (i.e., lean body mass by2H2O and fat-free body mass by underwater weighing) did not change with age. These results indicate that DXA and urinary creatinine excretion give different results regarding the decline in total body muscle mass with aging. The factor(s) responsible for the apparent underestimate of age-related sarcopenia by DXA remain to be fully defined, but changes in body water may be an important contributor.
Lipid rather than glucose metabolism is implicated in altered insulin secretion caused by oleate in INS-1 cells
Authors: Segall Laura , Lameloise Nathalie , Assimacopoulos-Jeannet Françoise , Roche Enrique , Corkey Pamela , Thumelin Stéphane , Corkey Barbara E. , Prentki Marc
Published: December 2017

A comprehensive metabolic study was carried out to understand how chronic exposure of pancreatic β-cells to fatty acids causes high basal secretion and impairs glucose-induced insulin release. INS-1 β-cells were exposed to 0.4 mM oleate for 3 days and subsequently incubated at 5 or 25 mM glucose, after which various parameters were measured. Chronic oleate promoted triglyceride deposition, increased fatty acid oxidation and esterification, and reduced malonyl-CoA at low glucose in association with elevated basal O2consumption and redox state. Oleate caused a modest (25%) reduction in glucose oxidation but did not affect glucose usage, the glucose 6-phosphate and citrate contents, and the activity of pyruvate dehydrogenase of INS-1 cells. Thus changes in glucose metabolism and a Randle-glucose/fatty acid cycle do not explain the altered secretory properties of β-cells exposed to fatty acids. The main response of INS-1 cells to chronic oleate, which is to increase the oxidation and esterification of fatty acids, may contribute to cause high basal insulin secretion via increased production of reducing equivalents and/or the generation of complex lipid messenger molecule(s).
Subcutaneous glucose predicts plasma glucose independent of insulin: implications for continuous monitoring
Authors: Rebrin Kerstin , Steil Garry M. , van Antwerp William P. , Mastrototaro John J.
Published: December 2017

The present study investigated the relationship between blood and subcutaneous interstitial fluid (ISF) glucose by employing an amperometric glucose sensor specifically developed for 3-day continuous glucose monitoring. The apparent sensor sensitivity and ISF glucose equilibration delay were estimated on separate days during hyperglycemic clamps in four dogs in which insulin was either suppressed with somatostatin, allowed to change, or increased with an exogenous infusion. A 2-h sensor “settling-in” period was allowed before the clamps. During insulin deficiency, the sensor sensitivity and ISF glucose delay were 0.23 ± 0.03 nA per mg/dl and 4.4 ± 0.8 min. Sensitivity was not affected by increases in endogenous (0.30 ± 0.04 vs. 0.28 ± 0.04 nA per mg/dl) or exogenous insulin (0.18 ± 0.01 vs. 0.16 ± 0.01 nA per mg/dl) nor was the delay (3.3 ± 1.2 vs. 5.7 ± 1.1 and 9.2 ± 2.6 vs. 12.3 ± 1.7 min; P > 0.05 for all). Sensor glucose accurately predicted plasma glucose without correcting for delays <10 min ( r > 0.9 for all), whereas for longer delays a digital corrective filter was used ( r = 0.91 with filter). We conclude that the relationship between blood and ISF glucose is not affected by insulin and that delays in ISF glucose equilibration can be corrected with digital filters.
Myocardial blood flow, oxygen consumption, and fatty acid uptake in endurance athletes during insulin stimulation
Authors: Takala Teemu O. , Nuutila Pirjo , Katoh Chietsugu , Luotolahti Matti , Bergman Jörgen , Mäki Maija , Oikonen Vesa , Ruotsalainen Ulla , Grönroos Tove , Haaparanta Merja , Kapanen Jukka , Knuuti Juhani
Published: December 2017

We have previously demonstrated reduced myocardial glucose uptake rates in hearts of endurance athletes, which could be due to increased use of alternative fuels or reduced energy demands. In the present study myocardial blood flow, oxygen consumption, and free fatty acid uptake were measured with [15O]H2O, [15O]O2, [18F]FTHA, and positron emission tomography (PET) in 9 endurance athletes and 11 sedentary men during euglycemic hyperinsulinemia. Compared with sedentary men, athletes had 33% lower myocardial blood flow, 27% lower oxygen consumption, and 20% lower estimated myocardial work per gram of tissue. Myocardial fatty acid uptake rates were not significantly different in endurance athletes (0.83 ± 0.29) and sedentary men (1.0 ± 0.31 μmol ⋅ 100 g−1 ⋅ min−1, P = 0.232). In conclusion, myocardial blood flow and oxygen consumption per unit mass of myocardium are reduced at rest in endurance athletes. This can be explained by reduced energy requirements per gram of tissue due to anatomic and physiological changes of the athlete’s heart.
Reduced β-cell function contributes to impaired glucose tolerance in dogs made obese by high-fat feeding
Authors: Kaiyala Karl J. , Prigeon Ronald L. , Kahn Steven E. , Woods Stephen C. , Porte Daniel , Schwartz Michael W.
Published: December 2017

The ability to increase β-cell function in the face of reduced insulin sensitivity is essential for normal glucose tolerance. Because high-fat feeding reduces both insulin sensitivity and glucose tolerance, we hypothesized that it also reduces β-cell compensation. To test this hypothesis, we used intravenous glucose tolerance testing with minimal model analysis to measure glucose tolerance ( K g), insulin sensitivity (SI), and the acute insulin response to glucose (AIRg) in nine dogs fed a chow diet and again after 7 wk of high-fat feeding. Additionally, we measured the effect of consuming each diet on 24-h profiles of insulin and glucose. After high-fat feeding, SI decreased by 57% ( P = 0.003) but AIRg was unchanged. This absence of β-cell compensation to insulin resistance contributed to a 41% reduction of K g( P = 0.003) and abolished the normal hyperbolic relationship between AIRg and SI observed at baseline. High-fat feeding also elicited a 44% lower 24-h insulin level ( P = 0.004) in association with an 8% reduction of glucose ( P = 0.0003). We conclude that high-fat feeding causes insulin resistance that is not compensated for by increased insulin secretion and that this contributes to the development of glucose intolerance. These effects of high-fat feeding may be especially deleterious to individuals predisposed to type 2 diabetes mellitus.
Increased intracellular localization of brain GLUT-1 transporter in response to ethanol during chick embryogenesis
Authors: Carver F. M. , Shibley I. A. , Miles D. S. , Pennington J. S. , Pennington S. N.
Published: December 2017

Fetal exposure to ethanol is associated with growth retardation of the developing central nervous system. We have previously described a chick model to study the molecular mechanism of ethanol effects on glucose metabolism in ovo. Total membrane fractions were prepared from day 4, day 5, and day 7 chick embryos exposed in ovo to ethanol or to vehicle. By Western blotting analysis, ethanol exposure caused a mean 7- to 10-fold increase in total GLUT-1 and a 2-fold increase in total GLUT-3. However, glucose uptake by ethanol-treated cells increased by only 10%. Analysis of isolated plasma (PM) and intracellular (IM) membranes from day 5 cranial tissue revealed a mean 25% decrease in GLUT-1 in the PM and a 66% increase in the IM in the ethanol group vs. control. The amount of PM GLUT-3 was unchanged but that of IM GLUT-3 was significantly decreased. The data suggest that GLUT-3 cell surface expression may be resistant to the suppressive effects of ethanol in the developing brain of ethanol-treated embryos. The overall increase in GLUT-1 may reflect a deregulation of the transporter induced by ethanol exposure. The increased IM localization and decreased amount of PM GLUT-1 may be a mechanism used by the ethanol-treated cell to maintain normal glucose uptake despite the overall increased level of the transporter.
Regulation of fatty acid oxidation of the heart by MCD and ACC during contractile stimulation
Authors: Goodwin Gary W. , Taegtmeyer Heinrich
Published: December 2017

We tested the hypothesis that the level of malonyl-CoA, as well as the corresponding rate of total fatty acid oxidation of the heart, is regulated by the opposing actions of acetyl-CoA carboxylase (ACC) and malonyl-CoA decarboxylase (MCD). We used isolated working rat hearts perfused under physiological conditions. MCD in heart homogenates was measured specifically by14CO2production from [3-14C]malonyl-CoA, and ACC was measured specifically based on the portion of total carboxylase that is citrate sensitive. Increased heart work (1 μM epinephrine + 40% increase in afterload) elicited a 40% increase in total β-oxidation of exogenous plus endogenous lipids, accompanied by a 33% decrease in malonyl-CoA. The basal activity and citrate sensitivity of ACC (reflecting its phosphorylation state) and citrate content were unchanged. AMP levels were also unchanged. MCD activity, when measured at a subsaturating concentration of malonyl-CoA (50 μM), was increased by 55%. We conclude that physiological increments in AMP during the work transition are insufficient to promote ACC phosphorylation by AMP-stimulated protein kinase. Rather, increased fatty acid oxidation results from increased malonyl-CoA degradation by MCD.
Chronic alcohol feeding impairs hepatic translation initiation by modulating eIF2 and eIF4E
Authors: Lang Charles H. , Wu Duanqing , Frost Robert A. , Jefferson Leonard S. , Vary Thomas C. , Kimball Scot R.
Published: December 2017

The present study examined potential cellular mechanisms responsible for the inhibition of protein synthesis in liver after chronic alcohol consumption. Rats were maintained on an alcohol-containing diet for 14 wk; control animals were fed isocalorically. Hepatic ATP content was not different in alcohol-fed and control animals. No alcohol-induced reduction in total hepatic RNA content (an estimate of ribosomal RNA) was detected, suggesting that alcohol decreased translational efficiency. Alcohol feeding increased the proportion of 40S and 60S ribosomal subunits in the nonpolysome-associated fraction by 30%. To identify mechanisms responsible for the impairment in initiation, several eukaryotic initiation factors (eIF) were analyzed. Alcohol feeding decreased hepatic eIF2B activity by 36%. This reduction was associated with a 20% decrease in eIF2Bε content and a 90% increase in eIF2α phosphorylation. Alcohol also dramatically influenced the distribution of eIF4E. Compared with pair-fed control values, alcohol feeding increased the amount of eIF4E present in the inactive 4E-binding protein 1 (4E-BP1) ⋅ eIF4E complex by 80% and decreased binding of eIF4G to eIF4E by 70%. However, the phosphorylation status of 4E-BP1 and eIF4E was not altered by alcohol. Although the plasma concentrations of threonine, proline, and citrulline were mildly decreased, the circulating amount of total amino acids was not altered by alcohol feeding. In summary, these data suggest that chronic alcohol consumption impairs translation initiation in liver by altering eIF2B activity as well as eIF4F function via changes in eIF4E availability.
Simultaneous indirect activity measurements of GH and PRL genes in the same, living mammosomatotrope
Authors: Willard Scott T. , Amstutz Michael D. , Abraham Elizabeth J. , Castaño Justo P. , Leaumont David C. , Faught William J. , Frawley L. Stephen
Published: December 2017

Dynamic intracellular processes in endocrine cells are usually controlled by the coordinated modulation of two or more functionally related genes. Attempts to gain a more complete understanding of these processes would be facilitated greatly by a method enabling activity measurements of two genes at the same time. Here we describe how we developed such a system and used it to determine indirectly whether individual, living pituitary cells could concurrently express both the growth hormone (GH) and prolactin (PRL) genes. Our results demonstrate that coexpression of these genes is indeed possible. Moreover, our findings provide a general paradigm for future “real-time” analysis of other interrelated genes involved in the regulation of endocrine processes.
Glucose-induced changes in protein kinase C and nitric oxide are prevented by vitamin E
Authors: Ganz Michael B. , Seftel Allen
Published: December 2017

Changes in activity or expression of protein kinase C (PKC), reactive oxygen products, and nitric oxide (NO) may account for the alteration in cell behavior seen in diabetes. These changes have been proposed to be part of the pathophysiology of erectile dysfunction. We sought to ascertain if corpus cavernosal vascular smooth muscle cells (CCSMC) grown in a high glucose milieu exhibit changes in the activity and expression of PKC isoforms, NO, and reactive oxygen products and to find out if these changes are prevented by α-tocopherol. Rat CCSMC were grown in 5, 15, and 30 mM glucose concentrations for 3, 7, and 14 days. PKC isoform expression was assayed with isoform-specific antibodies. In CCSMCs grown in 30 mM glucose for 2-wk, PKC-β2-isoform was upregulated ( n = 4; P < 0.01), whereas the expression of α-, δ-, ε-, and β1-isoforms was unchanged. NO as measured by nitrate-to-nitrite ratio was greatly diminished at 14 days in 30 mM ( n = 4; P < 0.002) compared with 5 mM glucose. Reactive oxygen products were upregulated at 14 days when they were assayed by the fluorescent probe dichlorofluorescein diacetate bis(acetoxy-methyl) (DCFH-DA) ( n= 5; P < 0.01). When these same cells were exposed to α-tocopherol for 14 days, there was a reduction of PKC-β2(57.8%; P < 0.01; n = 4) and a reduction in reactive oxygen product formation (71.1%; P < 0.001; n = 4), along with an increase in nitrate-to-nitrite ratio (43.9%; P < 0.01, n = 4). These results suggest that there may be an interrelationship between PKC, NO, and reactive oxygen product formation in CCSMC exposed to a high glucose environment.
Effect of carbohydrate ingestion on glycogen resynthesis in human liver and skeletal muscle, measured by 13C MRS
Authors: Casey Anna , Mann Rob , Banister Katie , Fox John , Morris Peter G. , Macdonald Ian A. , Greenhaff Paul L.
Published: December 2017

This study investigated the effect of carbohydrate (CHO) ingestion on postexercise glycogen resynthesis, measured simultaneously in liver and muscle ( n = 6) by 13C magnetic resonance spectroscopy, and subsequent exercise capacity ( n = 10). Subjects cycled at 70% maximal oxygen uptake for 83 ± 8 min on six separate occasions. At the end of exercise, subjects ingested 1 g/kg body mass (BM) glucose, sucrose, or placebo (control). Resynthesis of glycogen over a 4-h period after treatment ingestion was measured on the first three occasions, and subsequent exercise capacity was measured on occasions four through six. No glycogen was resynthesized during the control trial. Liver glycogen resynthesis was evident after glucose (13 ± 8 g) and sucrose (25 ± 5 g) ingestion, both of which were different from control ( P < 0.01). No significant differences in muscle glycogen resynthesis were found among trials. A relationship between the CHO load (g) and change in liver glycogen content (g) was evident after 30, 90, 150, and 210 min of recovery ( r = 0.59–0.79, P< 0.05). Furthermore, a modest relationship existed between change in liver glycogen content (g) and subsequent exercise capacity ( r= 0.53, P < 0.05). However, no significant difference in mean exercise time was found (control: 35 ± 5, glucose: 40 ± 5, and sucrose: 46 ± 6 min). Therefore, 1 g/kg BM glucose or sucrose is sufficient to initiate postexercise liver glycogen resynthesis, which contributes to subsequent exercise capacity, but not muscle glycogen resynthesis.
Overexpression of Bcl-xLin β-cells prevents cell death but impairs mitochondrial signal for insulin secretion
Authors: Zhou Yun-Ping , Pena John C. , Roe Michael W. , Mittal Anshu , Levisetti Matteo , Baldwin Aaron C. , Pugh William , Ostrega Diane , Ahmed Noreen , Bindokas Vytautas P. , Philipson Louis H. , Hanahan Douglas , Thompson Craig B. , Polonsky Kenneth S.
Published: December 2017

To study effects of Bcl-xLin the pancreatic β-cell, two transgenic lines were produced using different forms of the rat insulin promoter. Bcl-xLexpression in β-cells was increased 2- to 3-fold in founder (Fd) 1 and over 10-fold in Fd 2 compared with littermate controls. After exposure to thapsigargin (10 μM for 48 h), losses of cell viability in islets of Fd 1 and Fd 2 Bcl-xLtransgenic mice were significantly lower than in islets of wild-type mice. Unexpectedly, severe glucose intolerance was observed in Fd 2 but not Fd 1 Bcl-xLmice. Pancreatic insulin content and islet morphology were not different from control in either transgenic line. However, Fd 2 Bcl-xLislets had impaired insulin secretory and intracellular free Ca2+([Ca2+]i) responses to glucose and KCl. Furthermore, insulin and [Ca2+]iresponses to pyruvate methyl ester (PME) were similarly reduced as glucose in Fd 2 Bcl-xLislets. Consistent with a mitochondrial defect, glucose oxidation, but not glycolysis, was significantly lower in Fd 2 Bcl-xLislets than in wild-type islets. Glucose-, PME-, and α-ketoisocaproate-induced hyperpolarization of mitochondrial membrane potential, NAD(P)H, and ATP production were also significantly reduced in Fd 2 Bcl-xLislets. Thus, although Bcl-xLpromotes β-cell survival, high levels of expression of Bcl-xLresult in reduced glucose-induced insulin secretion and hyperglycemia due to a defect in mitochondrial nutrient metabolism and signaling for insulin secretion.
Methysergide reduces nonnutritive blood flow in normal and scalded skin
Authors: Zhang Xiao-Jun , Irtun Øivind , Zheng Yaoqing , Wolfe Robert R.
Published: December 2017

Methysergide is a serotonin antagonist and has been demonstrated to reduce wound blood flow and edema formation. We have determined the effect of methysergide on protein kinetics in normal and scalded skin of anesthetized rabbits.l-[ ring-13C6]- orl-[ ring-2H5]phenylalanine was used to reflect skin protein kinetics by use of an ear model, andl-[1-13C]leucine was used to reflect whole body protein kinetics. The results were that infusion of methysergide (2–3 mg ⋅ kg− 1 ⋅ h− 1) reduced the blood flow rate in normal skin by 50% without changing skin or whole body protein kinetics. After scald injury on the ear, administration of methysergide for 48 h reduced the weight of scalded ears (43 ± 4 vs. 30 ± 5 g, P < 0.01) and ear blood flow rate (42.6 ± 4.9 vs. 5.8 ± 1.0 ml ⋅ 100 g− 1 ⋅ min− 1, P < 0.0001) and did not change wound protein kinetics. Methysergide reduced arteriovenous shunting and maintained inward phenylalanine transport from the blood to the skin pool. Using the microsphere technique, we found that the infusion of methysergide decreased blood perfusion by 33–36% in both normal and scalded ear skin. We conclude that methysergide administration reduces nonnutritive, as opposed to nutritive, blood flow in normal and scalded skin.
Endurance exercise training attenuates leucine oxidation and BCOAD activation during exercise in humans
Authors: McKenzie Scott , Phillips Stuart M. , Carter Sherry L. , Lowther Stuart , Gibala Martin J. , Tarnopolsky Mark A.
Published: December 2017

We studied the effects of a 38-day endurance exercise training program on leucine turnover and substrate metabolism during a 90-min exercise bout at 60% peak O2consumption (V˙o2 peak) in 6 males and 6 females. Subjects were studied at both the same absolute (ABS) and relative (REL) exercise intensities posttraining. Training resulted in a significant increase in whole bodyV˙o2 peakand skeletal muscle citrate synthase (CS; P < 0.001), complex I-III ( P < 0.05), and total branched-chain 2-oxoacid dehydrogenase (BCOAD; P < 0.001) activities. Leucine oxidation increased during exercise for the pretraining trial (PRE, P < 0.001); however, there was no increase for either the ABS or REL posttraining trial. Leucine oxidation was significantly lower for females at all time points during rest and exercise ( P < 0.01). The percentage of BCOAD in the activated state was significantly increased after exercise for both the PRE and REL exercise trials, with the increase in PRE being greater ( P < 0.001) compared with REL ( P < 0.05). Females oxidized proportionately more lipid and less carbohydrate during exercise compared with males. In conclusion, we found that 38 days of endurance exercise training significantly attenuated both leucine oxidation and BCOAD activation during 90 min of endurance exercise at 60%V˙o2 peakfor both ABS and REL exercise intensities. Furthermore, females oxidize proportionately more lipid and less carbohydrate compared with males during endurance exercise.
Transgenic mice overexpressing GLUT-1 protein in muscle exhibit increased muscle glycogenesis after exercise
Authors: Ren Jian-Ming , Barucci Nicole , Marshall Bess A. , Hansen Polly , Mueckler Mike M. , Shulman Gerald I.
Published: December 2017

The purpose of the present study was to determine the rates of muscle glycogenolysis and glycogenesis during and after exercise in GLUT-1 transgenic mice and their age-matched littermates. Male transgenic mice (TG) expressing a high level of human GLUT-1 and their nontransgenic (NT) littermates underwent 3 h of swimming. Glycogen concentration was determined in gastrocnemius and extensor digitorum longus (EDL) muscles before exercise and at 0, 5, and 24 h postexercise, during which food (chow) and 10% glucose solution (as drinking water) were provided. Exercise resulted in ∼90% reduction in muscle glycogen in both NT (from 11.2 ± 1.4 to 2.1 ± 1.3 μmol/g) and TG (from 99.3 ± 4.7 to 11.8 ± 4.3 μmol/g) in gastrocnemius muscle. During recovery from exercise, the glycogen concentration increased to 38.2 ± 7.3 (5 h postexercise) and 40.5 ± 2.8 μmol/g (24 h postexercise) in NT mice. In TG mice, however, the increase in muscle glycogen concentration during recovery was greater (to 57.5 ± 7.4 and 152.1 ± 15.7 μmol/g at 5 and 24 h postexercise, respectively). Similar results were obtained from EDL muscle. The rate of 2-deoxyglucose uptake measured in isolated EDL muscles was 7- to 10-fold higher in TG mice at rest and at 0 and 5 h postexercise. There was no difference in muscle glycogen synthase activation measured in gastrocnemius muscles between NT and TG mice immediately after exercise. These results demonstrate that the rate of muscle glycogen accumulation postexercise exhibits two phases in TG: 1) an early phase (0–5 h), with rapid glycogen accumulation similar to that of NT mice, and 2) a progressive increase in muscle glycogen concentration, which differs from that of NT mice, during the second phase (5–24 h). Our data suggest that the high level of steady-state muscle glycogen in TG mice is due to the increase in muscle glucose transport activity.
Resistance exercise acutely increases MHC and mixed muscle protein synthesis rates in 78–84 and 23–32 yr olds
Authors: Hasten Debbie L. , Pak-Loduca Jina , Obert Kathleen A. , Yarasheski Kevin E.
Published: December 2017

We determined whether short-term weight-lifting exercise increases the synthesis rate of the major contractile proteins, myosin heavy chain (MHC), actin, and mixed muscle proteins in nonfrail elders and younger women and men. Fractional synthesis rates of mixed, MHC, and actin proteins were determined in seven healthy sedentary 23- to 32-yr-old and seven healthy 78- to 84-yr-old participants in paired studies done before and at the end of a 2-wk weight-lifting program. The in vivo rate of incorporation of 1-[13C]leucine into vastus lateralis MHC, actin, and mixed proteins was determined using a 14-h constant intravenous infusion of 1-[13C]leucine. Before exercise, the mixed and MHC fractional synthetic rates were lower in the older than in the younger participants ( P ≤ 0.04). Baseline actin protein synthesis rates were similar in the two groups ( P = not significant). Over a 2-wk period, participants completed ten 1- to 1.5-h weight-lifting exercise sessions: 2–3 sets per day of 9 exercises, 8–12 repetitions per set, at 60–90% of maximum voluntary muscle strength. At the end of exercise, MHC and mixed protein synthetic rates increased in the younger (88 and 121%) and older participants (105 and 182%; P < 0.001 vs. baseline). These findings indicate that MHC and mixed protein synthesis rates are reduced more than actin in advanced age. Similar to that of 23–32 yr olds, the vastus lateralis muscle in 78–84 yr olds retains the capacity to increase MHC and mixed protein synthesis rates in response to short-term resistance exercise.