bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid phase advance of the 24-h melatonin profile in response to afternoon dark exposure
Authors: Van Cauter Eve , Moreno-Reyes Rodrigo , Akseki Elif , L’Hermite-Balériaux Mireille , Hirschfeld Ulrich , Leproult Rachel , Copinschi Georges
Published: December 2017

To investigate the adaptation of melatonin secretion to an abrupt time shift and the effects of sleep facilitation with a hypnotic, eight subjects were submitted to an 8-h advance shift achieved by advancing bedtimes from 2300–0700 to 1500–2300. Each subject participated in two studies (i.e., placebo and zolpidem). Each study included a baseline period with dim light during waking hours and 2300–0700 bedtimes in total darkness. Blood samples for determination of plasma melatonin were obtained at 20-min intervals for 68 h. Advanced exposure to sleep and darkness resulted in a nearly 2-h advance of melatonin onset, which appeared within 6 h after lights-out during the first shifted night, and an almost 1-h advance of the melatonin offset. No further adaptation occurred during the second shifted sleep period. Zolpidem had no beneficial effects on the adaptation of the melatonin profile. There was no relationship between sleep parameters and the magnitude of the melatonin shifts. Thus the overall advance of melatonin profiles was primarily achieved during the initial exposure to an 8-h period of darkness. The present data suggest that exposure to dark affects human circadian phase.
Regulation of extracellular calcium-activated cation currents by cAMP in parathyroid cells
Authors: Chang Wenhan , Chen Tsui-Hua , Pratt Stacy , Shoback Dolores
Published: December 2017

Parathyroid cells express Ca2+-sensing receptors that couple changes in the extracellular Ca2+concentration ([Ca2+]o) to increases in the intracellular free Ca2+concentration ([Ca2+]i) and to the suppression of parathyroid hormone secretion. Using whole cell patch clamping, we previously identified voltage-independent Ca2+-conducting currents in bovine parathyroid cells that increased with rising [Ca2+]oand were blocked by Cd2+and nifedipine. Because cAMP-dependent phosphorylation regulates dihydropyridine-sensitive Ca2+channels in other systems, we tested whether cAMP modulates these currents. At 0.7 mM Ca2+, nonselective Ca2+-conducting currents were suppressed by 30–50% when the recording pipette was perfused with cAMP. High-[Ca2+]o-induced increases in membrane currents were also abrogated. The effects of cAMP were reversible and dose dependent (3 × 10−9to 3 × 10−3M) and required ATP in the pipette solution. Perfusion of the cell interior with the catalytic subunit of protein kinase A mimicked the effects of cAMP, as did perfusion of the bath with the adenylate cyclase activator forskolin. These findings support the idea that cAMP-dependent phosphorylation suppresses high-[Ca2+]o-induced cation currents and may play a role in regulating ion fluxes in parathyroid cells.
Effect of the shift of the sleep-wake cycle on three robust endocrine markers of the circadian clock
Authors: Goichot Bernard , Weibel Laurence , Chapotot Florian , Gronfier Claude , Piquard François , Brandenberger Gabrielle
Published: December 2017

To determine the effect of a phase shift in sleep on the circadian clock, thyroid-stimulating hormone (TSH), cortisol, and melatonin, three robust markers of the circadian clock, were analyzed using a 10-min blood sampling procedure. In an initial experiment eight subjects were studied during two experimental sessions: once under baseline conditions with normal nighttime sleep from 2300 to 0700 (baseline) and once after a night of sleep deprivation followed by daytime sleep from 0700 to 1500 ( day 1). In a second experiment, carried out on seven subjects, the 24-h hormone profiles of the first day ( day 1) were compared with those of the second day ( day 2) of the sleep shift. During the night of sleep deprivation ( day 1) the TSH surge was higher than during baseline conditions, whereas melatonin and cortisol rhythms remained unaffected. On day 2 the amplitude of the nocturnal TSH surge was reduced in comparison to day 1, whereas the amplitudes of melatonin and cortisol rhythms were unchanged. There was a clear phase shift in the three endocrine rhythms. Triiodothyronine levels were slightly higher in the morning after the first night of sleep deprivation. These results demonstrate that 2 consecutive days of sleep shift are sufficient to affect the timing of the commonly accepted circadian markers, suggesting the existence of a rapid resetting effect on the circadian clock. TSH reacts in a distinctive manner to the sleep-wake cycle manipulation by modulating the amplitude of the nocturnal surge. This amplitude modulation is probably an integral part of the phase-shifting mechanisms controlled by the circadian clock.
Differential regulation of arginases and inducible nitric oxide synthase in murine macrophage cells
Authors: Morris Sidney M. , Kepka-Lenhart Diane , Chen Li-Chun
Published: December 2017

Activated macrophages avidly consume arginine via the action of inducible nitric oxide synthase (iNOS) and/or arginase. In contrast to our knowledge regarding macrophage iNOS expression, the stimuli and mechanisms that regulate expression of the cytosolic type I (arginase I) or mitochondrial type II (arginase II) isoforms of arginase in macrophages are poorly defined. We show that one or both arginase isoforms may be induced in the RAW 264.7 murine macrophage cell line and that arginase expression is regulated independently of iNOS expression. For example, 8-bromo-cAMP strongly induced both arginase I and II mRNAs but not iNOS. Whereas interferon-γ induced iNOS but not arginase, 8-bromo-cAMP and interferon-γ mutually antagonized induction of iNOS and arginase I mRNAs. Dexamethasone, which did not induce either arginase or iNOS, almost completely abolished induction of arginase I mRNA by 8-bromo-cAMP but enhanced induction of arginase II mRNA. Lipopolysaccharide (LPS) induced arginase II mRNA, but 8-bromo-cAMP plus LPS resulted in synergistic induction of both arginase I and II mRNAs. In all cases, increases in arginase mRNAs were sufficient to account for the increases in arginase activity. These complex patterns of expression suggest that the arginase isoforms may play distinct, although partially overlapping, functional roles in macrophage arginine metabolism.
Corticosteroid-independent inhibition of tumor necrosis factor production by the neuropeptide urocortin
Authors: Agnello Davide , Bertini Riccardo , Sacco Silvano , Meazza Cristina , Villa Pia , Ghezzi Pietro
Published: December 2017

Urocortin (UCN) is a neuropeptide homologous with corticotropin-releasing factor (CRF), which has anti-inflammatory activities not all mediated by corticosteroids. In mice, UCN (1 μg/mouse sc) significantly reduced lipopolysaccharide (LPS)-induced serum tumor necrosis factor (TNF) and interleukin (IL)-1β levels in vivo but did not affect serum IL-6. These effects were paralleled by a rise in corticosterone (CS) levels. Blockade of the CS increase by cyanoketone did not prevent TNF inhibition by UCN, suggesting the neuropeptide has anti-inflammatory mechanisms independent of the hypothalamus-pituitary-adrenal axis. In fact UCN had a direct inhibitory effect on LPS-induced TNF in rat Kupffer cells at concentrations between 10−10and 10−16M, and this effect was related to increased cAMP levels. However, the in vivo inhibition of LPS-induced IL-1β by UCN was reversed by cyanoketone, indicating that the increase of endogenous glucocorticoids might be more important in IL-1β inhibition than in TNF inhibition by UCN.
Forearm norepinephrine spillover during standing, hyperinsulinemia, and hypoglycemia
Authors: Paramore Deanna S. , Fanelli Carmine G. , Shah Suresh D. , Cryer Philip E.
Published: December 2017

Plasma norepinephrine (NE) concentrations are a fallible index of sympathetic neural activity because circulating NE can be derived from sympathetic nerves, the adrenal medullas, or both and because of regional differences in sympathetic neural activity. We used isotope dilution measurements of systemic and forearm NE spillover rates (SNESO and FNESO, respectively) to study the sympathochromaffin system during prolonged standing, hyperinsulinemic euglycemia, and hyperinsulinemic hypoglycemia in healthy humans. Prolonged standing led to decrements in blood pressure without increments in heart rate, the pattern of incipient vasodepressor syncope. FNESO was not increased (0.58 ± 0.20 to 0.50 ± 0.21 pmol ⋅ min−1⋅ 100 ml tissue−1), suggesting that the approximately twofold increments in plasma NE and SNESO were derived from sympathetic nerves other than those in the forearm (with a possible contribution from the adrenal medullas). Hyperinsulinemia per se (euglycemia maintained) stimulated sympathetic neural activity, as evidenced by increments in FNESO (0.57 ± 0.11 to 1.25 ± 0.25 pmol ⋅ min−1⋅ 100 ml tissue−1, P < 0.05), but not adrenomedullary activity. Hypoglycemia per se stimulated adrenomedullary activity (plasma epinephrine from 190 ± 70 to 1720 ± 320, pmol/l, P < 0.01). Although SNESO ( P < 0.05) and perhaps plasma NE ( P < 0.06) were raised to a greater extent during hyperinsulinemic hypoglycemia than during hyperinsulinemic euglycemia, FNESO was not. Thus these data do not provide direct support for the concept that hypoglycemia per se also stimulates sympathetic neural activity.
Role of local contractile activity and muscle fiber type on LPL regulation during exercise
Authors: Hamilton Marc T. , Etienne Jacqueline , McClure Warren C. , Pavey Brian S. , Holloway Alisha K.
Published: December 2017

The purpose of this study was to determine the influence of local contractile activity on lipoprotein lipase (LPL) regulation in skeletal muscle. Short-term voluntary run training increased LPL mRNA concentration and LPL immunoreactive mass about threefold in white skeletal muscles of the rat hindlimb (all P < 0.01). Training also increased total and heparin-releasable LPL enzyme activity in white hindlimb muscles and in postheparin plasma ( P< 0.05). Training did not enhance LPL regulation in a white muscle that was not recruited during running (masseter). LPL levels were already high in red skeletal muscles of control rats, and training did not result in a further rise. In resting rats, local electrical stimulation of a motor nerve to a predominantly white muscle caused a significant rise in LPL mRNA, immunoreactive mass, and enzyme activity relative to the contralateral control muscle of the same animals (all P < 0.01). Finally, LPL expression was several times greater in a red muscle (soleus) of rats with normal postural activity than rats with immobilized hindlimbs ( P < 0.01). In summary, these studies support the hypothesis that local contractile activity is required for increasing LPL expression during exercise training and for maintaining a high level of LPL expression in postural muscles.
Malonyl-CoA, fuel sensing, and insulin resistance
Authors: Ruderman Neil B. , Saha Asish K. , Vavvas Demetrios , Witters Lee A.
Published: December 2017

Malonyl-CoA is an allosteric inhibitor of carnitine palmitoyltransferase (CPT) I, the enzyme that controls the transfer of long-chain fatty acyl (LCFA)-CoAs into the mitochondria where they are oxidized. In rat skeletal muscle, the formation of malonyl-CoA is regulated acutely (in minutes) by changes in the activity of the β-isoform of acetyl-CoA carboxylase (ACCβ). This can occur by at least two mechanisms: one involving cytosolic citrate, an allosteric activator of ACCβand a precursor of its substrate cytosolic acetyl-CoA, and the other involving changes in ACCβphosphorylation. Increases in cytosolic citrate leading to an increase in the concentration of malonyl-CoA occur when muscle is presented with insulin and glucose, or when it is made inactive by denervation, in keeping with a diminished need for fatty acid oxidation in these situations. Conversely, during exercise, when the need of the muscle cell for fatty acid oxidation is increased, decreases in the ATP/AMP and/or creatine phosphate-to-creatine ratios activate an isoform of an AMP-activated protein kinase (AMPK), which phosphorylates ACCβand inhibits both its basal activity and activation by citrate. The central role of cytosolic citrate links this malonyl-CoA regulatory mechanism to the glucose-fatty acid cycle concept of Randle et al. (P. J. Randle, P. B. Garland. C. N. Hales, and E. A. Newsholme. Lancet 1: 785–789, 1963) and to a mechanism by which glucose might autoregulate its own use. A similar citrate-mediated malonyl-CoA regulatory mechanism appears to exist in other tissues, including the pancreatic β-cell, the heart, and probably the central nervous system. It is our hypothesis that by altering the cytosolic concentrations of LCFA-CoA and diacylglycerol, and secondarily the activity of one or more protein kinase C isoforms, changes in malonyl-CoA provide a link between fuel metabolism and signal transduction in these cells. It is also our hypothesis that dysregulation of the malonyl-CoA regulatory mechanism, if it leads to sustained increases in the concentrations of malonyl-CoA and cytosolic LCFA-CoA, could play a key role in the pathogenesis of insulin resistance in muscle. That it may contribute to abnormalities associated with the insulin resistance syndrome in other tissues and the development of obesity has also been suggested. Studies are clearly needed to test these hypotheses and to explore the notion that exercise and some pharmacological agents that increase insulin sensitivity act via effects on malonyl-CoA and/or cytosolic LCFA-CoA.
Early biochemical events in insulin-stimulated fluid phase endocytosis
Authors: Pitterle Diana M. , Sperling Robert T. , Myers Martin G. , White Morris F. , Blackshear Perry J.
Published: December 2017

We examined the initial molecular mechanisms by which cells nonselectively internalize extracellular solutes in response to insulin. Insulin-stimulated fluid phase endocytosis (FPE) was examined in responsive cells, and the roles of the insulin receptor, insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3′-kinase (PI 3′-kinase), Ras, and mitogen-activated protein kinase kinase (MEK) were assessed. Active insulin receptors were essential, as demonstrated by the stimulation of FPE by insulin in HIRc-B cells (Rat-1 cells expressing 1.2 × 106normal insulin receptors/cell) but not in untransfected Rat-1 cells or in Rat-1 cells expressing the inactive A/K1018 receptor. IRS-1 expression augmented insulin-stimulated FPE, as assessed in 32D cells, a hematopoietic precursor cell line lacking endogenous IRS-1. Insulin-stimulated FPE was inhibited in mouse brown adipose tissue (BAT) cells expressing the 17N dominant negative mutant Ras and was augmented in cells expressing wild-type Ras. The MEK inhibitor PD-98059 had little effect on insulin-stimulated FPE in BAT cells. In 32D cells, but not in HIRc-B and BAT cells, insulin-stimulated FPE was inhibited by 10 nM wortmannin, an inhibitor of PI 3′-kinase. The results indicate that the insulin receptor, IRS-1, Ras, and, perhaps in certain cell types, PI 3′-kinase are involved in mediating insulin-stimulated FPE.
Effect of high-intensity exercise training on lactate/H+ transport capacity in human skeletal muscle
Authors: Pilegaard Henriette , Domino Kristian , Noland Thomas , Juel Carsten , Hellsten Ylva , Halestrap Andrew P. , Bangsbo Jens
Published: December 2017

The present study examined the effect of high-intensity exercise training on muscle sarcolemmal lactate/H+ transport and the monocarboxylate transporters (MCT1 and MCT4) as well as lactate and H+ release during intense exercise in humans. One-legged knee-extensor exercise training was performed for 8 wk, and biopsies were obtained from untrained and trained vastus lateralis muscle. The rate of lactate/H+ transport determined in sarcolemmal giant vesicles was 12% higher ( P < 0.05) in the trained than in untrained muscle ( n = 7). The content of MCT1 and MCT4 protein was also higher (76 and 32%, respectively; n = 4) in trained muscle. Release of lactate and H+ from the quadriceps muscle at the end of intense exhaustive knee-extensor exercise was similar in the trained and untrained leg, although the estimated muscle intracellular-to-interstitial gradients of lactate and H+ were lower ( P < 0.05) in the trained than in the untrained muscle. The present data show that intense exercise training can increase lactate/H+transport capacity in human skeletal muscle as well as improve the ability of the muscle to release lactate and H+ during contractions.
Oxytocin increases the [Ca2+]isensitivity of human myometrium during the falling phase of phasic contractions
Authors: McKillen Keena , Thornton Steven , Taylor Colin W.
Published: December 2017

Oxytocin is commonly used to induce or augment labor, but its mode of action is uncertain. To address the issue, isometric tension and the intracellular free Ca2+ concentration ([Ca2+]i) were simultaneously recorded from isolated strips of pregnant human myometrium loaded with fura 2. The changes in [Ca2+]iand tension during phasic contractions were indistinguishable in myometrium taken before or after the onset of labor, enabling samples to be pooled. Oxytocin (10 nM) had no effect on basal [Ca2+]ior tension, but it increased both the [Ca2+]iand the tension recorded during phasic contractions. Analysis of the [Ca2+]i-tension relationship revealed that during the falling (relaxation) phase of the contractile response, oxytocin increased the tension recorded at each [Ca2+]i. By manipulating extracellular Ca2+during phasic contractions, it was possible to ensure that the [Ca2+]isignals were similar in the presence and absence of oxytocin, yet oxytocin still improved the [Ca2+]i-tension relationship. We conclude that 10 nM oxytocin increases the [Ca2+]isensitivity of the contractile proteins only after a contraction has begun, possibly by causing inhibition of myosin light chain phosphatase.
Whole body glucose metabolism
Authors: Zierler Kenneth
Published: December 2017

This review describes major factors that, singly or together, influence the concentration and distribution ofd-glucose in mammals, particularly in humans, with emphasis on rest, physical activity, and alimentation. It identifies areas of uncertainty: distribution and concentrations of glucose in interstitial fluid, kinetics and mechanism of transcapillary glucose transport, kinetics and mechanism of glucose transport via its transporters into cells, detailed mechanisms by which hormones, exercise, and hypoxia affect glucose movement across cell membranes, whether translocation of glucose transporters to the cell membrane accounts completely, or even mainly, for insulin-stimulated glucose uptake, whether exercise stimulates release of a circulating insulinomimetic factor, and the relation between muscle glucose uptake and muscle blood flow. The review points out that there is no compartment of glucose in the body at which all glucose is at the same concentration, and that models of glucose metabolism, including effects of insulin on glucose metabolism based on assumptions of concentration homogeneity, cannot be entirely correct. A fresh approach to modeling is needed.
Effect of leptin deficiency on metabolic rate inob/obmice
Authors: Breslow Michael J. , Min-Lee Kyoung , Brown Daniel R. , Chacko V. P. , Palmer David , Berkowitz Dan E.
Published: December 2017

Reduced metabolic rate may contribute to weight gain in leptin-deficient ( ob/ob) mice; however, available studies have been criticized for referencing O2 consumption (V˙o 2) to estimated rather than true lean body mass. To evaluate whether leptin deficiency reduces energy expenditure, four separate experiments were performed: 1) NMR spectroscopy was used to measure fat and nonfat mass, permittingV˙o 2 to be referenced to true nonfat mass; 2) dietary manipulation was used in an attempt to eliminate differences in body weight and composition between ob/ob and C57BL/6J mice; 3) short-term effects of exogenous leptin (0.3 mg ⋅ kg−1 ⋅ day−1) on V˙o 2 were examined; and 4) body weight and composition were compared in leptin-repleted and pair-fed ob/ob animals. ob/ob animals had greater mass, less lean body mass, and a 10% higher metabolic rate whenV˙o 2 was referenced to lean mass. Dietary manipulation achieved identical body weight in ob/ob and C57BL/6J animals; however, despite weight gain in C57BL/6J animals, percent fat mass remained higher in ob/ob animals (55 vs. 30%). Exogenous leptin increasedV˙o 2 in ob/ob but not control animals. Weight loss in leptin-repleted ob/ob mice was greater than in pair-fed animals (45 vs. 17%). We conclude, on the basis of the observed increase inV˙o 2 and accelerated weight loss seen with leptin repletion, that leptin deficiency causes a reduction in metabolic rate in ob/obmice. In contrast, these physiological studies suggest that comparison of V˙o 2 in obese and lean animals does not produce useful information on the contribution of leptin to metabolism.
Voltage-dependent entry and generation of slow Ca2+oscillations in glucose-stimulated pancreatic β-cells
Authors: Dryselius Staffan , Grapengiesser Eva , Hellman Bo , Gylfe Erik
Published: December 2017

The role of voltage-dependent Ca2+entry for glucose generation of slow oscillations of the cytoplasmic Ca2+concentration ([Ca2+]i) was evaluated in individual mouse pancreatic β-cells. Like depolarization with K+, a rise of the glucose concentration resulted in an enhanced influx of Mn2+, which was inhibited by nifedipine. This antagonist of L-type Ca2+channels also blocked the slow oscillations of [Ca2+]iinduced by glucose. The slow oscillations occurred in synchrony with variations in Mn2+influx and bursts of action currents, with the elevation of [Ca2+]ibeing proportional to the frequency of the action currents. A similar relationship was obtained when Ca2+was replaced with Sr2+. Occasionally, the slow [Ca2+]ioscillations were superimposed with pronounced spikes temporarily arresting the action currents. It is concluded that the glucose-induced slow oscillations of [Ca2+]iare caused by periodic depolarization with Ca2+influx through L-type channels. Ca2+spiking, due to intracellular mobilization, may be important for chopping the slow oscillations of [Ca2+]iinto shorter ones characterizing β-cells situated in pancreatic islets.
Kinetic profile of overall elimination of 5-methyltetrahydropteroylglutamate in rats
Authors: Han Yong-Hae , Kato Yukio , Kusuhara Hiroyuki , Suzuki Hiroshi , Shimoda Minoru , Kokue Eiichi , Sugiyama Yuichi
Published: December 2017

The in vivo biliary and urinary excretion kinetics of 5-methyltetrahydropteroylglutamate (5-CH3-H4PteGlu) were studied in rats. During infusion at various rates (48–965 nmol ⋅ h−1⋅ kg−1), the total body clearance (CLtotal) of 5-CH3-H4PteGlu could be attributed almost entirely to the sum of the biliary and urinary (CLurine,p) excretion clearances. After a 4-h infusion at the highest rate, the 5-CH3-H4PteGlu in the liver was 10 times higher than the endogenous level, whereas its polyglutamate form did not increase, suggesting that most of the infused 5-CH3-H4PteGlu is not incorporated in the polyglutamate pool but is eliminated by excretion. The parallel increase in CLtotaland CLurine,pwith the increase in infusion rate might result from saturation of reabsorption at the renal proximal tubules, since the urinary excretion clearance, defined with respect to the kidney concentration, also increased while the biliary excretion clearance, defined with respect to the liver concentration, remained almost constant. We conclude that the hepatobiliary excretion is a relatively low-affinity process with a constant clearance, whereas the renal tubular reabsorption is saturated at higher plasma 5-CH3-H4PteGlu concentration (∼0.5 μM). Urinary excretion becomes the predominant elimination route for any excess 5-CH3-H4PteGlu in the body.
Postexercise net protein synthesis in human muscle from orally administered amino acids
Authors: Tipton Kevin D. , Ferrando Arny A. , Phillips Stuart M. , Doyle David , Wolfe Robert R.
Published: December 2017

We examined the response of net muscle protein synthesis to ingestion of amino acids after a bout of resistance exercise. A primed, constant infusion ofl-[ ring-2H5]phenylalanine was used to measure net muscle protein balance in three male and three female volunteers on three occasions. Subjects consumed in random order 1 liter of 1) a mixed amino acid (40 g) solution (MAA), 2) an essential amino acid (40 g) solution (EAA), and 3) a placebo solution (PLA). Arterial amino acid concentrations increased ∼150–640% above baseline during ingestion of MAA and EAA. Net muscle protein balance was significantly increased from negative during PLA ingestion (−50 ± 23 nmol ⋅ min−1 ⋅ 100 ml leg volume−1) to positive during MAA ingestion (17 ± 13 nmol ⋅ min−1 ⋅ 100 ml leg volume−1) and EAA (29 ± 14 nmol ⋅ min−1 ⋅ 100 ml leg volume−1; P < 0.05). Because net balance was similar for MAA and EAA, it does not appear necessary to include nonessential amino acids in a formulation designed to elicit an anabolic response from muscle after exercise. We concluded that ingestion of oral essential amino acids results in a change from net muscle protein degradation to net muscle protein synthesis after heavy resistance exercise in humans similar to that seen when the amino acids were infused.
TNF-α impairs insulin signaling and insulin stimulation of glucose uptake in C2C12muscle cells
Authors: del Aguila Luis F. , Claffey Kevin P. , Kirwan John P.
Published: December 2017

Physiological stressors such as sepsis and tissue damage initiate an acute immune response and cause transient systemic insulin resistance. This study was conducted to determine whether tumor necrosis factor-α (TNF-α), a cytokine produced by immune cells during skeletal muscle damage, decreases insulin responsiveness at the cellular level. To examine the molecular mechanisms associated with TNF-α and insulin action, we measured insulin receptor substrate (IRS)-1- and IRS-2-mediated phosphatidylinositol 3-kinase (PI 3-kinase) activation, IRS-1-PI 3-kinase binding, IRS-1 tyrosine phosphorylation, and the phosphorylation of two mitogen-activated protein kinases (MAPK, known as p42MAPKand p44MAPK) in cultured C2C12myotubes. Furthermore, we determined the effects of TNF-α on insulin-stimulated 2-deoxyglucose (2-DG) uptake. We observed that TNF-α impaired insulin stimulation of IRS-1- and IRS-2-mediated PI 3-kinase activation by 54 and 55% ( P< 0.05), respectively. In addition, TNF-α decreased insulin-stimulated IRS-1 tyrosine phosphorylation by 40% ( P < 0.05). Furthermore, TNF-α repressed insulin-induced p42MAPKand p44MAPKtyrosine phosphorylation by 81% ( P < 0.01). TNF-α impairment of insulin signaling activation was accompanied by a decrease ( P < 0.05) in 2-DG uptake in the muscle cells (60 ± 4 vs. 44 ± 6 pmol ⋅ min−1⋅ mg−1). These data suggest that increases in TNF-α may cause insulin resistance in skeletal muscle by inhibiting IRS-1- and IRS-2-mediated PI 3-kinase activation as well as p42MAPKand p44MAPKtyrosine phosphorylation, leading to impaired insulin-stimulated glucose uptake.
Metabolic adjustments during daily torpor in the Djungarian hamster
Authors: Heldmaier Gerhard , Klingenspor Martin , Werneyer Martin , Lampi Brian J. , Brooks Stephen P. J. , Storey Kenneth B.
Published: December 2017

Djungarian hamsters ( Phodopus sungorus) acclimated to a short photoperiod (8:16-h light-dark cycle) display spontaneous daily torpor with ad libitum food availability. The time course of body temperature (Tb), metabolic rate, respiratory quotient (RQ), and substrate and enzyme changes was measured during entrance into torpor and in deep torpor. RQ, blood glucose, and serum lipids are high during the first hours of torpor but then gradually decline, suggesting that glucose is the primary fuel during the first hours of torpor, with a gradual change to lipid utilization. No major changes in enzyme activities were observed during torpor except for inactivation of the pyruvate dehydrogenase (PDH) complex in liver, brown adipose tissue, and heart muscle. PDH inactivation closely correlates with the reduction of total metabolic rate, whereas in brain, kidney, diaphragm, and skeletal muscle, PDH activity was maintained at the initial level. These findings suggest inhibition of carbohydrate oxidation in heart, brown adipose tissue, and liver during entrance into daily torpor.
Effect of AMPK activation on muscle glucose metabolism in conscious rats
Authors: Bergeron Raynald , Russell Raymond R. , Young Lawrence H. , Ren Jian-Ming , Marcucci Melissa , Lee Agnes , Shulman Gerald I.
Published: December 2017

The effect of AMP-activated protein kinase (AMPK) activation on skeletal muscle glucose metabolism was examined in awake rats by infusing them with 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR; 40 mg/kg bolus and 7.5 mg ⋅ kg−1⋅ min−1constant infusion) along with a variable infusion of glucose (49.1 ± 2.4 μmol ⋅ kg−1⋅ min−1) to maintain euglycemia. Activation of AMPK by AICAR caused 2-deoxy-d-[1,2-3H]glucose (2-DG) uptake to increase more than twofold in the soleus and the lateral and medial gastrocnemius compared with saline infusion and occurred without phosphatidylinositol 3-kinase activation. Glucose uptake was also assessed in vitro by use of the epitrochlearis muscle incubated either with AICAR (0.5 mM) or insulin (20 mU/ml) or both in the presence or absence of wortmannin (1.0 μM). AICAR and insulin increased muscle 2-DG uptake rates by ∼2- and 2.7-fold, respectively, compared with basal rates. Combining AICAR and insulin led to a fully additive effect on muscle glucose transport activity. Wortmannin inhibited insulin-stimulated glucose uptake. However, neither wortmannin nor 8-(p-sulfophenyl)-theophylline (10 μM), an adenosine receptor antagonist, inhibited the AICAR-induced activation of glucose uptake. Electrical stimulation led to an about threefold increase in glucose uptake over basal rates, whereas no additive effect was found when AICAR and contractions were combined. In conclusion, the activation of AMPK by AICAR increases skeletal muscle glucose transport activity both in vivo and in vitro. This cellular pathway may play an important role in exercise-induced increase in glucose transport activity.
Cytosolic citrate and malonyl-CoA regulation in rat muscle in vivo
Authors: Saha Asish K. , Laybutt D. Ross , Dean David , Vavvas Demetrios , Sebokova Elena , Ellis Bronwyn , Klimes Iwar , Kraegen Edward W. , Shafrir Eleazar , Ruderman Neil B.
Published: December 2017

In liver, insulin and glucose acutely increase the concentration of malonyl-CoA by dephosphorylating and activating acetyl-CoA carboxylase (ACC). In contrast, in incubated rat skeletal muscle, they appear to act by increasing the cytosolic concentration of citrate, an allosteric activator of ACC, as reflected by increases in the whole cell concentrations of citrate and malate [Saha, A. K., D. Vavvas, T. G. Kurowski, A. Apazidis, L. A. Witters, E. Shafrir, and N. B. Ruderman. Am. J. Physiol. 272 ( Endocrinol. Metab. 35): E641–E648, 1997]. We report here that sustained increases in plasma insulin and glucose may also increase the concentration of malonyl-CoA in rat skeletal muscle in vivo by this mechanism. Thus 70 and 125% increases in malonyl-CoA induced in skeletal muscle by infusions of glucose for 1 and 4 days, respectively, and a twofold increase in its concentration during a 90-min euglycemic-hyperinsulinemic clamp were all associated with significant increases in the sum of whole cell concentrations of citrate and/or malate. Similar correlations were observed in muscle of the hyperinsulinemic fa/fa rat, in denervated muscle, and in muscle of rats infused with insulin for 5 h. In muscle of 48-h-starved rats 3 and 24 h after refeeding, increases in malonyl-CoA were not accompanied by consistent increases in the concentrations of malate or citrate. However, they were associated with a decrease in the whole cell concentration of long-chain fatty acyl-CoA (LCFA-CoA), an allosteric inhibitor of ACC. The results suggest that increases in the concentration of malonyl-CoA, caused in rat muscle in vivo by sustained increases in plasma insulin and glucose or denervation, may be due to increases in the cytosolic concentration of citrate. In contrast, during refeeding after starvation, the increase in malonyl-CoA in muscle is probably due to another mechanism.
Isradipine and insulin sensitivity in hypertensive rats
Authors: Pǐtre Maryse , Gaudreault Nathalie , Santuré Marta , Nadeau André , Bachelard Hélène
Published: December 2017

The present study was designed to investigate the effect of a reduction in blood pressure, by using the calcium channel antagonist isradipine, on insulin sensitivity and vascular responses to insulin in conscious spontaneously hypertensive male rats (SHR). The rats were instrumented with intravascular catheters and pulsed Doppler flow probes to measure blood pressure, heart rate, and blood flows. Insulin sensitivity was assessed by the euglycemic-hyperinsulinemic clamp technique. Two groups of rats received isradipine at a dose of 0.05 or 0.15 mg ⋅ kg−1⋅ h−1, whereas a third group received a continuous infusion of vehicle (15% DMSO). Both doses of isradipine were found to decrease mean blood pressure (−25 ± 4 mmHg at the dose of 0.05 mg ⋅ kg−1⋅ h−1and −20 ± 2 mmHg at the dose of 0.15 mg ⋅ kg−1⋅ h−1) and to improve insulin sensitivity. Moreover, in the rats treated with the low dose of isradipine, we observed vasodilations in renal, superior mesenteric, and hindquarter vascular beds. In the untreated group, the euglycemic infusion of insulin (4 mU ⋅ kg−1⋅ min−1) was found to cause vasoconstrictions in superior mesenteric and hindquarter vascular beds, but no changes in mean blood pressure, heart rate, or renal vascular conductance were found. In contrast, in the isradipine-treated groups, the same dose of insulin was found to produce vasodilations in the renal vascular bed and to abolish the vasoconstrictor responses previously observed. We concluded that short-term treatment with isradipine in SHR can lower blood pressure and improve insulin sensitivity, mainly through hemodynamic factors, as supported by experiments with hydralazine as a positive vasodilator control.
Whole body protein kinetics using Phe and Tyr tracers: an evaluation of the accuracy of approximated flux values
Authors: Short Kevin R. , Meek Shon E. , Moller Niels , Ekberg Karin , Nair K. Sreekumaran
Published: December 2017

Phenylalanine (Phe) kinetics are increasingly used in studies of amino acid kinetics, because the metabolic fate of Phe is limited to incorporation into protein (protein synthesis, Sp) and catabolism via hydroxylation ( Q pt) to tyrosine (Tyr). Besides an infusion of labeled Phe to measure Phe flux ( Q p), a priming dose of Tyr and an independent Tyr tracer are used to measure Tyr flux ( Q t) and Q pt. Alternatively, Q t, Q pt, and Sp can be approximated by using equations, based on Phe and Tyr concentrations in body proteins, that eliminate the need for a Tyr tracer. To evaluate the accuracy of this approach, data were obtained from 12 type I diabetic patients and 24 nondiabetic control subjects who were studied with the full complement of tracers both with and without insulin infusion. Sp approximations closely matched measured values in both groups (mean difference <2%, all values <5%), but the agreement was poor for Q pt (error range = −8 to +43%) and Q t (error range −22 to +41%). Insulin status had no effect on these comparisons. The lower approximation error for Sp vs. Q pt is due to the small contribution (∼10%) of Q pt to Q p. Approximation error for Q pt( r > 0.99) can be explained by variability in the ratio of Tyr to Phe coming from protein breakdown, ( Q t − Q pt)/ Q p. Ideally, all fluxes should be directly measured, but these data suggest that whole body Sp can be approximated with an acceptably small margin of error. However, the same equations do not yield reliably accurate values for Q pt or Q t.
Effects of nonsulfur and sulfur amino acids on the regulation of hepatic enzymes of cysteine metabolism
Authors: Bella Deborah L. , Hahn Christine , Stipanuk Martha H.
Published: December 2017

To determine the role of nonsulfur vs. sulfur amino acids in regulation of cysteine metabolism, rats were fed a basal diet or diets supplemented with a mixture of nonsulfur amino acids (AA), sulfur amino acids (SAA), or both for 3 wk. Hepatic cysteine-sulfinate decarboxylase (CSDC), cysteine dioxygenase (CDO), and γ-glutamylcysteine synthetase (GCS) activity, concentration, and mRNA abundance were measured. Supplementation with AA alone had no effect on any of these measures. Supplementation of the basal diet with SAA, with or without AA, resulted in a higher CDO concentration (32–45 times basal), a lower CSDC mRNA level (49–64% of basal), and a lower GCS-heavy subunit mRNA level (70–76%). The presence of excess SAA and AA together resulted in an additional type of regulation: a lower specific activity of all three enzymes was observed in rats fed diets with an excess of AA and SAA. Both SAA and AA played a role in regulation of these three enzymes of cysteine metabolism, but SAA had the dominant effects, and effects of AA were not observed in the absence of SAA.
PDH activation by dichloroacetate reduces TCA cycle intermediates at rest but not during exercise in humans
Authors: Gibala Martin J. , Saltin Bengt
Published: December 2017

We hypothesized that dichloroacetate (DCA), which stimulates the pyruvate dehydrogenase complex (PDH), would attenuate the increase in muscle tricarboxylic acid cycle intermediates (TCAI) during exercise by increasing the oxidative disposal of pyruvate and attenuating the flux through anaplerotic pathways. Six subjects were infused with either saline (Con) or DCA (100 mg/kg body mass) and then performed a moderate leg kicking exercise for 15 min, followed immediately by intense exercise until exhaustion (Exh; ∼4 min). Resting active fraction of PDH (PDHa) was markedly increased ( P ≤ 0.05) after DCA vs. Con (2.65 ± 0.27 vs. 0.64 ± 0.07 mmol ⋅ min−1 ⋅ kg wet wt−1); however, there were no differences between trials after 1 or 15 min of exercise or at Exh. The sum of five measured TCAI (ΣTCAI; ∼90% of total TCAI pool) was lower ( P ≤ 0.05) after DCA vs. Con at rest (0.78 ± 0.11 vs. 1.52 ± 0.23 mmol/kg dry wt, respectively). However, the net increase in muscle TCAI during the first minute of exercise was higher ( P≤ 0.05) in the DCA trial vs. Con (3.05 ± 0.45 vs. 2.44 ± 0.55 mmol ⋅ min−1 ⋅ kg dry wt−1, respectively), and consequently, the ΣTCAI was not different between trials during exercise. We conclude that DCA reduced TCAI pool size at rest by increasing the flux through PDH and diverting pyruvate away from anaplerotic pathways. The reason for the similar absolute increase in TCAI during exercise is not clear but may be related to 1) an initial mismatch between glycolytic flux and PDH flux that provided sufficient pyruvate for anaplerosis in both trials; or 2) a transient inhibition of PDH flux during the DCA trial due to an elevated resting acetyl-CoA-to-CoASH ratio, which augmented the anaplerotic flux of carbon during the rest-to-work transition.
Altered circadian responses to light in streptozotocin-induced diabetic mice
Authors: Challet Etienne , van Reeth Olivier , Turek Fred W.
Published: December 2017

Diabetes mellitus affects the daily expression of many behavioral and metabolic processes. Recent studies indicate that changes in brain glucose metabolism alter the entraining effects of light of the circadian pacemaker. To test whether diabetes-associated diurnal changes are related to alterations in the responses of the circadian pacemaker to light, photic phase resetting of the circadian rhythm of locomotor activity was analyzed in diabetic mice housed in constant darkness. Multiple low doses of streptozotocin, which damages pancreatic β-insulin-producing cells, were used to render C57BL/6J mice mildly diabetic. In those mice treated with streptozotocin, serum glucose was increased by 25% and circadian responses to light either were increased by 40% for phase delays or were close to those observed in control animals for phase advances. Furthermore, insulin-induced hypoglycemia normalized light-induced phase delays in diabetic animals, without altering those in nondiabetic mice. These results show that abnormalities of daily temporal organization associated with diabetes can result from altered circadian responses to the daily variation in ambient light. Such alterations could be normalized with appropriate insulin therapy.
Low-dose T3 improves the bed rest model of simulated weightlessness in men and women
Authors: Lovejoy Jennifer C. , Smith Steven R. , Zachwieja Jeffrey J. , Bray George A. , Windhauser Marlene M. , Wickersham Peter J. , Veldhuis Johannes D. , Tulley Richard , de la Bretonne Jacques A.
Published: December 2017

This study tested the hypothesis that low-dose 3,5,3′-triiodothyronine (T3) administration during prolonged bed rest improves the ground-based model of spaceflight. Nine men (36.4 ± 1.3 yr) and five women (34.2 ± 2.1 yr) were studied. After a 5-day inpatient baseline period, subjects were placed at total bed rest with 6° head-down tilt for 28 days followed by 5-day recovery. Fifty micrograms per day of T3( n = 8) or placebo ( n = 6) were given during bed rest. Serum T3 concentrations increased twofold, whereas thyroid-stimulating hormone was suppressed in treated subjects. T3-treated subjects showed significantly greater negative nitrogen balance and lost more weight ( P = 0.02) and lean mass ( P < 0.0001) than placebo subjects. Protein breakdown (whole body [13C]leucine kinetics) increased 31% in the T3 group but only 8% in the placebo group. T3-treated women experienced greater changes in leucine turnover than men, despite equivalent weight loss. Insulin sensitivity fell by 50% during bed rest in all subjects ( P = 0.005), but growth hormone release and insulin release were largely unaffected. In conclusion, addition of low-dose T3 to the bed rest model of muscle unloading improves the ground-based simulation of spaceflight and unmasks several important gender differences.
Noninvasive tracing of human liver metabolism: comparison of phenylacetate and apoB-100 to sample glutamine
Authors: Diraison Frédérique , Large Valérie , Maugeais Cyrille , Krempf Michel , Beylot Michel
Published: December 2017

The labeling pattern of hepatic glutamine during infusion of [3-13C]lactate provides information on liver intermediary metabolism and allows us to correct apparent gluconeogenic rates for isotopic dilution in the oxaloacetate (OAA) pool. Liver glutamine can be sampled by its conjugation with phenylacetate to form phenylacetylglutamine (PAGN) but also by purifying the glutamine of the apolipoproteinB-100 of very low-density lipoprotein (apoB-100-VLDL). We compared these methods in normal and non-insulin dependent diabetes subjects. We tested also whether apoB-100-VLDL alanine enrichment could solve the problem of dilution of gluconeogenic precursor enrichments between peripheral blood and liver (prehepatic dilution). In both normal and diabetic subjects, the labeling patterns of glutamine obtained from PAGN or apoB-100-VLDL were comparable. Therefore, metabolic fluxes and correction factors for dilution in the OAA pool were also comparable. With both methods, gluconeogenic rates were not increased in diabetic patients. Use of the enrichment of apoB-100-VLDL alanine to correct for prehepatic dilution led to high estimates of gluconeogenesis; it remains uncertain whether this enrichment provides a correct estimate of liver pyruvate enrichment.
Threonine phosphorylations induced by RX-871024 and insulin secretagogues in βTC6-F7 cells
Authors: An Jie , Zhao Genshi , Churgay Lisa M. , Osborne John J. , Hale John E. , Becker Gerald W. , Gold Gerald , Stramm Lawrence E. , Shi Yuguang
Published: December 2017

Treatment of the pancreatic β-cell line βTC6-F7 with an imidazoline compound, RX-871024, KCl, or tolbutamide resulted in increased threonine phosphorylation of a 220-kDa protein (p220) concurrent with enhanced insulin secretion, which can be partially antagonized by diazoxide, an ATP-sensitive potassium (KATP) channel activator. Although phosphorylation of p220 was regulated by cytoplasmic free calcium concentration ([Ca2+]i), membrane depolarization alone was not sufficient to induce phosphorylation. Phosphorylation of p220 also was not directly mediated by protein kinase A, protein kinase C, or insulin exocytosis. Analysis of subcellular fractions indicated that p220 is a hydrophilic protein localized exclusively in the cytosol. Subsequently, p220 was purified to homogeneity, sequenced, and identified as nonmuscle myosin heavy chain-A (MHC-A). Stimulation of threonine phosphorylation of nonmuscle MHC-A by KCl treatment also resulted in increased phosphorylation of a 40-kDa protein, which was coimmunoprecipitated by antibody to MHC-A. Our results suggest that both nonmuscle MHC-A and the 40-kDa protein may play roles in regulating signal transduction, leading to insulin secretion.
Angiotensin II induces insulin resistance independent of changes in interstitial insulin
Authors: Richey Joyce M. , Ader Marilyn , Moore Donna , Bergman Richard N.
Published: December 2017

We set out to examine whether angiotensin-driven hypertension can alter insulin action and whether these changes are reflected as changes in interstitial insulin (the signal to which insulin-sensitive cells respond to increase glucose uptake). To this end, we measured hemodynamic parameters, glucose turnover, and insulin dynamics in both plasma and interstitial fluid (lymph) during hyperinsulinemic euglycemic clamps in anesthetized dogs, with or without simultaneous infusions of angiotensin II (ANG II). Hyperinsulinemia per se failed to alter mean arterial pressure, heart rate, or femoral blood flow. ANG II infusion resulted in increased mean arterial pressure (68 ± 16 to 94 ± 14 mmHg, P < 0.001) with a compensatory decrease in heart rate (110 ± 7 vs. 86 ± 4 mmHg, P < 0.05). Peripheral resistance was significantly increased by ANG II from 0.434 to 0.507 mmHg ⋅ ml−1⋅ min ( P < 0.05). ANG II infusion increased femoral artery blood flow (176 ± 4 to 187 ± 5 ml/min, P < 0.05) and resulted in additional increases in both plasma and lymph insulin (93 ± 20 to 122 ± 13 μU/ml and 30 ± 4 to 45 ± 8 μU/ml, P < 0.05). However, glucose uptake was not significantly altered and actually had a tendency to be lower (5.9 ± 1.2 vs. 5.4 ± 0.7 mg ⋅ kg−1⋅ min−1, P > 0.10). Mimicking of the ANG II-induced hyperinsulinemia resulted in an additional increase in glucose uptake. These data imply that ANG II induces insulin resistance by an effect independent of a reduction in interstitial insulin.