bluuebunny/crossref_metadata_2025 huggingface dataset:
Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise
Authors: Horowitz Jeffrey F. , Mora-Rodriguez Ricardo , Byerley Lauri O. , Coyle Edward F.
Published: December 2017

This study determined if the suppression of lipolysis after preexercise carbohydrate ingestion reduces fat oxidation during exercise. Six healthy, active men cycled 60 min at 44 ± 2% peak oxygen consumption, exactly 1 h after ingesting 0.8 g/kg of glucose (Glc) or fructose (Fru) or after an overnight fast (Fast). The mean plasma insulin concentration during the 50 min before exercise was different among Fast, Fru, and Glc (8 ± 1, 17 ± 1, and 38 ± 5 μU/ml, respectively; P< 0.05). After 25 min of exercise, whole body lipolysis was 6.9 ± 0.2, 4.3 ± 0.3, and 3.2 ± 0.5 μmol ⋅ kg−1⋅ min−1and fat oxidation was 6.1 ± 0.2, 4.2 ± 0.5, and 3.1 ± 0.3 μmol ⋅ kg−1⋅ min−1during Fast, Fru, and Glc, respectively (all P < 0.05). During Fast, fat oxidation was less than lipolysis ( P < 0.05), whereas fat oxidation approximately equaled lipolysis during Fru and Glc. In an additional trial, the same subjects ingested glucose (0.8 g/kg) 1 h before exercise and lipolysis was simultaneously increased by infusing Intralipid and heparin throughout the resting and exercise periods (Glc+Lipid). This elevation of lipolysis during Glc+Lipid increased fat oxidation 30% above Glc (4.0 ± 0.4 vs. 3.1 ± 0.3 μmol ⋅ kg−1⋅ min−1; P < 0.05), confirming that lipolysis limited fat oxidation. In summary, small elevations in plasma insulin before exercise suppressed lipolysis during exercise to the point at which it equaled and appeared to limit fat oxidation.
Parathyroid Ca2+-conducting currents are modulated by muscarinic receptor agonists and antagonists
Authors: Chang Wenhan , Chen Tsui-Hua , Pratt Stacy A. , Yen Benedict , Fu Michael , Shoback Dolores
Published: December 2017

Parathyroid cells express Ca2+-conducting cation currents, which are activated by raising the extracellular Ca2+concentration ([Ca2+]o) and blocked by dihydropyridines. We found that acetylcholine (ACh) inhibited these currents in a reversible, dose-dependent manner (50% inhibitory concentration ≈10−8M). The inhibitory effects could be mimicked by the agonist (+)-muscarine. The effects of ACh were blunted by the antagonist atropine and reversed by removing ATP from the pipette solution. (+)-Muscarine enhanced the adenosine 3′,5′-cyclic monophosphate (cAMP) production by 30% but had no effect on inositol phosphate accumulation in parathyroid cells. Oligonucleotide primers, based on sequences of known muscarinic receptors (M1-M5), were used in reverse transcriptase-polymerase chain reaction (RT-PCR) to amplify receptor cDNA from parathyroid poly (A)+RNA. RT-PCR products displayed >90% nucleotide sequence identity to human M2- and M4-receptor cDNAs. Expression of M2-receptor protein was further confirmed by immunoblotting and immunocytochemistry. Thus parathyroid cells express muscarinic receptors of M2and possibly M4subtypes. These receptors may couple to dihydropyridine-sensitive, cation-selective currents through the activation of adenylate cyclase and ATP-dependent pathways in these cells.
Growth hormone induces detergent insolubility of GH receptors in IM-9 cells
Authors: Goldsmith Jeffrey F. , Lee Sung Joong , Jiang Jing , Frank Stuart J.
Published: December 2017

In this study, we examined human growth hormone (hGH)-induced changes in nonionic detergent solubility characteristics of its receptor (hGHR). Exposure of IM-9 cells to hGH caused a time- and concentration-dependent loss of immunoblottable detergent-extractable hGHRs and a corresponding accumulation of receptors in a detergent-insoluble pool. At 37°C, the loss of detergent-soluble and the accumulation of detergent-insoluble hGHRs both preceded hGH-induced loss of total cell hGHRs. The detergent-insoluble receptor pool was progressively enriched in an apparent disulfide-linked form of the hGHR. Exposure to hGH at 4°C allowed hGH-induced hGHR disulfide linkage but did not promote changes in receptor detergent solubility, indicating that hGHR detergent insolubility cannot be explained solely by the formation of that linkage. Experiments carried out with hGH at 20°C and with the phorbol ester, phorbol-12,13-myristate acetate, at 37°C indicated that loss of detergent-soluble hGHRs can be uncoupled from accumulation of detergent-insoluble receptors. From these data, we envision at least two related, but separable, trafficking pathways taken by hGHRs after their surface interaction with hGH: 1) ligand-mediated endocytosis and degradation (accounting for only some of the receptors lost from the detergent-soluble fraction) and 2) ligand-mediated accumulation in a detergent-insoluble subcellular fraction (arising largely from receptors redistributed from the detergent-soluble fraction).
High-fat feeding alters both basal and stress-induced hypothalamic-pituitary-adrenal activity in the rat
Authors: Tannenbaum Beth M. , Brindley David N. , Tannenbaum Gloria S. , Dallman Mary F. , McArthur M. Dawn , Meaney Michael J.
Published: December 2017

High-fat feeding induces insulin resistance and increases the risk for the development of diabetes and coronary artery disease. Glucocorticoids exacerbate this hyperinsulinemic state, rendering an individual at further risk for chronic disease. The present studies were undertaken to determine whether dietary fat-induced increases in corticosterone (B) reflect alterations in the regulatory components of the hypothalamic-pituitary-adrenal (HPA) axis. Adult male rats were maintained on a high-fat (20%) or control (4%) diet for varying periods of time. Marked elevations in light-phase spontaneous basal B levels were evident as early as 7 days after fat diet onset, and B concentrations remained significantly elevated up to 21 days after fat diet onset compared with controls. In contrast, there were no significant effects on any parameters of spontaneous growth hormone secretory profiles, thus providing support for the specificity of the effects on the HPA axis. In a second study, all groups of rats fed the high-fat diet for 1, 9, or 12 wk exhibited significantly elevated levels of plasma adrenocorticotropic hormone, B, fatty acid, and glucose before, during, and/or at 20, 60, and/or 120 min after the termination of a restraint stress. Furthermore, 12-wk fat-fed animals showed a significant resistance to insulin compared with normally fed controls. There were no differences in negative feedback efficacy in high-fat-fed rats vs. controls. Taken together, these results suggest that dietary fat intake acts as a background form of chronic stress, elevating basal B levels and enhancing HPA responses to stress.
Atrial natriuretic peptide induces acrosomal exocytosis of human spermatozoa
Authors: Rotem Ronit , Zamir Nadav , Keynan Nurit , Barkan Dalit , Breitbart Haim , Naor Zvi
Published: December 2017

Acrosomal exocytosis in mammalian spermatozoa is a process essential for fertilization. We report here that atrial natriuretic peptide (ANP) markedly stimulates acrosomal exocytosis of capacitated human spermatozoa. Typically, ANP exerts some of its actions via activation of the ANP receptor (ANPR-A), a particulate guanylyl cyclase-linked receptor, and subsequent formation of guanosine 3′,5′-cyclic monophosphate (cGMP). We found that ANP-stimulated acrosome reaction was inhibited by the competitive ANPR-A antagonist anantin, indicating a receptor-mediated process. A linear fragment of ANP, ANP-(13—28), and another ANP-like compound, brain natriuretic peptide, were inactive. The stimulatory effect of ANP on acrosome reaction was mimicked by the permeable cGMP analog, 8-bromo-cGMP (8-BrcGMP). Addition of the protein kinase C (PKC) inhibitors, staurosporine and GF-109203X, resulted in a dose-related inhibition of ANP-induced acrosome reaction. Also, downregulation of endogeneous PKC activity resulted in inhibition of ANP- but not 8-BrcGMP-induced acrosome reaction. Removal of extracellular Ca2+abolished ANP-induced acrosome reaction. Thus ANP via Ca2+influx, PKC activation, and stimulation of particulate guanylyl cyclase may play a role in the induction of acrosome reaction of human spermatozoa.
Alterations in basal nutrient metabolism increase resting energy expenditure in sickle cell disease
Authors: Borel Myfanwy J. , Buchowski Maciej S. , Turner Ernest A. , Peeler Benjamin B. , Goldstein Richard E. , Flakoll Paul J.
Published: December 2017

Basal rates of whole body protein, glucose, and lipid metabolism and resting energy expenditure (REE) were measured in eight African-American sickle cell disease (SCD) patients and in six African-American controls. Catheters were placed 1) in an antecubital vein for stable isotope infusion and 2) in a heated hand vein for arterialized venous blood. Breath and blood were collected during the last 30 min of the 2.5-h study, and REE was measured by indirect calorimetry. REE [128 ± 5 vs. 111 ± 1 kJ ⋅ kg fat-free mass (FFM)−1 ⋅ day−1; P < 0.05 vs. controls] was 15% greater in the SCD patients. Whole body protein breakdown (5.0 ± 0.3 vs. 3.8 ± 0.2 mg ⋅ kg FFM−1 ⋅ min−1; P < 0.05 vs. controls) and protein synthesis (4.4 ± 0.3 vs. 3.2 ± 0.2 mg ⋅ kg FFM−1 ⋅ min−1; P< 0.05 vs. controls) were 32 and 38% greater, respectively, in the SCD patients, but whole body amino acid oxidation was similar (0.58 ± 0.03 vs. 0.66 ± 0.03 mg ⋅ kg FFM−1 ⋅ min−1). Measures of whole body glucose and lipid metabolism were not significantly different between the groups. The additional energy required for the greater rates of whole body protein breakdown and synthesis caused by SCD contributes significantly to the observed increase in REE, suggesting that dietary energy and protein requirements are enhanced in SCD patients.
Urate uptake and lowered ATP levels in human muscle after high-intensity intermittent exercise
Authors: Hellsten Y. , Sjödin B. , Richter E. A. , Bangsbo J.
Published: December 2017

The exchange of purines in exercised and rested muscle and their relation to muscle ATP levels after intense intermittent exercise were investigated. Seven subjects performed one-legged knee extensor exercise on the following two occasions: without (control; C) and with (high purines; HP) additional arm exercise. There was a greater net release of hypoxanthine by the exercised muscle during the recovery period in HP compared with C [185 ± 44 vs. 101 ± 30 (SE) μmol/kg muscle; P < 0.05]. During recovery, the arterial urate concentration was higher in HP compared with C (peak: 585 ± 48 vs. 355 ± 20 μmol/l; P < 0.05). The exercised but not the rested muscle extracted a marked amount of urate (330 μmol/kg muscle) from plasma in the HP trial. Muscle ATP levels after 90 min of recovery in HP were lower than at rest (24.3 ± 0.6 vs. 20.1 ± 1.1 mmol/kg dry wt). The present data suggest that a single session of long-term high-intensity intermittent exercise causes a significant release of purines from the muscle into blood, which contributes to a sustained lowered level of the muscle ATP concentration. Furthermore, intensely exercised muscle extracts urate when plasma urate is elevated, an event that may be of importance for the replenishment of oxidized muscle urate stores.
Ovine fetal leucine kinetics and protein metabolism during decreased oxygen availability
Authors: Milley J. Ross
Published: December 2017

The fetus depends on an uninterrupted supply of oxygen to provide energy, not only for basal metabolism but also for the metabolic costs of growth. By curtailing the metabolically expensive processes of protein turnover, the fetus could conserve energy when oxygen availability is limited. Therefore, this investigation was performed to find whether protein synthesis and breakdown are diminished during decreased fetal oxygen availability. Furthermore, if these conditions reduce fetal growth, protein synthesis should be affected more than breakdown so that protein accretion, an important component of fetal growth, also falls. In eight chronically prepared fetal lambs, we compared leucine kinetics (reciprocal pool model) during control conditions with measurements made during maternal hypoxia, a condition that limits fetal oxygen availability. Decreased fetal oxygen availability (−43%; P < 0.001) reduced fetal oxygen consumption (−16%; P < 0.01), as well as both the uptake of leucine across the placenta (−48%; P < 0.001) and its rate of decarboxylation (−30%; P < 0.001). Fetal protein synthesis decreased (−32%; P < 0.001) to a greater extent than proteolysis (−22%; P < 0.001). Consequently, fetal protein accretion, an important component of fetal growth, also decreased (−62%; P < 0.001). We calculate that the reduction in fetal protein synthesis and breakdown, both processes that require intracellular expenditure of ATP, decreased fetal energy needs sufficiently to account for most, if not all, of the decrease measured in fetal oxygen consumption.
Time course of insulin action on tissue-specific intracellular glucose metabolism in normal rats
Authors: Koopmans Sietse J. , Mandarino Lawrence , Defronzo Ralph A.
Published: December 2017

We investigated the time course of insulin action in conscious rats exposed to constant physiological hyperinsulinemia (∼100 mU/l) while maintaining euglycemia (∼100 mg/dl) for 0, 0.5, 2, 4, 8, or 12 h. [3-3H]glucose was infused to quantitate whole body glucose disposal (rate of disappearance, Rd), glycolysis (generation of3H2O in plasma), hepatic glucose production (HGP), and skeletal muscle and liver glycogen synthesis ([3-3H]glucose incorporation into glycogen and time-dependent change in tissue glycogen concentration). The basal Rd, which equals HGP, was 6.0 ± 0.3 mg ⋅ kg−1⋅ min−1. With increased duration of hyperinsulinemia from 0 to 0.5 to 2 to 4 h, Rdincreased from 6.0 ± 0.3 to 21.0 ± 1.1 to 24.1 ± 1.5 to 26.6 ± 0.6 mg ⋅ kg−1⋅ min−1( P < 0.05 for 2 and 4 h vs. 0.5 h). During the first 2 h the increase in Rdwas explained by parallel increases in glycolysis and glycogen synthesis. From 2 to 4 h the further increase in Rdwas entirely due to an increase in glycolysis without change in glycogen synthesis. From 4 to 8 to 12 h of hyperinsulinemia, Rddecreased by 19% from 26.6 ± 0.6 to 24.1 ± 1.1 to 21.6 ± 1.8 mg ⋅ kg−1⋅ min−1( P < 0.05 for 8 h vs. 4 h and 12 h vs. 8 h). The progressive decline in Rd, in the face of constant hyperinsulinemia, occurred despite a slight increase (8–14%) in glycolysis and was completely explained by a marked decrease (64%) in muscle glycogen synthesis. In contrast, liver glycogen synthesis increased fourfold, indicating an independent regulation of muscle and liver glycogen synthesis by long-term hyperinsulinemia. In the liver, during the entire 12-h period of insulin stimulation, the contribution of the direct (from glucose) and the indirect (from C-3 fragments) pathways to net glycogen formation remained constant at 77 ± 5 and 23 ± 5%, respectively. HGP remained suppressed throughout the 12-h period of hyperinsulinemia.
Effect of aging on β-adrenergically mediated thermogenesis in men
Authors: Kerckhoffs Daniëlle A. J. M. , Blaak Ellen E. , Van Baak Marleen A. , Saris Wim H. M.
Published: December 2017

The age-dependent alterations in β-adrenergically mediated thermogenesis were investigated in 11 young (mean ± SE age: 21.9 ± 0.5 yr) and 9 older (52.9 ± 2.1 yr) men during intravenous infusion of the nonselective β-agonist isoprenaline (Iso). The older men had higher basal plasma norepinephrine (327.7 ± 35.8 vs. 159.0 ± 18.2 pg/ml, P < 0.001) and epinephrine (75.1 ± 18.1 vs. 29.1 ± 5.3 pg/ml, P < 0.05) concentrations than the young. The β-adrenergically mediated thermogenesis was diminished in the older men, as reflected by the significantly higher plasma Iso concentration needed to increase resting energy expenditure by 15% (236.1 ± 51.0 vs. 107.6 ± 11.4 pg/ml, P < 0.05). Additionally, both dose (39.4 ± 6.6 vs. 19.1 ± 1.5 ng ⋅ kg fat-free mass−1 ⋅ min−1, P < 0.01) and plasma concentration (332.2 ± 59.1 vs. 119.3 ± 14.0 pg/ml, P < 0.01) of Iso needed to increase resting heart rate by 25 beats/min were higher in older than in younger subjects, suggesting that the age-related decline in β-adrenergic sensitivity is a generalized defect not related to a specific tissue or response. In conclusion, aging is associated with a diminished β-adrenergically mediated thermogenesis. This blunted thermogenic response may contribute to a positive energy balance and thus promote increased fat storage and obesity.
Maternal hyperglycemia alters glucose transport and utilization in mouse preimplantation embryos
Authors: Moley Kelle H. , Chi Maggie M.-Y. , Mueckler Mike M.
Published: December 2017

Glucose utilization was studied in preimplantation embryos from normal and diabetic mice. With use of ultramicrofluorometric enzyme assays, intraembryonic free glucose in single embryos recovered from control and streptozotocin-induced hyperglycemic mice was measured at 24, 48, 72, and 96 h after mating. Free glucose concentrations dropped significantly in diabetics at 48 and 96 h, corresponding to the two-cell and blastocyst stages (48 h: diabetic 0.23 ± 0.09 vs. control 2.30 ± 0.43 mmol/kg wet wt; P < 0.001; 96 h: diabetic 0.31 ± 0.29 vs. control 5.12 ± 0.17 mmol/kg wet wt; P < 0.001). Hexokinase activity was not significantly different in the same groups. Transport was then compared using nonradioactive 2-deoxyglucose uptake and microfluorometric enzyme assays. The 2-deoxyglucose uptake was significantly lower at both 48 and 96 h in embryos from diabetic vs. control mice (48 h diabetic, 0.037 ± 0.003; control, 0.091 ± 0.021 mmol ⋅ kg wet wt−1⋅ 10 min−1, P < 0.05; 96 h diabetic, 0.249 ± 0.008; control, 0.389 ± 0.007 mmol ⋅ kg wet wt−1⋅ 10 min−1, P < 0.02). When competitive quantitative reverse transcription-polymerase chain reaction was used, there was 44 and 68% reduction in the GLUT-1 mRNA at 48 h ( P < 0.001) and 96 h ( P < 0.05), respectively, in diabetic vs. control mice. GLUT-2 and GLUT-3 mRNA values were decreased 63 and 77%, respectively ( P < 0.01, P < 0.01) at 96 h. Quantitative immunofluorescence microscopy demonstrated 49 ± 6 and 66 ± 4% less GLUT-1 protein at 48 and 96 h and 90 ± 5 and 84 ± 6% less GLUT-2 and -3 protein, respectively, at 96 h in diabetic embryos. These findings suggest that, in response to a maternal diabetic state, preimplantation mouse embryos experience a decrease in glucose utilization directly related to a decrease in glucose transport at both the mRNA and protein levels.
Relative contributions of a CVO and the microvascular bed to delivery of blood-borne IL-1α to the brain
Authors: Maness Lawrence M. , Kastin Abba J. , Banks William A.
Published: December 2017

Diffusion from brain regions lacking a blood-brain barrier (BBB) and saturable transport across capillaries are possible pathways for the entry of blood-borne interleukin-1α into the central nervous system (CNS). To assess the involvement of these putative routes, mice received intravenous injections of radioiodinated interleukin-1α, and their brains were subjected to emulsion autoradiography. The resulting patterns of silver grain distribution showed that diffusion of interleukin-1α from the choroid plexus and the subfornical organ was greatly restricted. These restrictive properties were quantified by the determination of D1/2values, the distances needed for the concentration of silver grains to decrease by one-half. Within several brain regions, a subset of the microvasculature indicated transport of interleukin-1α across the BBB. Individual microvessels showed different patterns of transport ranging from robust to absent. The high degree of containment of blood-borne interleukin-1α within the regions lacking a BBB indicates that these sites cannot account for total delivery of the cytokine into the brain and suggests instead that the microvascular network may serve as the major route of entry into the CNS.
IGF-I increases forearm blood flow without increasing forearm glucose uptake
Authors: Pendergrass Merri , Fazioni Elisa , Collins Darlene , DeFronzo Ralph A.
Published: December 2017

Decreased insulin-mediated muscle glucose uptake is a characteristic feature of non-insulin-dependent diabetes mellitus and other insulin-resistant states. It has been suggested that an impairment in the ability of insulin to augment limb blood flow, resulting in diminished glucose delivery to muscle, may contribute to this abnormality. In this study, we used human insulin-like growth factor (IGF) I in conjunction with the forearm balance technique to determine whether forearm glucose uptake could be stimulated by increasing blood flow without directly stimulating the intrinsic ability of the muscle to extract glucose. IGF-I was infused intra-arterially in healthy controls at a rate of either 0.4 μg ⋅ kg−1 ⋅ min−1(high IGF) or 0.04 μg ⋅ kg−1 ⋅ min−1(low IGF) for 140 min. With high IGF, forearm blood flow increased approximately twofold (34 ± 3 vs. 64 ± 8 ml ⋅ min−1 ⋅ l forearm volume−1, P < 0.01), and arteriovenous glucose concentration difference (a-v difference) increased modestly (0.19 ± 0.05 vs. 0.31 ± 0.08 mM, P = 0.32), resulting in an increased forearm glucose uptake (6.4 ± 1.7 vs. 21.7 ± 7.4 μmol ⋅ min−1 ⋅ l forearm volume−1, P = 0.09 vs. basal). With low IGF, forearm blood flow increased by 59% (29 ± 4 vs. 46 ± 9 ml ⋅ min−1 ⋅ l forearm volume−1, P < 0.05) and was associated with a proportional decrease in the a-v difference (0.29 ± 0.04 vs. 0.18 ± 0.05 mM, P < 0.05). Forearm glucose uptake therefore was not significantly different from basal values (7.6 ± 0.6 vs. 6.9 ± 1.8 μmol ⋅ min−1 ⋅ kg−1). These data demonstrate that increasing blood flow without increasing the intrinsic ability of the muscle to extract glucose does not increase forearm muscle glucose uptake.
Response of skeletal muscle protein synthesis to insulin in suckling pigs decreases with development
Authors: Wray-Cahen Diane , Nguyen Hanh V. , Burrin Douglas G. , Beckett Philip R. , Fiorotto Marta L. , Reeds Peter J. , Wester Timothy J. , Davis Teresa A.
Published: December 2017

The elevated rate of muscle protein deposition in the neonate is largely due to an enhanced stimulation of skeletal muscle protein synthesis by feeding. To examine the role of insulin in this response, hyperinsulinemic-euglycemic-amino acid clamps were performed in 7- and 26-day-old pigs. Pigs were infused with 0, 30, 100, or 1,000 ng ⋅ kg−0.66 ⋅ min−1of insulin to mimic the plasma insulin levels observed under fasted, fed, refed, and supraphysiological conditions, respectively. Whole body amino acid disposal was determined from the rate of infusion of an amino acid mixture necessary to maintain plasma essential amino acid concentrations near their basal fasting levels. A flooding dose ofl-[4-3H]phenylalanine was used to measure skeletal muscle protein synthesis. Whole body amino acid disposal increased progressively as the insulin infusion rate increased, and this response was greater in 7- than in 26-day-old pigs. Skeletal muscle protein synthesis was stimulated by insulin, and this response was maximal at a low insulin infusion rate (30 ng ⋅ kg−0.66 ⋅ min−1). The stimulation of muscle protein synthesis by insulin was also greater in 7- than in 26- day-old pigs. These data suggest that muscle protein synthesis is more sensitive to insulin than whole body amino acid disposal. The results further suggest that insulin is a central regulatory factor in the elevated rate of muscle protein deposition and the increased response of skeletal muscle protein synthesis to feeding in the neonate.
Simultaneous time-varying systemic appearance of oral and hepatic glucose in adults monitored with stable isotopes
Authors: Livesey G. , Wilson P. D. G. , Dainty J. R. , Brown J. C. , Faulks R. M. , Roe M. A. , Newman T. A. , Eagles J. , Mellon F. A. , Greenwood R. H.
Published: December 2017

The rates (and extent) of appearance of glucose in arterialized plasma from an oral glucose load and from liver (RaO, RaH) can be estimated in humans using radioisotopes, but estimates vary among laboratories. We investigated the use of stable isotopes and undertook 22 primed intravenous infusions ofd-[6,6-2H2]glucose with an oral load includingd-[13C6]glucose in healthy humans. The effective glucose pool volume (VS) had a lower limit of 230 ml/kg body weight (cf. 130 ml/kg commonly assumed). This VSin Steele’s one-compartment model of glucose kinetics gave a systemic appearance from a 50-g oral glucose load per 70 kg body weight of 96 ± 3% of that ingested, which compared with a theoretical value of ∼95%. Mari’s two-compartment model gave 100 ± 3%. The two models gave practically identical RaOand RaHat each point in time and a plateau in the cumulative RaOwhen absorption was complete. Less than 3% of13C was recycled to [13C3]glucose, suggesting that recycling errors were practically negligible in this study. Causes of variation among laboratories are identified. We conclude that stable isotopes provide a reliable and safe alternative to radioactive isotopes in these studies.
Regulation of skeletal muscle UCP-2 and UCP-3 gene expression by exercise and denervation
Authors: Cortright Ronald N. , Zheng Donghai , Jones Jared P. , Fluckey James D. , DiCarlo Stephen E. , Grujic Danica , Lowell Bradford B. , Dohm G. Lynis
Published: December 2017

The factors that regulate gene expression of uncoupling proteins 2 and 3 (UCP-2 and UCP-3) in skeletal muscle are poorly understood, but both genes are clearly responsive to the metabolic state of the organism. Therefore, we tested the hypothesis that denervation and acute and/or chronic exercise (factors that profoundly affect metabolism) would alter UCP-2 and UCP-3 gene expression. For the denervation studies, the sciatic nerve of rat and mouse hindlimb was sectioned in one leg while the contralateral limb served as control. Northern blot analysis revealed that denervation was associated with a 331% increase ( P < 0.001) in UCP-3 mRNA and a 200% increase ( P < 0.01) in UCP-2 mRNA levels in rat mixed gastrocnemius (MG) muscle. In contrast, denervation caused a 53% decrease ( P< 0.001) in UCP-3 and a 63% increase ( P < 0.01) in UCP-2 mRNA levels in mouse MG. After acute exercise (2-h treadmill running), rat UCP-3 mRNA levels were elevated (vs. sedentary control) 252% ( P < 0.0001) in white gastrocnemius and 63% ( P < 0.05) in red gastrocnemius muscles, whereas UCP-2 levels were unaffected. To a lesser extent, elevations in UCP-3 mRNA (22%; P < 0.01) and UCP-2 mRNA (55%; P < 0.01) levels were observed after acute exercise in the mouse MG. There were no changes in either UCP-2 or UCP-3 mRNA levels after chronic exercise (9 wk of wheel running). These results indicate that acute exercise and denervation regulate gene expression of skeletal muscle UCPs.
Diazoxide-induced insulin deficiency greatly reduced muscle protein synthesis in rats: involvement of eIF4E
Authors: Sinaud Sandrine , Balage Michèle , Bayle Gérard , Dardevet Dominique , Vary Thomas C. , Kimball Scot R. , Jefferson Leonard S. , Grizard Jean
Published: December 2017

We have investigated the effect of a postprandial acute insulin deficiency induced by diazoxide injection on rat skeletal muscle protein synthesis. Diazoxide administration lowered plasma insulin >85% within 3 h after injection, whereas other hormones (insulin-like growth factor I, glucagon, corticosterone) involved in the regulation of muscle protein synthesis were not altered significantly compared with control animals. The fractional rate of muscle protein synthesis, measured in vivo, was reduced significantly ( P < 0.05) in epitrochlearis (−46%), gastrocnemius (−41%), and soleus (−35%). The reduction in protein synthesis did not result from a reduced total RNA content but was associated with diminished translation efficiency. Analysis of ribosomal subunits revealed that the decreased translation efficiency resulted from an impairment in the initiation phase of protein synthesis. Diazoxide-induced insulin deficiency was associated with a dramatic decrease in eukaryotic initiation factor (eIF) 4G bound to eIF4E and a 2.5-fold increase in the amount of the eIF4E ⋅ 4E-binding protein 1 (BP1) complex. In contrast, diazoxide injection did not change either the relative amount of eIF4E present in gastrocnemius or its phosphorylation state. These results indicate that an acute insulin deficiency significantly decreases postprandial muscle protein synthesis by modulating the interaction between 4E-BP1, eIF4G, and eIF4E to control translation initiation.
Mechanisms involved in the regulation of key enzymes of cysteine metabolism in rat liver in vivo
Authors: Bella Deborah L. , Hirschberger Lawrence L. , Hosokawa Yu , Stipanuk Martha H.
Published: December 2017

Little is known about mechanisms of regulation of cysteine dioxygenase (CDO), γ-glutamylcysteine synthetase (GCS), and cysteine-sulfinate decarboxylase (CSDC) in response to diet. Enzyme activity and Western and Northern or dot blot analyses were conducted on liver samples from rats fed a basal low-protein diet or diets with graded levels of protein or methionine for 2 wk. Higher levels of CDO activity and CDO protein but not of CDO mRNA were observed in liver of rats fed methionine or protein-supplemented diets, indicating that CDO activity is regulated by changes in enzyme concentration. Lower concentrations of the heavy or catalytic subunit of GCS (GCS-HS) mRNA and protein, as well as a lower activity state of GCS-HS in rats fed methionine- or protein-supplemented diets, indicated that dietary regulation of GCS occurs by both pretranslational and posttranslational mechanisms. Lower CSDC activity, CSDC protein concentration, and CSDC mRNA concentration were found in rats fed the highest level of protein, and regulation appeared to involve changes in mRNA concentration. Regulation of key enzymes of cysteine metabolism in response to diet determines the use of cysteine for synthesis of its essential metabolites.
Serum leptin concentrations and their relation to metabolic abnormalities in human sepsis
Authors: Carlson G. L. , Saeed M. , Little R. A. , Irving M. H.
Published: December 2017

Circulating leptin concentrations are raised in animal models of inflammation and sepsis. The purpose of this study was to determine the effect of sepsis on serum leptin concentration in humans and to examine the relationship between leptin and the metabolic consequences of sepsis. Resting energy expenditure, insulin sensitivity, and fasting serum leptin, plasma insulin, and cortisol concentrations were measured in 20 subjects with intra-abdominal sepsis and 20 healthy control subjects, before and during a 2-h period of euglycemic hyperinsulinemia. Fasting serum leptin concentrations were similar in septic and control subjects. In simple regression analysis, serum leptin concentrations correlated significantly with percent body fat in both septic patients ( r = 0.64, P < 0.005) and healthy subjects ( r = 0.75, P < 0.0001). Multiple regression analyses additionally indicated that percent body fat, fasting plasma insulin, and plasma cortisol, but not sepsis, were significant and independent determinants of serum leptin concentration. No relationship between leptin and resting energy expenditure or insulin sensitivity was identifiable. A major metabolic role for leptin in human sepsis therefore appears unlikely.
Effect of calorie restriction on in vivo glucose metabolism by individual tissues in rats
Authors: Wetter Thomas J. , Gazdag Annie C. , Dean David J. , Cartee Gregory D.
Published: December 2017

We evaluated the effects of 8 mo of calorie restriction [CR: 60% of ad libitum (AL) food intake] on glucose uptake by 14 tissues in unanesthetized, adult (12 mo) F344×BN rats. Glucose metabolism was assessed by the 2-[3H]deoxyglucose tracer technique at 1500 or 2100. Despite an ∼60% decline in insulinemia with CR, plasma 2-[3H]deoxyglucose clearance for CR was greater than for AL at both times. A small, CR-related decrease in glucose metabolic index ([Formula: see text]) occurred only at 1500 in the spleen and heart, and this decrease was reversed at 2100. In some tissues (cerebellum, lung, kidney, soleus, and diaphragm),[Formula: see text] was unaffected by diet, regardless of time. In the other tissues (brown fat, 3 white fat pads, epitrochlearis, plantaris, and gastrocnemius),[Formula: see text] was higher or tended to be higher for CR vs. AL at one or both times. These findings indicate that 8 mo of CR did not cause a continuous reduction in in vivo glucose uptake by any tissue studied, and, in several insulin-sensitive tissues, glucose uptake was at times greater for CR vs. AL rats.
Prior exercise increases net hepatic glucose uptake during a glucose load
Authors: Galassetti Pietro , Coker Robert H. , Lacy Drury B. , Cherrington Alan D. , Wasserman David H.
Published: December 2017

The aim of these studies was to determine whether prior exercise enhances net hepatic glucose uptake (NHGU) during a glucose load. Sampling catheters (carotid artery, portal, hepatic, and iliac veins), infusion catheters (portal vein and vena cava), and Doppler flow probes (portal vein, hepatic and iliac arteries) were implanted. Exercise (150 min; n = 6) or rest ( n = 6) was followed by a 30-min control period and a 100-min experimental period (3.5 mg ⋅ kg−1⋅ min−1of glucose in portal vein and as needed in vena cava to clamp arterial blood glucose at ∼130 mg/dl). Somatostatin was infused, and insulin and glucagon were replaced intraportally at fourfold basal and basal rates, respectively. During experimental period the arterial-portal venous (a-pv) glucose gradient (mg/dl) was −18 ± 1 in sedentary and −19 ± 1 in exercised dogs. Arterial insulin and glucagon were similar in the two groups. Net hepatic glucose balance (mg ⋅ kg−1⋅ min−1) shifted from 1.9 ± 0.2 in control period to −1.8 ± 0.2 (negative rates represent net uptake) during experimental period in sedentary dogs (Δ3.7 ± 0.5); with prior exercise it shifted from 4.1 ± 0.3 ( P < 0.01 vs. sedentary) in control period to −3.2 ± 0.4 ( P < 0.05 vs. sedentary) during experimental period (Δ7.3 ± 0.7, P < 0.01 vs. sedentary). Net hindlimb glucose uptake (mg/min) was 4 ± 1 in sedentary animals in control period and 13 ± 2 during experimental period; in exercised animals it was 7 ± 1 in control period ( P < 0.01 vs. sedentary) and 32 ± 4 ( P < 0.01 vs. sedentary) during experimental period. As the total glucose infusion rate (mg ⋅ kg−1⋅ min−1) was 7 ± 1 in sedentary and 11 ± 1 in exercised dogs, ∼30% of the added glucose infusion due to prior exercise could be accounted for by the greater NHGU. In conclusion, when determinants of hepatic glucose uptake (insulin, glucagon, a-pv glucose gradient, glycemia) are controlled, prior exercise increases NHGU during a glucose load due to an effect that is intrinsic to the liver. Increased glucose disposal in the postexercise state is therefore due to an improved ability of both liver and muscle to take up glucose.
Insulin hypoglycemia and growth hormone secretion in sheep: a paradox revisited
Authors: Jaffe Craig A. , Huffman Bryan W. , Demott-Friberg Roberta
Published: December 2017

Although insulin-induced hypoglycemia is a potent stimulus for growth hormone (GH) secretion in humans, hypoglycemia was reported to suppress GH in sheep. We investigated whether GH suppression in sheep during insulin hypoglycemia resulted from the dose of insulin administered or the fed state of the animal. Saline or insulin (0.05, 0.2, 1.0, or 5.0 U/kg) intravenous boluses were administered to eight fasted ewes in a crossover experiment. In another experiment, four sheep were fed 2 h before intravenous administrations of either 0.2 or 5 U/kg of insulin. All doses of insulin resulted in comparable hypoglycemia, although the duration of hypoglycemia increased directly with insulin dose. Hypoglycemia in fasted animals stimulated GH secretion. The GH rise above baseline was inversely related to the insulin dose, and the insulin doses of 1 and 5 U/kg resulted in late suppression of GH below baseline concentrations. Insulin administration to fed animals caused an identical degree of hypoglycemia but no increase in GH. Insulin-hypoglycemia stimulates GH secretion in sheep in a manner similar to humans, and the response is dependent on both fed state and insulin dose.
Systemic resistance to the antilipolytic effect of insulin in black and white women with visceral obesity
Authors: Albu Jeanine B. , Curi Michael , Shur Meredith , Murphy Laura , Matthews Dwight E. , Pi-Sunyer F. Xavier
Published: December 2017

This study was designed to determine the role of visceral adipose tissue (VAT) accumulation in systemic fat metabolism and to compare this in black and white women who differ in their manifestations of upper body obesity. Systemic glycerol and free fatty acid (FFA) turnover rates (rates of appearance, Ra) were measured in the basal state and during a pancreatic euglycemic clamp in nondiabetic, premenopausal, obese black and white women with a wide range of VAT accumulation. The slopes of the regression equations predicting basal and insulin-suppressed RaGlycerol and RaFFA from VAT area, age, and fat mass or fat-free mass did not significantly differ between black and white women. VAT area was the best predictor of the %-suppressed RaGlycerol and RaFFA during the pancreatic clamp (partial r = 0.76, P < 0.0001 and partial r = 0.60, P < 0.05, respectively). Basal RaGlycerol, but not RaFFA, was lower in black than in white women ( P < 0.05). During the clamp, black women showed greater insulin suppression of RaGlycerol than of RaFFA ( P < 0.0001) and greater insulin suppression of RaGlycerol ( P < 0.05) but similar suppression of RaFFA compared with white women. These differences were independent of age, fat mass, or fat-free mass and were partly explained by a lower VAT in black women. Thus, in both races, VAT accumulation was associated with systemic resistance to the antilipolytic effect of insulin and, in obese black women, systemic lipolysis measured as glycerol turnover rate was more responsive to insulin suppression than were systemic FFA turnover rates.
Lower recovery of muscle protein lost during starvation in old rats despite a stimulation of protein synthesis
Authors: Mosoni L. , Malmezat T. , Valluy M. C. , Houlier M. L. , Attaix D. , Mirand P. Patureau
Published: December 2017

Sarcopenia could result from the inability of an older individual to recover muscle lost during catabolic periods. To test this hypothesis, we compared the capacity of 5-day-refed 12- and 24-mo-old rats to recover muscle mass lost after 10 days without food. We measured gastrocnemius and liver protein synthesis with the flooding-dose method and also measured nitrogen balance, 3-methylhistidine excretion, and the gene expression of components of proteolytic pathways in muscle comparing fed, starved, and refed rats at each age. We show that 24-mo-old rats had an altered capacity to recover muscle proteins. Muscle protein synthesis, inhibited during starvation, returned to control values during refeeding in both age groups. The lower recovery in 24-mo-old rats was related to a lack of inhibition of muscle proteolysis during refeeding. The level of gene expression of components of the proteolytic pathways did not account for the variations in muscle proteolysis at both ages. In conclusion, this study highlights the role of muscle proteolysis in the lower recovery of muscle protein mass lost during catabolic periods.
The head arterial glucose level is not the reference site for generation of the portal signal in conscious dogs
Authors: Hsieh Po-Shiuan , Moore Mary Courtney , Marshall Bess , Pagliassotti Michael J. , Shay Brian , Szurkus Dennis , Neal Doss W. , Cherrington Alan D.
Published: December 2017

Experiments were performed on twelve 42-h-fasted, conscious dogs to determine whether the head arterial glucose level is used as a reference standard for comparison with the portal glucose level in bringing about the stimulatory effect of portal glucose delivery on net hepatic glucose uptake (NHGU). Each experiment consisted of an 80-min equilibration, a 40-min control, and two 90-min test periods. After the control period, somatostatin was given along with insulin (7.2 pmol ⋅ kg−1⋅ min−1; 3.5-fold increase) and glucagon (0.6 ng ⋅ kg−1⋅ min−1; basal) intraportally. Glucose was infused intraportally (22.2 μmol ⋅ kg−1⋅ min−1) and peripherally as needed to double the hepatic glucose load. In one test period, glucose was infused into both vertebral and carotid arteries (HEADG; 22.2 ± 0.8 μmol ⋅ kg−1⋅ min−1); in the other test period, saline was infused into the head arteries (HEADS). One-half of the dogs received HEADGfirst. When all dogs are considered, the blood arterial-portal glucose gradients (−0.52 ± 0.07 vs. −0.49 ± 0.03 mM) and the hepatic glucose loads (339 ± 14 vs. 334 ± 20 μmol ⋅ kg−1⋅ min−1) were similar in HEADGand HEADS. NHGU was 24.1 ± 3.8 and 25.1 ± 4.6 μmol ⋅ kg−1⋅ min−1, and nonhepatic glucose uptake was 46.1 ± 4.2 and 48.8 ± 7.0 μmol ⋅ kg−1⋅ min−1in HEADGand HEADS, respectively. The head arterial glucose level is not the reference standard used for comparison with the portal glucose level in the generation of the portal signal.
Inverse alterations of BCKA dehydrogenase activity in cardiac and skeletal muscles of diabetic rats
Authors: Lombardo Yolanda B. , Serdikoff Cynthia , Thamotharan Manikkavasagar , Paul Harbhajan S. , Adibi Siamak A.
Published: December 2017

Rat cardiac and skeletal muscles, which have been used as model tissues for studies of regulation of branched-chain α-keto acid (BCKA) oxidation, vary greatly in the activity state of their BCKA dehydrogenase. In the present experiment, we have investigated whether they also vary in response of their BCKA dehydrogenase to a metabolic alteration such as diabetes and, if so, to investigate the mechanism that underlies the difference. Diabetes was produced by depriving streptozotocin-treated rats of insulin administration for 96 h. The investigation of BCKA dehydrogenase in the skeletal muscle (gastrocnemius) showed that diabetes 1) increased its activity, 2) increased the protein and gene expressions of all of its subunits (E1α, E1β, E2), 3) increased its activity state, 4) decreased the rate of its inactivation, and 5) decreased the protein expression of its associated kinase (BCKAD kinase) without affecting its gene expression. In sharp contrast, the investigation of BCKA dehydrogenase in the cardiac muscle showed that diabetes 1) decreased its activity, 2) had no effect on either protein or gene expression of any of its subunits, 3) decreased its activity state, 4) increased its rate of inactivation, and 5) increased both the protein and gene expressions of its associated kinase. In conclusion, our data suggest that, in diabetes, the protein expression of BCKAD kinase is downregulated posttranscriptionally in the skeletal muscle, whereas it is upregulated pretranslationally in the cardiac muscle, causing inverse alterations of BCKA dehydrogenase activity in these muscles.
Ethnicity affects the postprandial regulation of glycogenolysis
Authors: Balasubramanyam Ashok , McKay Siripoom , Nadkarni Prashant , Rajan Arun S. , Garza Armandina , Pavlik Valory , Herd J. Alan , Jahoor Farook , Reeds Peter J.
Published: December 2017

We investigated the effect of nutrient intake on glucose metabolism in normal Mexican-Americans ( n = 6) and European-Americans ( n = 6). Subjects were studied after an 18-h fast and after 5–6 h of ingestion of hourly meals that supplied 6.35 or 12.75 μmol glucose ⋅ kg−1⋅ min−1. Endogenous glucose production (EGP), gluconeogenesis (GNG), and glycogenolysis (GLY) were estimated by mass isotopomer analysis with [U-13C]glucose infusions. Fasting EGP, GNG, and GLY did not differ between the groups. Food ingestion lowered the molar rate of GNG by only 31%. However, while consuming the lower quantity of nutrients, Mexican-Americans had higher plasma glucose ( P < 0.05), a 39% higher rate of EGP ( P< 0.05), and a 68% ( P < 0.025) higher rate of GLY than the European-Americans. At the higher intake, EGP and GLY were suppressed completely in both groups. There was a linear relationship between insulin concentrations, EGP, and GLY in both groups, but the slope of the line was significantly ( P < 0.05) greater in the European-Americans. We conclude that the sensitivity of GLY to nutrient intake differs between ethnic groups and that this may play a role in the increased predisposition of Mexican-Americans to type II diabetes.
Glutamate ingestion: the plasma and muscle free amino acid pools of resting humans
Authors: Graham T. E. , Sgro V. , Friars D. , Gibala M. J.
Published: December 2017

Monosodium glutamate (MSG) ingestion is known to increase plasma glutamate concentration, and MSG infusion stimulates insulin secretion. We investigated the impact of MSG ingestion on both the plasma and intramuscular amino acid pools. Nine postprandial adults ingested MSG (150 mg/kg) and rested for 105 min. Venous blood was sampled preingestion and then every 15 min; vastus lateralis muscle biopsies were taken preingestion and at 45, 75, and 105 min postingestion. Venous plasma glutamate and aspartate concentrations increased ( P ≤ 0.05) ∼700–800 and 300–400%, respectively, after 30–45 min. Although several other plasma amino acids increased modestly, the rise in glutamate accounted for ∼80% of the increase in total plasma amino acids. In addition, plasma insulin increased threefold after 15 min; this occurred before a significant increase in plasma glutamate, indicating a feed-forward stimulation from the gastrointestinal tract. The intramuscular amino acid pool was remarkably constant, with only glutamate increasing ( P ≤ 0.05) by 3.56 mmol/kg dry wt. By 105 min, the plasma and muscle amino acids had returned to resting concentrations. This increase in muscle glutamate concentration could account for ∼40% of the MSG ingested; we propose that resting skeletal muscle is a major sink for the glutamate and metabolizes it to aspartate.
Integrative physiology of splanchnic glutamine and ammonium metabolism
Authors: Yang Dawei , Hazey Jeffrey W. , David France , Singh Jittendra , Rivchum Ryan , Streem Jason M. , Halperin Mitchell L. , Brunengraber Henri
Published: December 2017

The substrates for hepatic ureagenesis are equimolar amounts of ammonium and aspartate. The study design mimics conditions in which the liver receives more [Formula: see text]than aspartate precursors (very low-protein diet). Fasted dogs, fitted acutely with transhepatic catheters, were infused with a tracer amount of 15NH4Cl. From arteriovenous differences, the major [Formula: see text] precursor for hepatic ureagenesis was via deamidation of glutamine in the portal drainage system (rather than in the liver), because there was a 1:1 stoichiometry between glutamine disappearance and[Formula: see text] appearance, and the amide (but not the amine) nitrogen of glutamine supplied the 15N added to the portal venous [Formula: see text] pool. The liver extracted all this [Formula: see text] from glutamine deamidation plus an additional amount in a single pass, suggesting that there was an activator of hepatic ureagenesis. The other major source of nitrogen extracted by the liver was [14N]alanine. Because alanine was not produced in the portal venous system, we speculate that it was derived ultimately from proteins in peripheral tissues.