bluuebunny/crossref_metadata_2025 huggingface dataset:
Hyperinsulinemia compensates for infection-induced impairment in net hepatic glucose uptake during TPN
Authors: Donmoyer Christine M. , Chen Sheng-Song , Hande Scott A. , Lacy D. Brooks , Ejiofor Joseph , McGuinness Owen P.
Published: December 2017

In animals receiving total parenteral nutrition (TPN), infection impairs net hepatic glucose uptake (NHGU) by 40% and induces mild hyperinsulinemia. In the normal animal, the majority of the glucose taken up by the liver is diverted to lactate, but in the infected state, lactate release is curtailed. Because of the hyperinsulinemia and reduced NHGU, more glucose is utilized by peripheral tissues. Our aims were to determine the role of infection-induced hyperinsulinemia in 1) limiting the fall in NHGU and hepatic lactate release and 2) increasing the proportion of glucose disposed of by peripheral tissues. Chronically catheterized dogs received TPN for 5 days via the inferior vena cava. On day 3, a fibrin clot with a nonlethal dose of E. coli was placed into the peritoneal cavity; sham dogs received a sterile clot. On day 5, somatostatin was infused to prevent endogenous pancreatic hormone secretion, and insulin and glucagon were replaced at rates matching incoming hormone concentrations observed previously in sham or infected dogs. The TPN-derived glucose infusion was adjusted to maintain a constant arterial plasma glucose level of ∼120 mg/dl. after a basal blood sampling period, the insulin infusion rate was either maintained constant (infected time control, Hi-Ins, n = 6; sham time control, Sham, n = 6) or decreased (infected + reduced insulin, Lo-Ins; n = 6) for 180 min to levels seen in noninfected dogs (from 23 ± 2 to 12 ± 1 μU/ml). Reduction of insulin to noninfected levels decreased NHGU by 1.4 ± 0.5 mg · kg−1· min−1( P < 0.05) and nonhepatic glucose utilization by 4.8 ± 0.8 mg · kg−1· min−1( P < 0.01). The fall in NHGU was caused by a decline in HGU (Δ−0.6 ± 0.4 mg · kg−1· min−1) and a concomitant increase in hepatic glucose production (HGP, Δ0.8 ± 0.5 mg · kg−1· min−1); net hepatic lactate release was not altered. Hyperinsulinemia that accompanies infection 1) primarily diverts glucose carbon to peripheral tissues, 2) limits the fall in NHGU by enhancing HGU and suppressing HGP, and 3) does not enhance hepatic lactate release, thus favoring hepatic glucose storage. Compensatory hyperinsulinemia plays a critical role in facilitating hepatic and peripheral glucose disposal during an infection.
Amino acids regulate skeletal muscle PHAS-I and p70 S6-kinase phosphorylation independently of insulin
Authors: Long W. , Saffer L. , Wei L. , Barrett E. J.
Published: December 2017

Refeeding reverses the muscle protein loss seen with fasting. The physiological regulators and cellular control sites responsible for this reversal are incompletely defined. Phosphorylation of phosphorylated heat-acid stabled protein (PHAS-I) frees eukaryotic initiation factor 4E (eIF4E) and stimulates protein synthesis by accelerating translation initiation. Phosphorylation of p70 S6-kinase (p70S6k) is thought to be involved in the regulation of the synthesis of some ribosomsal proteins and other selected proteins with polypyrimidine clusters near the transcription start site. We examined whether phosphorylation of PHAS-I and p70S6k was increased by feeding and determined the separate effects of insulin and amino acids on PHAS-I and p70S6k phosphorylation in rat skeletal muscle in vivo. Muscle was obtained from rats fed ad libitum or fasted overnight ( n = 5 each). Other fasted rats were infused with insulin (3 μU · min−1 · kg−1, euglycemic clamp), amino acids, or the two combined. Gastrocnemius was freeze-clamped, and PHAS-I and p70S6k phosphorylation was measured by quantifying the several phosphorylated forms of these proteins seen on Western blots. We observed that feeding increased phosphorylation of both PHAS-I and p70S6k ( P < 0.05). Infusion of amino acids alone reproduced the effect of feeding. Physiological hyperinsulinemia increased p70S6K ( P< 0.05) but not PHAS-I phosphorylation ( P = 0.98). Addition of insulin to amino acid infusion was no more effective than amino acids alone in promoting PHAS-I and p70S6kphosphorylation. We conclude that amino acid infusion alone enhances the activation of the protein synthetic pathways in vivo in rat skeletal muscle. This effect is not dependent on increases in plasma insulin and simulates the activation of protein synthesis that accompanies normal feeding.
Effect of endurance training on lipid metabolism in women: a potential role for PPARα in the metabolic response to training
Authors: Horowitz Jeffrey F. , Leone Teresa C. , Feng Weqing , Kelly Daniel P. , Klein Samuel
Published: December 2017

Endurance training increases fatty acid oxidation (FAO) and skeletal muscle oxidative capacity. However, the source of the additional fat and the mechanisms for increasing FAO capacity in muscle are not clear. We measured whole body and regional lipolytic activity and whole body and plasma FAO in six lean women during 90 min of bicycling exercise (50% pretraining peak O2consumption) before and after 12 wk of endurance training. We also assessed skeletal muscle content of peroxisome proliferator-activated receptor-α (PPARα) and its target proteins that regulate FAO [medium-chain and very long chain acyl-CoA dehydrogenase (MCAD and VLCAD)]. Despite a 25% increase in whole body FAO during exercise after training ( P < 0.05), training did not alter regional adipose tissue lipolysis (abdominal: 0.56 ± 0.26 and 0.57 ± 0.10 μmol · 100 g−1· min−1; femoral: 0.13 ± 0.07 and 0.09 ± 0.02 μmol · 100 g−1· min−1), whole body palmitate rate of appearance in plasma (168 ± 18 and 150 ± 25 μmol/min), and plasma FAO (554 ± 61 and 601 ± 45 μmol/min). However, training doubled the levels of muscle PPARα, MCAD, and VLCAD. We conclude that training increases the use of nonplasma fatty acids and may enhance skeletal muscle oxidative capacity by PPARα regulation of gene expression.
Osmotic and glutamate receptor regulation of c-Jun NH2-terminal protein kinase in neuroendocrine cells
Authors: Meeker Rick , Fernandes Alda
Published: December 2017

Expression of a c-Jun NH2-terminal protein kinase (JNK), also known as stress-activated protein kinase (SAPK) in rodents, has been implicated in the ability of cells to respond to a variety of stressors. In nonmammalian cells, JNK participates in the regulation of cell volume in response to hyperosmotic stress. To explore the possibility that JNK may participate in the transduction of osmotic information in mammals, we evaluated the expression of JNK immunoreactivity in neuroendocrine cells of the supraoptic nucleus. Low basal expression of JNK-2 (SAPK-α) and JNK-3 (SAPK-β) was seen in vivo and in vitro. During water deprivation, JNK-2 increased in the supraoptic nucleus but not in the cortex. Osmotic or glutamate receptor stimulation in vitro also resulted in an increase in JNK-2 that was tetrodotoxin (TTX) insensitive and paralleled by increased nuclear phospho-c-Jun immunoreactivity. A TTX-sensitive increase in JNK-3 was seen in smaller neurons. Thus different JNK pathways may mediate individual cellular responses to osmotic stress, with JNK-2 linked to osmotic and glutamate receptor stimulation in magnocellular neuroendocrine cells.
Effect of CCK pretreatment on the CCK sensitivity of rat polymodal gastric vagal afferent in vitro
Authors: Wei Jen Yu , Wang Yu Hua
Published: December 2017

To prevent the blood-borne interference and reflex actions via neighboring organs and the central nervous system, the study was conducted in an in vitro isolated stomach-gastric vagus nerve preparation obtained from overnight-fasted, urethan-anesthetized rats. Afferent unit action potentials were recorded from the gastric branch of the vagus nerve. The left gastric artery was catheterized for intra-arterial injection. In vitro we found that 1) 55/70 gastric vagal afferents (GVAs) were polymodal, responding to CCK-8 and mechanical stimuli, 13 were mechanoreceptive, and 2 were CCK-responsive; 2) sequential or randomized intra-arterial injections of CCK-8 (0.1–200 pmol) dose-dependently increased firing rate and reached the peak rate at 100 pmol; 3) the action was suppressed by CCK-A (Devazepide) but not by CCK-B (L-365,260) receptor antagonist; 4) neither antagonist blocked the mechanosensitivity of GVA fibers. These results are consistent with corresponding in vivo well-documented findings. Histological data indicate that the layered structure of the stomach wall was preserved in vitro for 6–8 h. Based on these results, it seems reasonable to use the in vitro preparation for conducting a study that is usually difficult to be performed in vivo. For instance, because there was no blood supply in vitro, the composition of the interstitial fluid, i.e., the ambient nerve terminals, can be better controlled and influenced by intra-arterial injection of a defined solution. Here we report that acutely changing the ambient CCK level by a conditioning stimulus (a preceding intra-arterial injection of increasing doses of CCK-8) reduced the CCK sensitivity of GVA terminals to a subsequent test stimulus (a constant dose of CCK-8 intra-arterial injection).
Effect of prolactin on sodium iodide symporter expression in mouse mammary gland explants
Authors: Rillema James A. , Yu Ting Xi , Jhiang Sissy M.
Published: December 2017

Iodide accumulates in milk at a concentration that is more than an order of magnitude higher than the iodide concentration in maternal plasma. In earlier studies from our laboratory, we have shown that prolactin (PRL) enhances iodide accumulation by two- to threefold in cultured mammary tissues taken from pregnant mice. In the present studies, we demonstrate via Western blotting techniques that prolactin elevates the quantity of the sodium iodide symporter (NIS) in cultured mouse mammary tissues. In time-course studies, the onset of the PRL effect of NIS accumulation was found to be between 4 and 16 h after addition of PRL to the explants. The lowest PRL concentration that elicited a significant response was 1 ng/ml, and a maximum effect was elicited with PRL concentrations >100 ng/ml. Actinomycin D, cycloheximide, and thiocyanate abolished the PRL effect on NIS accumulation, whereas perchlorate was without effect. These studies suggest that the PRL stimulation of iodide accumulation in milk is mediated, at least in part, by the PRL stimulation of NIS accumulation in mammary gland tissues. These studies further demonstrate that the PRL effect on NIS accumulation occurs via an RNA protein synthesis-dependent mechanism.
Effects of mental stress on insulin-mediated glucose metabolism and energy expenditure in lean and obese women
Authors: Seematter G. , Guenat E. , Schneiter P. , Cayeux C. , Jéquier E. , Tappy L.
Published: December 2017

The effects of the sympathetic activation elicited by a mental stress on insulin sensitivity and energy expenditure (V˙o 2) were studied in 11 lean and 8 obese women during a hyperinsulinemic-euglycemic clamp. Six lean women were restudied under nonselective β-adrenergic blockade with propranolol to determine the role of β-adrenoceptors in the metabolic response to mental stress. In lean women, mental stress increasedV˙o 2 by 20%, whole body glucose utilization ([6,6-2H2]glucose) by 34%, and cardiac index (thoracic bioimpedance) by 25%, whereas systemic vascular resistance decreased by 24%. In obese women, mental stress increased energy expenditure as in lean subjects, but it neither stimulated glucose uptake nor decreased systemic vascular resistance. In the six lean women who were restudied under propranolol, the rise inV˙o 2, glucose uptake, and cardiac output and the decrease in systemic vascular resistance during mental stress were all abolished. It is concluded that 1) in lean subjects, mental stress stimulates glucose uptake and energy expenditure and produces vasodilation; activation of β-adrenoceptors is involved in these responses; and 2) in obese patients, the effects of mental stress on glucose uptake and systemic vascular resistance, but not on energy expenditure, are blunted.
Cyclic mechanical distension regulates renin gene transcription in As4.1 cells
Authors: Ryan Michael J. , Black Thomas A. , Gross Kenneth W. , Hajduczok George
Published: December 2017

The renin-producing and -secreting juxtaglomerular (JG) cells are thought to function as the baroreceptor of the kidney. The mechanism by which changes in pressure, or mechanical force, regulate renin at the molecular level has not been elucidated. The renin gene-expressing and -secreting clonal cell line As4.1 was derived from transgene-targeted oncogenesis in mice and was used as a cellular model for JG cells. As4.1 cells subjected to cyclic mechanical distension for a period of 24 h at various frequencies (0.05 or 0.5 Hz) and magnitudes (12 or 24% elongation) were analyzed via Northern analysis for renin mRNA levels. Results indicate that renin gene expression is decreased by 50–85% and returns to basal levels after a 24-h recovery period. Renin gene expression was attenuated independently of elevated cell growth or changes in renin message decay, suggesting that renin gene transcription is directly modulated by mechanical distension. Transient transfection of As4.1 cells with renin 5′ flanking sequence-luciferase reporter gene constructs confirmed the role of mechanical stimulation in regulating renin gene transcription. A 43% inhibition of luciferase activity, by stretch, was observed in cells transfected with a 4,000 base pair 5′ flanking sequence to the renin proximal promoter. These results demonstrate for the first time that changes in mechanical force can result in the regulation of renin gene transcription and thus provide further insight into the baroreceptor properties of renin-expressing cells.
GLUT-3 expression in human skeletal muscle
Authors: Stuart Charles A. , Wen Gary , Peng Bi-Hung , Popov Vsevolod L. , Hudnall S. David , Campbell Gerald A.
Published: December 2017

Muscle biopsy homogenates contain GLUT-3 mRNA and protein. Before these studies, it was unclear where GLUT-3 was located in muscle tissue. In situ hybridization using a midmolecule probe demonstrated GLUT-3 within all muscle fibers. Fluorescent-tagged antibody reacting with affinity-purified antibody directed at the carboxy-terminus demonstrated GLUT-3 protein in all fibers. Slow-twitch muscle fibers, identified by NADH-tetrazolium reductase staining, possessed more GLUT-3 protein than fast-twitch fibers. Electron microscopy using affinity-purified primary antibody and gold particle-tagged second antibody showed that the majority of GLUT-3 was in association with triads and transverse tubules inside the fiber. Strong GLUT-3 signals were seen in association with the few nerves that traversed muscle sections. Electron microscopic evaluation of human peripheral nerve demonstrated GLUT-3 within the axon, with many of the particles related to mitochondria. GLUT-3 protein was found in myelin but not in Schwann cells. GLUT-1 protein was not present in nerve cells, axons, myelin, or Schwann cells but was seen at the surface of the peripheral nerve in the perineurium. These studies demonstrated that GLUT-3 mRNA and protein are expressed throughout normal human skeletal muscle, but the protein is predominantly found in the triads of slow-twitch muscle fibers.
Measurement of skin protein breakdown in a rat model
Authors: Volpi Elena , Jeschke Marc G. , Herndon David N. , Wolfe Robert R.
Published: December 2017

Whereas skin protein synthesis can be measured with different approaches, no method potentially applicable in humans is available for measurement of skin protein breakdown. To that end, we measured mixed skin fractional protein breakdown (FBR) in a rat model by use of a stable isotope method (tracee release method) originally developed to measure muscle protein breakdown. Skin mixed protein and collagen fractional synthesis rates (FSR) were also measured. A primed continuous infusion ofl-[ ring-2H5]phenylalanine and α-[5,5,5-2H3]ketoisocaproate (KIC) was given for 6 h. Arterial and skin phenylalanine and leucine free enrichments were measured at plateau (5–6 h) and during the decay that followed after the infusion was stopped. Skin FBR (%/h) was 0.260 ± 0.011 with phenylalanine and 0.201 ± 0.032 with KIC/leucine [ P = not significant (NS)]. Mixed skin FSR (%/h) was 0.169 ± 0.055 with phenylalanine and 0.146 ± 0.020 with KIC/leucine ( P = NS). Collagen FSR was 0.124 ± 0.023%/h ( P = NS vs. mixed protein FSR). The tracee release method is a sensitive method for measurement of skin protein breakdown; however, given the high intersubject variability of FSR, the calculation of skin net balance is not advisable.
Augmentation of basal insulin release from rat islets by preexposure to a high concentration of glucose
Authors: Fujimoto Shimpei , Tsuura Yoshiyuki , Ishida Hitoshi , Tsuji Kazuo , Mukai Eri , Kajikawa Mariko , Hamamoto Yoshiyuki , Takeda Tomomi , Yamada Yuichiro , Seino Yutaka
Published: December 2017

We have found that preexposure to an elevated concentration of glucose reversibly induces an enhancement of basal insulin release from rat pancreatic islets dependent on glucose metabolism. This basal insulin release augmented by priming was not suppressed by reduction of the intracellular ATP or Ca2+concentration, because even in the absence of ATP at low Ca2+, the augmentation was not abolished from primed electrically permeabilized islets. Moreover, it was not inhibited by an α-adrenergic antagonist, clonidine. A threshold level of GTP is required to induce these effects, because together with adenine, mycophenolic acid, a cytosolic GTP synthesis inhibitor, completely abolished the enhancement of basal insulin release due to the glucose-induced priming without affecting the glucose-induced increment in ATP content and ATP-to-ADP ratio. In addition, a GDP analog significantly suppressed the enhanced insulin release due to priming from permeabilized islets in the absence of ATP at low Ca2+, suggesting that the GTP-sensitive site may play a role in the augmentation of basal insulin release due to the glucose-induced priming effect.
Glucose-stimulated insulin secretion suppresses hepatic triglyceride-rich lipoprotein and apoB production
Authors: Chirieac Doru V. , Chirieac Lucian R. , Corsetti James P. , Cianci Joanne , Sparks Charles E. , Sparks Janet D.
Published: December 2017

The current study assessed in vivo the effect of insulin on triglyceride-rich lipoprotein (TRL) production by rat liver. Hepatic triglyceride and apolipoprotein B (apoB) production were measured in anesthetized, fasted rats injected intravenously with Triton WR-1339 (400 mg/kg). After intravascular catabolism was blocked by detergent treatment, glucose (500 mg/kg) was injected to elicit insulin secretion, and serum triglyceride and apoB accumulation were monitored over the next 3 h. In glucose-injected rats, triglyceride secretion averaged 22.5 ± 2.1 μg · ml−1· min−1, which was significantly less by 30% than that observed in saline-injected rats, which averaged 32.1 ± 1.4 μg · ml−1· min−1. ApoB secretion was also significantly reduced by 66% in glucose-injected rats. ApoB immunoblotting indicated that both B100 and B48 production were significantly reduced after glucose injection. Results support the conclusion that insulin acts in vivo to suppress hepatic very low density lipoprotein (VLDL) triglyceride and apoB secretion and strengthen the concept of a regulatory role for insulin in VLDL metabolism postprandially.
Impaired myocardial protein synthesis induced by acute alcohol intoxication is associated with changes in eIF4F
Authors: Lang Charles H. , Frost Robert A. , Kumar Vinayshree , Vary Thomas C.
Published: December 2017

The purpose of the present study was to examine potential mechanisms for the known inhibitory effect of acute alcohol exposure on myocardial protein synthesis. Rats were injected intraperitoneally with either ethanol (75 mmol/kg) or saline, and protein synthesis was measured in vivo 2.5 h thereafter by use of the flooding-dosel-[3H]phenylalanine technique. Rates of myocardial protein synthesis and translational efficiency in alcohol-treated rats were decreased compared with control values. Free (nonpolysome bound) 40S and 60S ribosomal subunits were increased 50% after alcohol treatment, indicating an impaired peptide-chain initiation. To identify mechanisms responsible for this impairment, several eukaryotic initiation factors (eIF) were analyzed. Acute alcohol intoxication did not significantly alter the myocardial content of eIF2α or eIF2Bɛ, the extent of eIF2α phosphorylation, or the activity of eIF2B. Acute alcohol exposure increased the binding of 4E-binding protein 1 (4E-BP1) to eIF4E (55%), diminished the amount of eIF4E bound to eIF4G (70%), reduced the amount of 4E-BP1 in the phosphorylated γ-form (40%), and decreased the phosphorylation of p70S6 kinase and the ribosomal protein S6. There was no significant difference in either the plasma insulin-like growth factor (IGF) I concentration (total or free) or expression of IGF-I or IGF-II mRNA in heart between the two groups. These data suggest that the acute alcohol-induced impairment in myocardial protein synthesis results, in part, from an inhibition in peptide-chain initiation, which is associated with marked changes in eIF4E availability and p70S6 kinase phosphorylation but is independent of changes in the eIF2/2B system and IGFs.
Retinoic acid and host-pathogen interactions: effects on inducible nitric oxide synthase in vivo
Authors: Devaux Yvan , Grosjean Sandrine , Seguin Carole , David Chantal , Dousset Brigitte , Zannad Faiez , Meistelman Claude , De Talancé Nicole , Mertes Paul-Michel , Ungureanu-Longrois Dan
Published: December 2017

Vitamin A and its metabolite retinoic acid modulate the host response to pathogens through poorly characterized mechanisms. In vitro studies have suggested that retinoic acid decreases inducible NO synthase (NOS2, or iNOS) expression, a component of innate immunity, in several cell types stimulated with lipopolysaccharide (LPS) or cytokines. This study investigated the effect of retinoic acid on LPS-stimulated NOS2 expression in vivo. Wistar-Kyoto rats received all- trans retinoic acid (RA, 10 mg/kg) or vehicle intraperitoneally daily for 5 days followed by LPS (4 mg/kg) or saline intraperitoneally and were killed 6 h later. NOS2 activation was estimated by mRNA (RT-PCR) and protein (Western-blot) expression and plasma nitrate/nitrite accumulation. In sharp contrast to previous in vitro study reports, RA significantly enhanced NOS2 mRNA, protein expression, and plasma nitrate/nitrite concentration in LPS-injected rats but not in saline-injected rats. This was associated with increased expression of interleukin-2, interferon (IFN)-γ and IFN regulatory factor-1 mRNAs in several organs and increased IFN-γ plasma concentration. RA significantly increased mortality in LPS-injected rats. The NOS inhibitor aminoguanidine (50 mg/kg before LPS injection) significantly attenuated the RA-mediated increase in mortality. These results demonstrate for the first time that RA supplementation in vivo enhances activation of the LPS-triggered NOS2 pathway.
Immobilization depresses insulin signaling in skeletal muscle
Authors: Hirose Munetaka , Kaneki Masao , Sugita Hiroki , Yasuhara Shingo , Martyn J. A. Jeevendra
Published: December 2017

Prolonged immobilization depresses insulin-induced glucose transport in skeletal muscle and leads to a catabolic state in the affected areas, with resultant muscle wasting. To elucidate the altered intracellular mechanisms involved in the insulin resistance, we examined insulin-stimulated tyrosine phosphorylation of the insulin receptor β-subunit (IR-β) and insulin receptor substrate (IRS)-1 and activation of its further downstream molecule, phosphatidylinositol 3-kinase (PI 3-K), after unilateral hindlimb immobilization in the rat. The contralateral hindlimb served as control. After 7 days of immobilization of the rat, insulin was injected into the portal vein, and tibialis anterior muscles on both sides were extracted. Immobilization reduced insulin-stimulated tyrosine phosphorylation of IR-β and IRS-1. Insulin-stimulated binding of IRS-1 to p85, the regulatory subunit of PI 3-K, and IRS-1-associated PI 3-K activity were also decreased in the immobilized hindlimb. Although IR-β and p85 protein levels were unchanged, IRS-1 protein expression was downregulated by immobilization. Thus prolonged immobilization may cause depression of insulin-stimulated glucose transport in skeletal muscle by altering insulin action at multiple points, including the tyrosine phosphorylation, protein expression, and activation of essential components of insulin signaling pathways.
Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes
Authors: Goedecke Julia H. , Gibson Alan St Clair , Grobler Liesl , Collins Malcolm , Noakes Timothy D. , Lambert Estelle V.
Published: December 2017

We examined the variability and determinants of the respiratory exchange ratio (RER) at rest and during exercise in 61 trained cyclists. Fasting (10–12 h) RER was measured at rest and during exercise at 25, 50, and 70% of peak power output (Wpeak), during which blood samples were drawn for [lactate] and [free fatty acid] ([FFA]). Before these measurements, training volume, dietary intake and muscle fiber composition, [substrate], and enzyme activities were determined. There was large interindividual variability in resting RER (0.718–0.927) that persisted during exercise of increasing intensity. The major determinants of resting RER included muscle glycogen content, training volume, proportion of type 1 fibers, [FFA] and [lactate], and %dietary fat intake (adjusted r2= 0.59, P < 0.001). Except for muscle fiber composition, these variables also predicted RER at 25, 50, and 70% Wpeakto different extents. The key determinant at 25% Wpeakwas blood-borne [substrate], at 50% was muscle [substrate] and glycolytic enzyme activities, and at 70% was [lactate]. Resting RER was also a significant determinant of RER at 25 ( r = 0.60) and 50% ( r = 0.44) Wpeak.
Acyl-CoAs are functionally channeled in liver: potential role of acyl-CoA synthetase
Authors: Muoio Deborah M. , Lewin Tal M. , Wiedmer Petra , Coleman Rosalind A.
Published: December 2017

Acyl-CoA synthetase (ACS) catalyzes the activation of long-chain fatty acids to acyl-CoAs, which can be metabolized to form CO2, triacylglycerol (TAG), phospholipids (PL), and cholesteryl esters (CE). To determine whether inhibiting ACS affects these pathways differently, we incubated rat hepatocytes with [14C]oleate and the ACS inhibitor triacsin C. Triacsin inhibited TAG synthesis 70% in hepatocytes from fed rats and 40% in starved rats, but it had little effect on oleate incorporation into CE, PL, or β-oxidation end products. Triacsin blocked [3H]glycerol incorporation into TAG and PL 33 and 25% more than it blocked [14C]oleate incorporation, suggesting greater inhibition of de novo TAG synthesis than reacylation. Triacsin did not affect oxidation of prelabeled intracellular lipid. ACS1 protein was abundant in liver microsomes but virtually undetectable in mitochondria. Refeeding increased microsomal ACS1 protein 89% but did not affect specific activity. Triacsin inhibited ACS specific activity in microsomes more from fed than from starved rats. These data suggest that ACS isozymes may be functionally linked to specific metabolic pathways and that ACS1 is not associated with β-oxidation in liver.
Prolonged exercise after diuretic-induced hypohydration: effects on substrate turnover and oxidation
Authors: Roy B. D. , Green H. J. , Burnett M.
Published: December 2017

To determine the influence of a diuretic-induced reduction in plasma volume (PV) on substrate turnover and oxidation, 10 healthy young males were studied during 60 min of cycling exercise at 61% peak oxygen uptake on two separate occasions ≥1 wk apart. Exercise was performed under control conditions (CON; placebo), and after 4 days of diuretic administration (DIU; Novotriamazide; 100 mg triamterene and 50 mg hydrochlorothiazide). DIU resulted in a calculated reduction of PV by 14.6 ± 3.3% ( P < 0.05). Rates of glucose appearance (Ra) and disappearance (Rd) and glycerol Rawere determined by using primed constant infusions of [6,6-2H]glucose and [2H5]glycerol, respectively. No differences in oxygen uptake during exercise were observed between trials. Main effects for condition ( P < 0.05) were observed for plasma glucose and glycerol, such that the values observed for DIU were higher than for CON. No differences were observed in plasma lactate and serum free fatty acid concentrations either at rest or during exercise. Hypohydration led to lower ( P < 0.05) glucose Raand Rdat rest and at 15 and 30 min of exercise, but by 60 min, the effects were reversed ( P < 0.05). Hypohydration had no effect on rates of whole body lipolysis or total carbohydrate or fat oxidation. A main effect for condition ( P < 0.05) was observed for plasma glucagon concentrations such that larger values were observed for DIU than for CON. A similar decline in plasma insulin occurred with exercise in both conditions. These results indicate that diuretic-induced reductions in PV decreases glucose kinetics during moderate-intensity dynamic exercise in the absence of changes in total carbohydrate and fat oxidation. The specific effect on glucose kinetics depends on the duration of the exercise.
Impairment of endothelial nitric oxide production by acute glucose overload
Authors: Kimura Chiwaka , Oike Masahiro , Koyama Tetsuya , Ito Yushi
Published: December 2017

We examined the effects of acute glucose overload (pretreatment for 3 h with 23 mM d-glucose) on the cellular productivity of nitric oxide (NO) in bovine aortic endothelial cells (BAEC). We had previously reported (Kimura C, Oike M, and Ito Y. Circ Res, 82: 677–685, 1998) that glucose overload impairs Ca2+mobilization due to an accumulation of superoxide anions (O2−) in BAEC. In control cells, ATP induced an increase in NO production, assessed by diaminofluorescein 2 (DAF-2), an NO-sensitive fluorescent dye, mainly due to Ca2+entry. In contrast, ATP-induced increase in DAF-2 fluorescence was impaired by glucose overload, which was restored by superoxide dismutase, but not by catalase or deferoxamine. Furthermore, pyrogallol, an O2−donor, also attenuated ATP-induced increase in DAF-2 fluorescence. In contrast, a nonspecific intracellular Ca2+concentration increase induced by the Ca2+ionophore A-23187, which depletes the intracellular store sites, elevated DAF-2 fluorescence in both control and highd-glucose-treated cells in Ca2+-free solution. These results indicate that glucose overload impairs NO production by the O2−-mediated attenuation of Ca2+entry.
The iterative two-stage population approach to IVGTT minimal modeling: improved precision with reduced sampling
Authors: Vicini Paolo , Cobelli Claudio
Published: December 2017

The minimal model method is widely used to estimate glucose effectiveness (SG) and insulin sensitivity (SI) from intravenous glucose tolerance test (IVGTT) data. In the standard protocol (sIVGTT, 0.33 g/kg glucose bolus given at time 0), which allows the simultaneous assessment of β-cell function, the precision of the individualized estimates often degrades and particularly so in the presence of reduced sampling schedules. Here, we investigated the use of a population approach, the iterative two-stage (ITS) approach, to analyze 16 sIVGTTs in healthy subjects and to obtain refined estimates of SG and SI in the population and in the individual subjects. The ITS is based on calculation of the population mean and standard deviation of the parameters at each iteration and then use of them as prior information for the individual analyses. Theoretically, the use of a prior in the ITS should improve the precision of the individual estimates. The customary approach (standard two stage, STS), where modeling is performed separately for each individual subject, does not take the population knowledge into account. We used both frequent (FSS, 30 samples) and (quasi-optimally) reduced (RSS, 14 samples) sampling schedules. For the FSS, STS gave estimates (mean ± SD) for SG = 2.66 ± 1.09 × 10−2 · min−1 and SI = 6.46 ± 6.99 10−4 · min−1 · μU−1 · ml, with an average precision of 51 (range 5–176) and 33% (3–91), respectively. RSS radically worsened the precision of both SG and SI. However, RSS and ITS gave SG = 2.59 ± 0.73 and SI = 6.06 ± 7.28, with an average precision of 23 (12–42) and 27% (), respectively. In conclusion, population minimal modeling of sIVGTT data improves the precision of individual estimates of glucose effectiveness and insulin sensitivity, as the theory predicts, and, even with reduced sampling, the improvement is substantial.
Determination of muscle-specific glucose flux using radioactive stereoisomers and microdialysis
Authors: MacLean David A. , Ettinger Steven M. , Sinoway Lawrence I. , Lanoue Kathryn F.
Published: December 2017

The purpose of the present study was to evaluate a novel approach for determining skeletal muscle-specific glucose flux using radioactive stereoisomers and the microdialysis technique. Microdialysis probes were inserted into the vastus lateralis muscle of human subjects and perfused (4 μl/min) with a Ringer solution containing small amounts of radioactived- and l-glucose as the internal reference markers for determining probe recovery as well as varying concentrations of insulin (0–10 μM). The rationale behind this approach was that both stereoisomers would be equally affected by the factors that determine probe recovery, with the exception ofl-glucose, which is nonmetabolizable and would not be influenced by tissue uptake. Therefore, any differences in the probe recovery ratios between the d- andl-stereoisomers represent changes in skeletal muscle glucose uptake directly at the tissue level. There were no differences in probe recovery between the d- (42.3 ± 3.5%) andl- (41.2 ± 3.5) stereoisomers during the control period (no insulin), which resulted in a D/L ratio of 1.04 ± 0.03. However, during insulin perfusion (1 μM), The D/L ratio increased to 1.62 ± 0.08 and 1.58 ± 0.07 ( P< 0.05) during the two collection (0–15 and 15–30 min) periods, respectively. This was accomplished solely by an increase ( P < 0.05) in d-glucose probe recovery, asl-glucose probe recovery remained unchanged. In a second set of experiments, the perfusion of 10 μM insulin did not increase the D/L ratio (1.40 ± 0.11) above that observed during 1.0 μM (1.41 ± 0.07) insulin perfusion. These data suggest that this method is sufficiently sensitive to detect differences in insulin-stimulated glucose uptake; thus the use of radioactive stereoisomers in conjunction with the microdialysis technique provides a novel and useful technique for determining tissue-specific glucose flux and insulin sensitivity.
An in vivo study of ovine placental transport of essential amino acids
Authors: Paolini Cinzia L. , Meschia Giacomo , Fennessey Paul V. , Pike Adrian W. , Teng Cecilia , Battaglia Frederick C. , Wilkening Randall B.
Published: December 2017

Under normal physiological conditions, essential amino acids (EA) are transported from mother to fetus at different rates. The mechanisms underlying these differences include the expression of several amino acid transport systems in the placenta and the regulation of EA concentrations in maternal and fetal plasma. To study the relation of EA transplacental flux to maternal plasma concentration, isotopes of EA were injected into the circulation of pregnant ewes. Measurements of concentration and molar enrichment in maternal and fetal plasma and of umbilical plasma flow were used to calculate the ratio of transplacental pulse flux to maternal concentration (clearance) for each EA. Five EA (Met, Phe, Leu, Ile, and Val) had relatively high and similar clearances and were followed, in order of decreasing clearance, by Trp, Thr, His, and Lys. The five high-clearance EA showed strong correlation ( r2= 0.98) between the pulse flux and maternal concentration. The study suggests that five of the nine EA have similar affinity for a rate-limiting placental transport system that mediates rapid flux from mother to fetus, and that differences in transport rates within this group of EA are determined primarily by differences in maternal plasma concentration.
Regulatory role of arginase I and II in nitric oxide, polyamine, and proline syntheses in endothelial cells
Authors: Li Hui , Meininger Cynthia J. , Hawker James R. , Haynes Tony E. , Kepka-Lenhart Diane , Mistry Sanjay K. , Morris Sidney M. , Wu Guoyao
Published: December 2017

Endothelial cells (EC) metabolize l-arginine mainly by arginase, which exists as two distinct isoforms, arginase I and II. To understand the roles of arginase isoforms in EC arginine metabolism, bovine coronary venular EC were stably transfected with the Escherichia coli lacZ gene (lacZ-EC, control), rat arginase I cDNA (AI-EC), or mouse arginase II cDNA (AII-EC). Western blots and enzymatic assays confirmed high-level expression of arginase I in the cytosol of AI-EC and of arginase II in mitochondria of AII-EC. For determining arginine catabolism, EC were cultured for 24 h in DMEM containing 0.4 mM l-arginine plus [1-14C]arginine. Urea formation, which accounted for nearly all arginine consumption by these cells, was enhanced by 616 and 157% in AI-EC and AII-EC, respectively, compared with lacZ-EC. Arginine uptake was 31–33% greater in AI-EC and AII-EC than in lacZ-EC. Intracellular arginine content was 25 and 11% lower in AI-EC and AII-EC, respectively, compared with lacZ-EC. Basal nitric oxide (NO) production was reduced by 60% in AI-EC and by 47% in AII-EC. Glutamate and proline production from arginine increased by 164 and 928% in AI-EC and by 79 and 295% in AII-EC, respectively, compared with lacZ-EC. Intracellular content of putrescine and spermidine was increased by 275 and 53% in AI-EC and by 158 and 43% in AII-EC, respectively, compared with lacZ-EC. Our results indicate that arginase expression can modulate NO synthesis in bovine venular EC and that basal levels of arginase I and II are limiting for endothelial syntheses of polyamines, proline, and glutamate and may have important implications for wound healing, angiogenesis, and cardiovascular function.
Age effect on transcript levels and synthesis rate of muscle MHC and response to resistance exercise
Authors: Balagopal Prabhakaran , Schimke Jill Coenen , Ades Philip , Adey Deborah , Nair K. Sreekumaran
Published: December 2017

Experimental evidence indicates that a lower synthesis rate of muscle contractile protein myosin heavy chain (MHC) occurs in age-related muscle wasting and weakness. To determine the molecular mechanism of this lower synthesis of MHC, we measured transcript levels of isoforms of MHC (MHCI, MHCIIa, and MHCIIx) in muscle biopsy samples of 7 young (20–27 yr), 12 middle-aged (47–60 yr), and 14 older (>65 yr) people. We further determined the effect of 3 mo of resistance exercise training (exercise) vs. nonintervention (control) on transcript levels of MHC isoforms on these subjects and the fractional synthesis rate (FSR) of MHC in 39 people aged 46–79 yr. MHCI mRNA levels did not significantly change with age, but MHCIIa decreased 38% ( P < 0.05) from young to middle age and further decreased 50% ( P < 0.05) from middle to old age. MHCIIx decreased 84% ( P < 0.05) from young to middle age and 48% from middle to old age ( P < 0.05). Exercise increased FSR of MHC by 47% ( P < 0.01) and mixed muscle protein by 56% ( P < 0.05). Exercise training results in an increase (85%) in transcript levels of MHCI and a decrease in the transcript levels of MHCIIa and MHCIIx. In conclusion, an age-related lowering of the transcript levels of MHCIIa and MHCIIx is not reversed by exercise, whereas exercise results in a higher synthesis rate of MHC in association with an increase in MHCI isoform transcript levels.
Pulsatile growth hormone secretion decreasesS-adenosylmethionine synthetase in rat liver
Authors: Oscarsson Jan , Gardmo Cissi , Edén Staffan , Mode Agneta
Published: December 2017

S-adenosylmethionine synthetase (AdoMet synthetase) is responsible for the synthesis of the major methyl donor S-adenosylmethionine. The AdoMet synthetase gene was identified by subtractive suppressive hybridization as being expressed at higher levels in the liver of rats continuously exposed to growth hormone (GH) than in rats intermittently exposed to the hormone. Further studies on the regulation of AdoMet synthetase showed that the activity and mRNA levels were higher in female than in male rats. Hypophysectomy increased AdoMet synthetase mRNA in both male and female rats. Combined thyroxine and cortisol treatment of hypophysectomized rats had no effect on AdoMet synthetase mRNA levels. Two daily injections of GH for 7 days, mimicking the male secretory pattern of GH, decreased AdoMet synthetase activity and mRNA levels. A continuous infusion of GH, mimicking the female secretory pattern of GH, had small or no effects on AdoMet synthetase activity and decreased the mRNA levels to a lesser degree than two daily injections. It is concluded that the lower AdoMet synthetase activity in male rats is due to an inhibitory effect of the male characteristic pulsatile secretory pattern of GH on AdoMet synthetase mRNA expression.
Acid-labile subunit regulation during the early stages of liver regeneration: implications for glucoregulation
Authors: Delhanty Patric J. D. , Scott Carolyn D. , Babu Sunita , Baxter Robert C.
Published: December 2017

The initiation of liver regeneration is regulated by endogenously produced growth factors and cytokines and is accompanied by suppression of growth hormone (GH) binding to hepatocytes. We have demonstrated some of these factors, particularly GH, which modulate acid-labile subunit (ALS) expression in vitro. Consequently, we investigated ALS hepatic mRNA and serum levels in rats for 24 h after partial hepatectomy (PHx). There was a significant suppression of ALS gene expression (∼50%, P < 0.005) and serum levels (∼30%, P < 0.02) by 12 h in PHx rats relative to controls. Relative to intact animals, hepatic mRNA and serum levels of ALS were suppressed by ∼60% at 24 h. Similarly, hepatic GH receptor mRNA levels were significantly reduced in PHx animals. Moreover, hepatocytes isolated from PHx animals were less responsive to GH than those from controls. Overall, our results demonstrate that suppression of ALS gene expression and serum levels during liver regeneration relates to lowered hepatic GH sensitivity. Suppressed circulating ALS may alter insulin-like growth factor bioavailability and constitute a mechanism to maintain relatively normal glucoregulation after loss of liver mass.
Desensitization of angiotensin II: effect on [Ca2+]i, inositol triphosphate, and prolactin in pituitary cells
Authors: González Iglesias Arturo , Suárez Cecilia , Feierstein Claudia , Dı́az-Torga Graciela , Becu-Villalobos Damasia
Published: December 2017

Activation of pituitary angiotensin (ANG II) type 1 receptors (AT1) mobilizes intracellular Ca2+, resulting in increased prolactin secretion. We first assessed desensitization of AT1receptors by testing ANG II-induced intracellular Ca2+concentration ([Ca2+]i) response in rat anterior pituitary cells. A period as short as 1 min with 10−7M ANG II was effective in producing desensitization (remaining response was 66.8 ± 2.1% of nondesensitized cells). Desensitization was a concentration-related event (EC50: 1.1 nM). Although partial recovery was obtained 15 min after removal of ANG II, full response could not be achieved even after 4 h (77.6 ± 2.4%). Experiments with 5 × 10−7M ionomycin indicated that intracellular Ca2+stores of desensitized cells had already recovered when desensitization was still significant. The thyrotropin-releasing hormone (TRH)-induced intracellular Ca2+peak was attenuated in the ANG II-pretreated group. ANG II pretreatment also desensitized ANG II- and TRH-induced inositol phosphate generation (72.8 ± 3.5 and 69.6 ± 6.1%, respectively, for inositol triphosphate) and prolactin secretion (53.4 ± 2.3 and 65.1 ± 7.2%), effects independent of PKC activation. We conclude that, in pituitary cells, inositol triphosphate formation, [Ca2+]imobilization, and prolactin release in response to ANG II undergo rapid, long-lasting, homologous and heterologous desensitization.
Adverse metabolic consequences of HIV protease inhibitor therapy: the search for a central mechanism
Authors: Hruz Paul W. , Murata Haruhiko , Mueckler Mike
Published: December 2017

Although the clinical introduction of human immunodeficiency virus (HIV) protease inhibitors (PIs) has resulted in a dramatic decline in HIV-related morbidity and mortality, it is now recognized that PI therapy is associated with serious adverse metabolic effects, including peripheral lipoatrophy, increased visceral fat, hyperlipidemia, and insulin resistance. Despite increasing awareness of this metabolic syndrome, the etiology of these side effects remains obscure. This review critically examines current mechanistic hypotheses in the context of the available experimental data. To date, a single unifying explanation for this syndrome has not been confirmed. As data accumulate, it is becoming clear that PIs lack precision in their cellular targets and it is likely that many of the side effects of these drugs are due to inhibition of a number of unrelated molecules.
Fructose augments infection-impaired net hepatic glucose uptake during TPN administration
Authors: Donmoyer Christine M. , Ejiofor Joseph , Lacy D. Brooks , Chen Sheng-Song , McGuinness Owen P.
Published: December 2017

During chronic total parenteral nutrition (TPN), net hepatic glucose uptake (NHGU) and net hepatic lactate release (NHLR) are markedly reduced (↓∼45 and ∼65%, respectively) with infection. Because small quantities of fructose are known to augment hepatic glucose uptake and lactate release in normal fasted animals, the aim of this work was to determine whether acute fructose infusion with TPN could correct the impairments in NHGU and NHLR during infection. Chronically catheterized conscious dogs received TPN for 5 days via the inferior vena cava at a rate designed to match daily basal energy requirements. On the third day of TPN administration, a sterile (SHAM, n = 12) or Escherichia coli-containing (INF, n = 11) fibrin clot was implanted in the peritoneal cavity. Forty-two hours later, somatostatin was infused with intraportal replacement of insulin (12 ± 2 vs. 24 ± 2 μU/ml, SHAM vs. INF, respectively) and glucagon (24 ± 4 vs. 92 ± 5 pg/ml) to match concentrations previously observed in sham and infected animals. After a 120-min basal period, animals received either saline (Sham+S, n = 6; Inf+S, n = 6) or intraportal fructose (0.7 mg · kg−1· min−1; Sham+F, n = 6; Inf+F, n = 5) infusion for 180 min. Isoglycemia of 120 mg/dl was maintained with a variable glucose infusion. Combined tracer and arteriovenous difference techniques were used to assess hepatic glucose metabolism. Acute fructose infusion with TPN augmented NHGU by 2.9 ± 0.4 and 2.5 ± 0.3 mg · kg−1· min−1in Sham+F and Inf+F, respectively. The majority of liver glucose uptake was stored as glycogen, and NHLR did not increase substantially. Therefore, despite an infection-induced impairment in NHGU and different hormonal environments, small amounts of fructose enhanced NHGU similarly in sham and infected animals. Glycogen storage, not lactate release, was the preferential fate of the fructose-induced increase in hepatic glucose disposal in animals adapted to TPN.