bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyruvate overrides inhibition of PDH during exercise after a low-carbohydrate diet
Authors: St. Amand Timothy A. , Spriet Lawrence L. , Jones Norman L. , Heigenhauser George J. F.
Published: December 2017

The effects of carbohydrate deprivation on the regulation of pyruvate dehydrogenase (PDH) were studied at rest and during moderate-intensity exercise. An inhibitory effect of a chronic low-carbohydrate diet (LCD) on the active form of PDH (PDHa) mediated by a stable increase in PDH kinase (PDHK) activity has recently been reported (Peters SJ, Howlett RA, St. Amand TA, Heigenhauser GJF, and Spriet LL. Am J Physiol Endocrinol Metab 275: E980-E986, 1998.). In the present study, seven males cycled at 65% maximal O2uptake for 30 min after a 6-day LCD. Exercise was repeated 1 wk later after a mixed diet (MD). Muscle biopsies were sampled from the vastus lateralis at rest and at 2 and 30 min of exercise. At rest, PDHa activity (0.18 ± 0.04 vs. 0.63 ± 0.18 mmol · min−1· kg wet wt−1), muscle glycogen content (310.2 ± 36.9 vs. 563.9 ± 32.6 mmol/kg dry wt), and muscle lactate content (2.6 ± 0.3 vs. 4.2 ± 0.6 mmol/kg dry wt) were significantly lower after the LCD. Resting muscle acetyl-CoA (10.8 ± 1.9 vs. 7.4 ± 0.8 μmol/kg dry wt) and acetylcarnitine (5.3 ± 1.4 vs. 1.6 ± 0.3 mmol/kg dry wt) contents were significantly elevated after the LCD. During exercise, PDHa, glycogenolytic rate (LCD 5.8 ± 0.4 vs. MD 6.9 ± 0.2 mmol · min−1· kg dry wt−1), and muscle concentrations of acetylcarnitine, pyruvate, and lactate increased to the same extent in both conditions. The results of the present study suggest that inhibition of resting PDH by elevated PDHK activity after a LCD may be overridden by the availability of muscle pyruvate during exercise.
Vanadate restores glucose 6-phosphate in diabetic rats: a mechanism to enhance glucose metabolism
Authors: Sun Qian , Sekar Natesampillai , Goldwaser Itzhak , Gershonov Eytan , Fridkin Mati , Shechter Yoram
Published: December 2017

Vanadate mimics the metabolic actions of insulin. In diabetic rodents, vanadate also sensitizes peripheral tissues to insulin. We have analyzed whether this latter effect is brought about by a mechanism other than the known insulinomimetic actions of vanadium in vitro. We report that the levels of glucose 6-phosphate (G-6- P) in adipose, liver, and muscle of streptozotocin-treated (STZ)-hyperglycemic rats are 77, 50, and 58% of those in healthy control rats, respectively. Normoglycemia was induced by vanadium or insulin therapy or by phlorizin. Vanadate fully restored G-6- P in all three insulin-responsive peripheral tissues. Insulin did not restore G-6- P in muscle, and phlorizin was ineffective in adipose and muscle. Incubation of diabetic adipose explants with glucose and vanadate in vitro increased lipogenic capacity three- to fourfold (half-maximally effective dose = 11 ± 1 μM vanadate). Lipogenic capacity was elevated when a threshold level of ∼7.5 ± 0.3 nmol G-6- P/g tissue was reached. In summary, 1) chronic hyperglycemia largely reduces intracellular G-6- P in all three insulin-responsive tissues; 2) vanadate therapy restores this deficiency, but insulin therapy does not restore G-6- P in muscle tissue; 3) induction of normoglycemia per se (i.e., by phlorizin) restores G-6- P in liver only; and 4) glucose and vanadate together elevate G-6- P in adipose explants in vitro and significantly restore lipogenic capacity above the threshold of G-6- P level. We propose that hyperglycemia-associated decrease in peripheral G-6- P is a major factor responsible for peripheral resistance to insulin. The mechanism by which vanadate increases peripheral tissue capacity to metabolize glucose and to respond to the hormone involves elevation of this hexose phosphate metabolite and the cellular consequences of this elevated level of G-6- P.
The direct effects of catecholamines on hepatic glucose production occur via α1- and β2-receptors in the dog
Authors: Chu Chang An , Sindelar Dana K. , Igawa Kayano , Sherck Stephanie , Neal Doss W. , Emshwiller Maya , Cherrington Alan D.
Published: December 2017

The role of α- and β-adrenergic receptor subtypes in mediating the actions of catecholamines on hepatic glucose production (HGP) was determined in sixteen 18-h-fasted conscious dogs maintained on a pancreatic clamp with basal insulin and glucagon. The experiment consisted of a 100-min equilibration, a 40-min basal, and two 90-min test periods in groups 1 and 2, plus a 60-min third test period in groups 3 and 4. In group 1 [α-blockade with norepinephrine (α-blo+NE)], phentolamine (2 μg · kg−1 · min−1) was infused portally during both test periods, and NE (50 ng · kg−1 · min−1) was infused portally at the start of test period 2. In group 2, β-blockade with epinephrine (β-blo+EPI), propranolol (1 μg · kg−1 · min−1) was infused portally during both test periods, and EPI (8 ng · kg−1 · min−1) was infused portally during test period 2. In group 3 (α1-blo+NE), prazosin (4 μg · kg−1 · min−1) was infused portally during all test periods, and NE (50 and 100 ng · kg−1 · min−1) was infused portally during test periods 2 and 3, respectively. In group 4(β2-blo+EPI), butoxamine (40 μg · kg−1 · min−1) was infused portally during all test periods, and EPI (8 and 40 ng · kg−1 · min−1) was infused portally during test periods 2 and 3, respectively. In the presence of α- or α1-adrenergic blockade, a selective rise in hepatic sinusoidal NE failed to increase net hepatic glucose output (NHGO). In a previous study, the same rate of portal NE infusion had increased NHGO by 1.6 ± 0.3 mg · kg−1 · min−1. In the presence of β- or β2-adrenergic blockade, the selective rise in hepatic sinusoidal EPI caused by EPI infusion at 8 ng · kg−1 · min−1 also failed to increase NHGO. In a previous study, the same rate of EPI infusion had increased NHGO by 1.6 ± 0.4 mg · kg−1 · min−1. In conclusion, in the conscious dog, the direct effects of NE and EPI on HGP are predominantly mediated through α1- and β2-adrenergic receptors, respectively.
Effects of oral administration of a synthetic fragment of human growth hormone on lipid metabolism
Authors: Heffernan M. A. , Jiang W. J. , Thorburn A. W. , Ng F. M.
Published: December 2017

A small synthetic peptide sequence of human growth hormone (hGH), AOD-9401, has lipolytic and antilipogenic activity similar to that of the intact hormone. Here we report its effect on lipid metabolism in rodent models of obesity and in human adipose tissue to assess its potential as a pharmacological agent for the treatment of human obesity. C57BL/6J ( ob/ob) mice were orally treated with either saline ( n = 8) or AOD-9401 ( n = 10) for 30 days. From day 16onward, body weight gain in AOD-9401-treated animals was significantly lower than that of saline-treated controls. Food consumption did not differ between the two groups. Analyses of adipose tissue ex vivo revealed that AOD-9401 significantly reduced lipogenic activity and increased lipolytic activity in this tissue. Increased catabolism was also reflected in an acute increase in energy expenditure and glucose and fat oxidation in ob/ob mice treated with AOD-9401. In addition, AOD-9401 increased in vitro lipolytic activity and decreased lipogenic activity in isolated adipose tissue from obese rodents and humans. Together, these findings indicate that oral administration of AOD-9401 alters lipid metabolism in adipose tissue, resulting in a reduction of weight gain in obese animals. The marked lipolytic and antilipogenic actions of AOD-9401 in human adipose tissues suggest that this small synthetic hGH peptide has potential in the treatment of human obesity.
Effect of exercise training on in vivo lipolysis in intra-abdominal adipose tissue in rats
Authors: Enevoldsen L. H. , Stallknecht B. , Fluckey J. D. , Galbo H.
Published: December 2017

Intra-abdominal obesity is associated with cardiovascular disease and non-insulin-dependent diabetes mellitus, and physical training has been suggested to alleviate these conditions. We compared epinephrine-stimulated lipolysis in vivo in three intra-abdominal adipose tissues (ATs: retroperitoneal, parametrial, and mesenteric) and in subcutaneous AT, and we also studied the effect of physical training. Moreover, we studied the effect of physical training on epinephrine-stimulated lipolysis in muscle in vivo. Female rats were either swim trained (15 wk, n = 8) or sedentary ( n = 7). Under anesthesia, a two-stage intravenous epinephrine infusion (60 min of 80 and 200 ng · kg−1· min−1, respectively) was carried out, and local interstitial glycerol concentration was measured by the microdialysis technique. Blood flow was measured by microspheres. Training increased blood flow in all ATs [on average: 73 ± 12 (trained) vs. 14 ± 4 (sedentary) ml · 100 g−1· min−1, P < 0.05]; nevertheless, epinephrine-stimulated interstitial glycerol concentrations were increased or unchanged. Interstitial glycerol concentration was higher in intra-abdominal than in subcutaneous AT in both trained and sedentary rats. In skeletal muscle, interstitial glycerol concentration and blood flow did not differ between trained and sedentary rats. In conclusion, in vivo lipolysis is higher both in the basal state and during epinephrine-stimulation in intra-abdominal than in subcutaneous AT, and training may be beneficial in alleviating intra-abdominal obesity by enhancing lipolysis in intra-abdominal fat depots.
A specific binding moiety for 1,25-dihydroxyvitamin D3in basal lateral membranes of carp enterocytes
Authors: Nemere Ilka , Larsson Dennis , Sundell Kristina
Published: December 2017

Carp (Cyprinus carpio), a freshwater fish that lives in a low-calcium environment, and Atlantic cod (Gadus morhua), a seawater fish that lives in a high-calcium environment, were studied for the presence of a novel membrane binding protein (“receptor”) for the vitamin D metabolite, 1,25-dihydroxyvitamin D3[1,25(OH)2D3]. Basal lateral membranes from enterocytes of either species were prepared and analyzed for specific saturable binding. Membranes from carp revealed a dissociation constant of 1.23 nM with a maximal binding capacity of 212 fmol/mg protein. In comparison, membranes from Atlantic cod enterocytes revealed very low and nonsignificant levels of specific binding. The [3H]1,25(OH)2D3binding activity in carp was further characterized for protein dependence, detergent extractability, and competition for binding with the metabolites 25(OH)D3and 24 R,25(OH)2D3. Finally, introduction of 1,25(OH)2D3to isolated carp enterocytes enhanced protein kinase C activity within 5 min, whereas intracellular Ca2+concentrations were unaffected by a range of 1,25(OH)2D3concentrations, as judged by fura 2 fluorescence. Thus the binding moiety may be a putative plasma membrane receptor for vitamin D, because it is functionally coupled to at least one signal transduction pathway.
Impaired dilation of coronary arterioles during increases in myocardial O2 consumption with hyperglycemia
Authors: Ammar Richard F. , Gutterman David D. , Brooks Leonard A. , Dellsperger Kevin C.
Published: December 2017

Previous studies showed that nitric oxide (NO) plays an important role in coronary arteriolar dilation to increases in myocardial oxygen consumption (MV˙o 2). We sought to evaluate coronary microvascular responses to endothelium-dependent and to endothelium-independent vasodilators in an in vivo model. Microvascular diameters were measured using intravital microscopy in 10 normal (N) and 9 hyperglycemic (HG; 1 wk alloxan, 60 mg/kg iv) dogs during suffusion of acetylcholine (1, 10, and 100 μM) or nitroprusside (1, 10, and 100 μM) to test the effects on endothelium-dependent and -independent dilation. During administration of acetylcholine, coronary arteriolar dilation was impaired in HG, but was normal during administration of nitroprusside. To examine a physiologically important vasomotor response, 10 N and 7 HG control, 5 HG and 5 N during superoxide dismutase (SOD), and 5 HG and 4 N after SQ29,548 (SQ; thromboxane A2/prostaglandin H2receptor antagonist) dogs were studied at three levels of MV˙o 2: at rest, during dobutamine (DOB; 10 μg · kg−1 · min−1 iv), and during DOB with rapid atrial pacing (RAP; 280 ± 10 beats/min). During dobutamine, coronary arterioles dilated similarly in all groups, and the increase in MV˙o 2 was similar among the groups. However, during the greater metabolic stimulus (DOB+RAP), coronary arterioles in N dilated (36 ± 4% change from diameter at rest) significantly more than HG (16 ± 3%, P< 0.05). In HG+SQ and in HG+SOD, coronary arterioles dilated similarly to N, and greater than HG ( P < 0.05). MV˙o 2 during DOB+RAP was similar among groups. Normal dogs treated with SOD and SQ29,548 were not different from untreated N dogs. Thus, in HG dogs, dilation of coronary arterioles is selectively impaired in response to administration of the endothelium-dependent vasodilator acetylcholine and during increases in MV˙o 2.
Lipid oxidation is reduced in obese human skeletal muscle
Authors: Kim Jong-Yeon , Hickner Robert C. , Cortright Ronald L. , Dohm G. Lynis , Houmard Joseph A.
Published: December 2017

The purpose of this study was to discern cellular mechanisms that contribute to the suppression of lipid oxidation in the skeletal muscle of obese individuals. Muscle was obtained from obese [body mass index (BMI), 38.3 ± 3.1 kg/m2] and lean (BMI, 23.8 ± 0.9 kg/m2) women, and fatty acid oxidation was studied by measuring 14CO2 production from14C-labeled fatty acids. Palmitate oxidation, which is at least partially dependent on carnitine palmitoyltransferase-1 (CPT-1) activity, was depressed ( P < 0.05) by ≈50% with obesity (6.8 ± 2.2 vs. 13.7 ± 1.4 nmole CO2 · g−1 · h−1). The CPT-1-independent event of palmitoyl carnitine oxidation was also depressed ( P < 0.01) by ≈45%. There were significant negative relationships ( P < 0.05) for adiposity with palmitate ( r = −0.76) and palmitoyl carnitine ( r = −0.82) oxidation. Muscle CPT-1 and citrate synthase activity, an index of mitochondrial content, were also significantly ( P < 0.05) reduced (≈35%) with obesity. CPT-1 ( r = −0.48) and citrate synthase ( r = −0.65) activities were significantly ( P < 0.05) related to adiposity. These data suggest that lesions at CPT-1 and post-CPT-1 events, such as mitochondrial content, contribute to the reduced reliance on fat oxidation evident in human skeletal muscle with obesity.
Lumped constant for [18F]fluorodeoxyglucose in skeletal muscles of obese and nonobese humans
Authors: Peltoniemi Pauliina , Lönnroth Peter , Laine Hanna , Oikonen Vesa , Tolvanen Tuula , Grönroos Tove , Strindberg Lena , Knuuti Juhani , Nuutila Pirjo
Published: December 2017

Quantitative 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) positron emission tomography (PET) has been widely used to calculate glucose utilization in skeletal muscle. FDG-PET results depend partly on the lumped constant (LC), which accounts for the differences in the transport and phosphorylation between [18F]FDG and glucose. In this study, we estimated the LC for [18F]FDG directly in normal and in insulin-resistant obese subjects by combining FDG PET with the microdialysis technique. Eight obese [age 29.4 ± 1.0 yr, body mass index (BMI) 33.6 ± 1.0 kg/m2] and eight nonobese (age 25.0 ± 1.0 yr, BMI 23.1 ± 1.0 kg/m2) males were studied during euglycemic hyperinsulinemia (1 mU · kg−1· min−1for 150 min). Muscle blood flow was measured using15O-labeled water and PET. Muscle [18F]FDG uptake (rGUFDG) was calculated with Patlak graphic analysis. Interstitial glucose concentration of the quadriceps femoris muscle was measured simultaneously with [18F]FDG scanning using microdialysis. Muscle glucose uptake (by microdialysis, rGUMD) was calculated by multiplying glucose extraction by regional muscle blood flow. A significant correlation was found between rGUMDand rGUFDG( r = 0.78, P < 0.01). The LC was determined as the ratio of the rGUFDGto the rGUMD. The LC averaged 1.16 ± 0.16 and was similar in the obese and nonobese subjects (1.15 ± 0.11 vs. 1.16 ± 0.07, respectively, not significant). In conclusion, the microdialysis technique can be reliably combined with FDG PET to measure glucose uptake in skeletal muscle. Direct measurements with these two independent techniques suggest an LC value of 1.2 for [18F]FDG in human skeletal muscle during insulin stimulation, and the LC appears not to be sensitive to insulin resistance.
Effect of sepsis on eIE4E availability in skeletal muscle
Authors: Vary Thomas C. , Kimball Scot R.
Published: December 2017

Chronic septic abscess formation causes an inhibition of protein synthesis in gastrocnemius that is not observed in rats with a sterile abscess. The inhibition is associated with an impaired translation initiation. The present study was designed to investigate the effects of sepsis on phosphorylation and availability of eukaryotic initiation factor (eIF)4E in gastrocnemius 5 days after induction of a sterile or septic abscess. Neither sepsis nor sterile inflammation altered the extent of eIF4E phosphorylation. Moreover, no changes in the amount of the binding protein 4E-BP1 associated with eIF4E or in the phosphorylation of 4E-BP1 were observed during sepsis or sterile inflammation. In contrast, sepsis and sterile inflammation caused a reduction in the relative amount of eIF4G bound to eIF4E compared with controls. The diminished amount of eIF4G bound to eIF4E was not the result of a reduced abundance of eIF4E. Sepsis, but not sterile inflammation, caused an increase in the cellular abundance of eIF4E. The results provide evidence that alterations in the eIF4E system are probably not rate controlling for the synthesis of total, mixed proteins in gastrocnemius during sepsis. Instead, on the basis of our previous studies, changes in eIF2B appear to be responsible for limiting protein synthesis in skeletal muscle during sepsis.
Whole body protein kinetics in women: effect of pregnancy and IDDM during anabolic stimulation
Authors: Whittaker Paul G. , Lee Choy H. , Taylor Roy
Published: December 2017

The effects of pregnancy and type 1 diabetes [insulin-dependent diabetes mellitus (IDDM)] on protein metabolism are still uncertain. Therefore, six normal and five IDDM women were studied during and after pregnancy, using [13C]leucine and [2H5]phenylalanine with a hyperinsulinemic-euglycemic clamp and amino acid infusion. Fasting total plasma amino acids were lower in pregnancy in normal but not IDDM women (2,631 ± 427 vs. 2,057 ± 471 and 2,523 ± 430 vs. 2,500 ± 440 μmol/l, respectively). Whole body protein breakdown (leucine) increased in pregnancy [change in normal (ΔN) and IDDM women (ΔD) 0.59 ± 0.40 and 0.48 ± 0.26 g · kg−1 · day−1, both P < 0.001], whereas reductions in protein breakdown due to insulin/amino acids (ΔN −0.57 ± 0.19, ΔD −0.58 ± 0.20 g · kg−1 · day−1, both P < 0.001) were unaffected by pregnancy. Protein breakdown in IDDM women was not higher than normal, and neither pregnancy nor type 1 diabetes altered the insulin sensitivity of amino acid turnover. Nonoxidized leucine disposal (protein synthesis) increased in pregnancy (ΔN 0.67 ± 0.45, ΔD 0.64 ± 0.34 g · kg−1 · day−1, both P < 0.001). Pregnancy reduced the response of phenylalanine hydroxylation to insulin/amino acids in both groups (ΔN −1.14 ± 0.74, ΔD −1.12 ± 0.77 g · kg−1 · day−1, both P < 0.05). These alterations may enable amino acid conservation for protein synthesis and accretion in late pregnancy. Well-controlled type 1 diabetes caused no abnormalities in the regulation of basal or stimulated protein metabolism.
Myostatin inhibits cell proliferation and protein synthesis in C2C12 muscle cells
Authors: Taylor Wayne E. , Bhasin Shalender , Artaza Jorge , Byhower Frances , Azam Mohd , Willard Darril H. , Kull Frederick C. , Gonzalez-Cadavid Nestor
Published: December 2017

Myostatin mutations in mice and cattle are associated with increased muscularity, suggesting that myostatin is a negative regulator of skeletal muscle mass. To test the hypothesis that myostatin inhibits muscle cell growth, we examined the effects of recombinant myostatin in mouse skeletal muscle C2C12 cells. After verification of the expression of cDNA constructs in a cell-free system and in transfected Chinese hamster ovary cells, the human recombinant protein was expressed as the full-length (375-amino acid) myostatin in Drosophila cells (Mst375D), or the 110-amino acid carboxy-terminal protein in Escherichia coli(Mst110EC). These proteins were identified by immunoblotting and were purified. Both Mst375D and Mst110EC dose dependently inhibited cell proliferation (cell count and Formazan assay), DNA synthesis ([3H]thymidine incorporation), and protein synthesis ([1-14C]leucine incorporation) in C2C12 cells. The inhibitory effects of both proteins were greater in myotubes than in myoblasts. Neither protein had any significant effects on protein degradation or apoptosis. In conclusion, recombinant myostatin proteins inhibit cell proliferation, DNA synthesis, and protein synthesis in C2C12muscle cells, suggesting that myostatin may control muscle mass by inhibiting muscle growth or regeneration.
Parasympathetic inhibition of sympathetic neural activity to the pancreas
Authors: Benthem Lambertus , Mundinger Thomas O. , Taborsky Gerald J.
Published: December 2017

The present study tested the hypothesis that activation of the parasympathetic nervous system could attenuate sympathetic activation to the pancreas. To test this hypothesis, we measured pancreatic norepinephrine (NE) spillover (PNESO) in anesthetized dogs during bilateral thoracic sympathetic nerve stimulation (SNS; 8 Hz, 1 ms, 10 mA, 10 min) with and without (randomized design) simultaneous bilateral cervical vagal nerve stimulation (VNS; 8 Hz, 1 ms, 10 mA, 10 min). During SNS alone, PNESO increased from the baseline of 431 ± 88 pg/min to an average of 5,137 ± 1,075 pg/min ( P < 0.05) over the stimulation period. Simultaneous SNS and VNS resulted in a significantly ( P < 0.01) decreased PNESO response [from 411 ± 61 to an average of 2,760 ± 1,005 pg/min ( P < 0.05) over the stimulation period], compared with SNS alone. Arterial NE levels increased during SNS alone from 130 ± 11 to ∼600 pg/ml ( P < 0.05); simultaneous SNS and VNS produced a significantly ( P < 0.05) smaller response (142 ± 17 to 330 pg/ml). Muscarinic blockade could not prevent the effect of VNS from reducing the increase in PNESO or arterial NE in response to SNS. It is concluded that parasympathetic neural activity opposes sympathetic neural activity not only at the level of the islet but also at the level of the nerves. This neural inhibition is not mediated via muscarinic mechanisms.
Effects of cellular ATP depletion on glucose transport and insulin signaling in 3T3-L1 adipocytes
Authors: Kang Jione , Heart Emma , Sung Chin K.
Published: December 2017

Glucosamine induced insulin resistance in 3T3-L1 adipocytes, which was associated with a 15% decrease in cellular ATP content. To study the role of ATP depletion in insulin resistance, we employed sodium azide (NaN3) and dinitrophenol (DNP), which affect mitochondrial oxidative phosphorylation, to achieve a similar 15% ATP depletion. Unlike glucosamine, NaN3and DNP markedly increased basal glucose transport, and the increased basal glucose transport was associated with increased GLUT-1 content in the plasma membrane without changes in total GLUT-1 content. These agents, like glucosamine, did not affect the early insulin signaling that is implicated in insulin stimulation of glucose transport. In cells with a severe 40% ATP depletion, basal glucose transport was similarly elevated, and insulin-stimulated glucose transport was similar in cells with 15% ATP depletion. In these cells, however, early insulin signaling was severely diminished. These data suggest that cellular ATP depletion by glucosamine, NaN3, and DNP exerts differential effects on basal and insulin-stimulated glucose transport and that ATP depletion per se does not induce insulin resistance in 3T3-L1 adipocytes.
Adaptation of β-cell mass to substrate oversupply: enhanced function with normal gene expression
Authors: Steil Garry M. , Trivedi Nitin , Jonas Jean-Christophe , Hasenkamp Wendy M. , Sharma Arun , Bonner-Weir Susan , Weir Gordon C.
Published: December 2017

Although type 2 diabetes mellitus is associated with insulin resistance, many individuals compensate by increasing insulin secretion. Putative mechanisms underlying this compensation were assessed in the present study by use of 4-day glucose (GLC; 35% Glc, 2 ml/h) and lipid (LIH; 10% Intralipid + 20 U/ml heparin; 2 ml/h) infusions to rats. Within 2 days of beginning the infusion of either lipid or glucose, plasma glucose profiles were normalized (relative to saline-infused control rats; SAL; 0.45% 2 ml/h). During glucose infusion, plasma glucose was maintained in the normal range by an approximately twofold increase in plasma insulin and an ∼80% increase in β-cell mass. During LIH infusion, glucose profiles were also maintained in the normal range. Plasma insulin responses during feeding were doubled, and β-cell mass increased 54%. For both groups, the increase in β-cell mass was associated with increased β-cell proliferation (98% increase during GLC and 125% increase during LIH). At the end of the 4-day infusions, no significant changes were observed in islet-specific gene transcription (i.e., the expression of islet hormone genes, glucose metabolism genes, and insulin transcription factors were unaffected). Two days after termination of the infusions, the glucose-stimulated plasma insulin response was increased ∼67% in glucose-infused animals. No sustained effect on insulin secretory capacity was observed in the LIH animals. The increase in plasma insulin response after glucose infusion was achieved in the absence of any change in insulin clearance. We conclude that, in rats, an increase in insulin demand after an increase in glucose appearance or free fatty acid leads to an increase in β-cell mass, mediated in part by an increase in β-cell proliferation, and that these compensatory changes lead to increased insulin secretion, normal plasma glucose levels, and the maintenance of normal islet gene expression.
Increased concentration of tracee affects estimates of muscle protein synthesis
Authors: Caso Giuseppe , Ford G. Charles , Nair K. Sreekumaran , Vosswinkel James A. , Garlick Peter J. , McNurlan Margaret A.
Published: December 2017

Muscle protein synthesis was measured by infusion ofl-[2H5]phenylalanine in two groups of anesthetized dogs, before and during infusion of insulin with euaminoacidemia, and with differing concentrations of unlabeled phenylalanine (tracee). With the infusion of insulin, muscle protein synthesis increased 39 ± 12% based on phenylalanyl-tRNA. Calculation with plasma phenylalanine enrichment overestimated insulin stimulation by 40% (56 ± 12 vs. 39 ± 12%). Raising the concentration of plasma phenylalanine twofold during infusion of insulin further increased the apparent stimulation of muscle protein synthesis based on plasma relative to phenylalanyl-tRNA by 225% (65 ± 19 vs. 20 ± 14%, P < 0.001). In both experiments, the stimulation of synthesis rates calculated from phenylalanine enrichment within the muscle was closer to that from phenylalanyl-tRNA (48 ± 19%, experiment 1; 30 ± 14%, experiment 2). Results indicate that the enrichment of a labeled amino acid within plasma and tissue amino acid pools is affected by the concentration of tracee infused. Increasing the concentration of tracee overestimates the insulin-mediated stimulation of muscle protein synthesis when amino acid pools other than aminoacyl-tRNA are used as the precursor enrichment.
Natural abundance deuterium and 18-oxygen effects on the precision of the doubly labeled water method
Authors: Horvitz Micah A. , Schoeller Dale A.
Published: December 2017

The doubly labeled water method for measuring total energy expenditure is subject to error from natural variations in the background2H and18O in body water. There is disagreement as to whether the variations in background abundances of the two stable isotopes covary and what relative doses of2H and18O minimize the impact of variation on the precision of the method. We have performed two studies to investigate the amount and covariance of the background variations. These were a study of urine collected weekly from eight subjects who remained in the Madison, WI locale for 6 wk and frequent urine samples from 14 subjects during round-trip travel to a locale ≥500 miles from Madison, WI. Background variation in excess of analytical error was detected in six of the eight nontravelers, and covariance was demonstrated in four subjects. Background variation was detected in all 14 travelers, and covariance was demonstrated in 11 subjects. The median slopes of the regression lines of δ2H vs. δ18O were 6 and 7, respectively. Modeling indicated that2H and18O doses yielding a 6:1 ratio of final enrichments should minimize this error introduced to the doubly labeled water method.
Increased expression of GPI-specific phospholipase D in mouse models of type 1 diabetes
Authors: Deeg Mark A. , Bowen Rosario F. , Williams Monet D. , Olson L. Karl , Kirk Elizabeth A. , LeBoeuf Renée C.
Published: December 2017

Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is a high-density lipoprotein-associated protein. However, the tissue source(s) for circulating GPI-PLD and whether serum levels are regulated are unknown. Because the diabetic state alters lipoprotein metabolism, and liver and pancreatic islets are possible sources of GPI-PLD, we hypothesized that GPI-PLD levels would be altered in diabetes. GPI-PLD serum activity and liver mRNA were examined in two mouse models of type 1 diabetes, a nonobese diabetic (NOD) mouse model and low-dose streptozotocin-induced diabetes in CD-1 mice. With the onset of hyperglycemia (2- to 5-fold increase over nondiabetic levels), GPI-PLD serum activity and liver mRNA increased 2- to 4-fold in both models. Conversely, islet expression of GPI-PLD was absent as determined by immunofluorescence. Insulin may regulate GPI-PLD expression, because insulin treatment of diabetic NOD mice corrected the hyperglycemia along with reducing serum GPI-PLD activity and liver mRNA. Our data demonstrate that serum GPI-PLD levels are altered in the diabetic state and are consistent with liver as a contributor to circulating GPI-PLD.
Zinc stimulates the activity of the insulin- and nutrient-regulated protein kinase mTOR
Authors: Lynch Christopher J. , Patson Brian J. , Goodman Stacy A. , Trapolsi Donald , Kimball Scot R.
Published: December 2017

Recent studies indicate that zinc activates p70 S6 kinase (p70S6k) by a mechanism involving phosphatidylinositol 3-kinase (PI 3-kinase) and Akt (protein kinase B). Here it is shown that phenanthroline, a zinc and heavy metal chelator, inhibited both amino acid- and insulin-stimulated phosphorylation of p70S6k. Both amino acid and insulin activations of p70S6kinvolve a rapamycin-sensitive step that involves the mammalian target of rapamycin (mTOR, also known as FRAP and RAFT). However, in contrast to insulin, amino acids activate p70S6kby an unknown PI 3-kinase- and Akt-independent mechanism. Thus the effects of chelator on amino acid activation of p70S6kwere surprising. For this reason, we tested the hypothesis that zinc directly regulates mTOR activity, independently of PI 3-kinase activation. In support of this, basal and amino acid stimulation of p70S6kphosphorylation was increased by zinc addition to the incubation media. Furthermore, the protein kinase activities of mTOR immunoprecipitated from rat brain lysates were stimulated two- to fivefold by 10–300 μM Zn2+in the presence of an excess of either Mn2+or Mg2+, whereas incubation with 1,10-phenanthroline had no effect. These findings indicate that Zn2+regulates, but is not absolutely required for, mTOR protein kinase activity. Zinc also stimulated a recombinant human form of mTOR. The stimulatory effects of Zn2+were maximal at ∼100 μM but decreased and became inhibitory at higher physiologically irrelevant concentrations. Micromolar concentrations of other divalent cations, Ca2+, Fe2+, and Mn2+, had no effect on the protein kinase activity of mTOR in the presence of excess Mg2+. Our results and the results of others suggest that zinc acts at multiple steps in amino acid- and insulin cell-signaling pathways, including mTOR, and that the additive effects of Zn2+on these steps may thereby promote insulin and nutritional signaling.
Role of the human V1vasopressin receptor COOH terminus in internalization and mitogenic signal transduction
Authors: Thibonnier Marc , Plesnicher Christine L. , Berrada Karim , Berti-Mattera Liliana
Published: December 2017

We studied the role played by the intracellular COOH-terminal region of the human arginine vasopressin (AVP) V1-vascular receptor (V1R) in ligand binding, trafficking, and mitogenic signal transduction in Chinese hamster ovary cells stably transfected with the human AVP receptor cDNA clones that we had isolated previously. Truncations, mutations, or chimeric alterations of the V1R COOH terminus did not alter ligand binding, but agonist-induced V1R internalization and recycling were reduced in the absence of the proximal region of the V1R COOH terminus. Coupling to phospholipase C was altered as a function of the COOH-terminal length. Deletion of the proximal portion of the V1R COOH terminus or its replacement by the V2-renal receptor COOH terminus prevented AVP stimulation of DNA synthesis and progression through the cell cycle. Mutation of a kinase consensus motif in the proximal region of the V1R COOH terminus also abolished the mitogenic response. Thus the V1R cytoplasmic COOH terminus is not involved in ligand specificity but is instrumental in receptor trafficking and facilitates the interaction between the intracellular loops of the receptor, G protein, and phospholipase C. It is absolutely required for transmission of the mitogenic action of AVP, probably via a specific kinase phosphorylation site.
1,25-Dihydroxyvitamin D3downregulates the rat intestinal vitamin D3-25-hydroxylaseCYP27A
Authors: Theodoropoulos Catherine , Demers Christian , Mirshahi Ali , Gascon-Barré Marielle
Published: December 2017

The vitamin D3-25-hydroxylase CYP27A is located predominantly in liver, but its expression is also detected in extrahepatic tissues. Our aim was to evaluate the regulation of CYP27A by vitamin D3(D3) or its metabolites in rat duodena. Vitamin D-depleted rats were repleted with D3, 25-hydroxyvitamin D (25OHD), or 1,25-dihydroxyvitamin D3[1,25(OH)2D3] or acutely injected 1,25(OH)2D3to investigate the mechanisms of action of the hormone. All D3compounds led to a progressive decrease in CYP27A mRNA, with levels after D3representing 20% of that observed in D depletion. 25OHD decreased CYP27A mRNA by 55%, whereas 1,25(OH)2D3led to a 40% decrease, which was accompanied by a 31% decrease in CYP27A protein levels and an 89% decrease in enzyme activity. Peak circulating 1,25(OH)2D3concentrations were, however, the highest in D3-repleted, followed by 25OHD- and 1,25(OH)2D3-repleted animals. 1,25(OH)2D3resulted in a decrease in both CYP27A mRNA half-life and transcription rate. Our data illustrate that the intestine expresses the D3-25-hydroxylase and that the gene is highly regulated in vivo through a direct action of 1,25(OH)2D3or through the local production of D3metabolites.
Chylomicron metabolism by the isolated perfused mouse heart
Authors: Mardy Kai , Belke Darrell D. , Severson David L.
Published: December 2017

The catabolism of rat chylomicrons, labeled in their triacylglycerol (TG) component, was investigated using perfused working mouse hearts. Perfusion of mouse hearts with heparin increased lipoprotein lipase (LPL) activity in the perfusate. This heparin-releasable LPL pool remained constant over a variety of experimental conditions, including workload and fatty acid concentrations, making the mouse heart a suitable model to study chylomicron catabolism. Endothelium-bound LPL hydrolyzed radiolabeled3H-labeled chylomicrons (0.4 mM TG); the fate of LPL-derived3H-labeled fatty acids was split evenly between oxidation (production of3H2O) and esterification (incorporation into tissue lipids, mainly TG). In comparison, the oxidation of 0.4 mM [3H]palmitate complexed to albumin was fourfold greater than esterification into tissue lipids. Surprisingly, the addition of unlabeled palmitate (0.4 or 1.2 mM) to perfusions with3H-chylomicrons did not affect the fate (either oxidation or esterification) of LPL-derived3H-fatty acids. These results suggest that fatty acids produced from lipoprotein hydrolysis by the action of LPL and fatty acids from a fatty acid-albumin complex do not enter a common metabolic pool in the heart.
Amino acids do not suppress proteolysis in premature neonates
Authors: Poindexter Brenda B. , Karn Cheryl A. , Leitch Catherine A. , Liechty Edward A. , Denne Scott C.
Published: December 2017

To determine whether increased amino acid availability can reduce proteolysis in premature neonates and to assess the capacity of infants born prematurely to acutely increase the irreversible catabolism of the essential amino acids leucine (via oxidation) and phenylalanine (via hydroxylation to form tyrosine), leucine and phenylalanine kinetics were measured under basal conditions and in response to a graded infusion of intravenous amino acids (1.2 and 2.4 g · kg−1 · day−1) in clinically stable premature (∼32 wk gestation) infants in the 1st wk of life. In contrast to the dose-dependent suppression of proteolysis seen in healthy full-term neonates, the endogenous rates of appearance of leucine and phenylalanine (reflecting proteolysis) were unchanged in response to amino acids (297 ± 21, 283 ± 19, and 284 ± 31 μmol · kg−1 · h−1 for leucine and 92 ± 6, 92 ± 4, and 84 ± 7 μmol · kg−1 · h−1 for phenylalanine). Similar to full-term neonates, leucine oxidation (40 ± 5, 65 ± 6, and 99 ± 7 μmol · kg−1 · h−1) and phenylalanine hydroxylation (12 ± 1, 16 ± 1, and 20 ± 2 μmol · kg−1 · h−1) increased in a stepwise fashion in response to graded amino acids. This capacity to increase phenylalanine hydroxylation may be crucial to meet tyrosine needs when exogenous supply is limited. Finally, to determine whether amino acids stimulate glucose production in premature neonates, glucose rate of appearance was measured during each study period. In response to amino acid infusion, rates of endogenous glucose production were unchanged (and near zero).
The catecholamine response to spaceflight: role of diet and gender
Authors: Stein T. P. , Wade C. E.
Published: December 2017

Compared with men, women appear to have a decreased sympathetic nervous system (SNS) response to stress. The two manifestations where the sexual dimorphism has been the most pronounced involve the response of the SNS to fluid shifts and fuel metabolism during exercise. The objectives of this study were to investigate whether a similar sexual dimorphism was found in the response to spaceflight. To do so, we compared catecholamine excretion by male and female astronauts from two similar shuttle missions, Spacelab Life Sciences 1 (SLS1, 1991) and 2 (SLS2, 1993) for evidence of sexual dimorphism. To evaluate the variability of the catecholamine response in men, we compared catecholamine excretion from the two SLS missions against the 1996 Life and Microgravity Sciences Mission (LMS) and the 1973 Skylab missions. Results: No gender- or mission-dependent changes were found with epinephrine. Separating out the SLS1/2 data by gender shows that norepinephrine excretion was essentially unchanged with spaceflight in women (98 ± 10%; n = 3) and substantially decreased with the men (41 ± 9%; n= 4, P < 0.05). Data are a percentage of mean preflight value ± SE. Comparisons among males demonstrated significant mission effects on norepinephrine excretion. After flight, there was a transient increase in norepinephrine but no evidence of any gender-specific effects. We conclude that norepinephrine excretion during spaceflight is both mission and gender dependent. Men show the greater response, with at least three factors being involved, a response to microgravity, energy balance, and the ratio of carbohydrate to fat in the diet.
GLUT-4 translocation in skeletal muscle studied with a cell-free assay: involvement of phospholipase D
Authors: Kristiansen Søren , Nielsen Jakob N. , Bourgoin Sylvain , Klip Amira , Franco Michel , Richter Erik A.
Published: December 2017

GLUT-4-containing membranes immunoprecipitated from insulin-stimulated rat skeletal muscle produce the phospholipase D (PLD) product phosphatidic acid. In vitro stimulation of PLD in crude membrane with ammonium sulfate (5 mM) resulted in transfer of GLUT-4 (3.0-fold vs. control) as well as transferrin receptor proteins from large to small membrane structures. The in vitro GLUT-4 transfer could be blocked by neomycin (a PLD inhibitor), and neomycin also reduced insulin-stimulated glucose transport in intact incubated soleus muscles. Furthermore, protein kinase Bβ(PKBβ) was found to associate with the GLUT-4 protein and was transferred to small vesicles in response to ammonium sulfate in vitro. Finally, addition of cytosolic proteins, prepared from basal skeletal muscle, and GTP nucleotides to an enriched GLUT-4 membrane fraction resulted in in vitro transfer of GLUT-4 to small membranes (6.8-fold vs. unstimulated control). The cytosol and nucleotide-induced GLUT-4 transfer could be blocked by neomycin and N-ethylmaleimide. In conclusion, we have developed a cell-free assay that demonstrates in vitro GLUT-4 transfer. This transfer may suggest release of GLUT-4-containing vesicles from donor GLUT-4 membranes involving PLD activity and binding of PKBβto GLUT-4.
Apoprotein C-III deficiency markedly stimulates triglyceride secretion in vivo: comparison with apoprotein E
Authors: Hirano Tsutomu , Takahashi Toshihiro , Saito Shigenobu , Tajima Hiroto , Ebara Tetsu , Adachi Mitsuru
Published: December 2017

Apoprotein (apo) C-III plays an important role in the development of hypertriglyceridemia by inhibiting triglyceride (TG) removal. However, the effect of apo C-III on TG production remains unclear. We measured TG secretion rate (TGSR) in apo C-III gene-disrupted (apo C-III-null) mice to investigate the influence of this protein on TG turnover. TGSR measured by the Triton WR-1339 method was increased twofold in these mice compared with wild-type (WT) mice. Obesity was induced by the injection of gold-thioglucose (GTG), which made the WT mice hypertriglyceridemic due to a threefold increase of TGSR. However, GTG-induced obesity failed to increase TG in apo C-III-null mice, although TGSR was increased 10-fold, suggesting substantial stimulation of TG removal. Apo E-null mice were severely hypercholesterolemic but were not hypertriglyceridemic, and TGSR was rather decreased. GTG-induced obesity made these mice hypertriglyceridemic because of TG overproduction to an extent similar to that seen in WT mice. These results suggest that apo C-III deficiency potently enhances TG turnover, especially when TG production is stimulated, and that apo E deficiency is not always rate limiting for TG production.
Effect of prior exercise on glucose metabolism in trained men
Authors: Rose Adam J. , Howlett Kirsten , King Douglas S. , Hargreaves Mark
Published: December 2017

Several studies have demonstrated that oral glucose tolerance is impaired in the immediate postexercise period. A double-tracer technique was used to examine glucose kinetics during a 2-h oral glucose (75 g) tolerance test (OGTT) 30 min after exercise (Ex, 55 min at 71 ± 2% of peak O2 uptake) and 24 h after exercise (Rest) in endurance-trained men. The area under the plasma glucose curve was 71% greater in Ex than in Rest ( P = 0.01). The higher glucose response occurred even though whole body rate of glucose disappearance was 24% higher after exercise ( P = 0.04, main effect). Whole body rate of glucose appearance was 25% higher after exercise ( P = 0.03, main effect). There were no differences in total (2 h) endogenous glucose appearance (Ra e) or the magnitude of suppression of Ra e, although Ra e was higher from 15 to 30 min during the OGTT in Ex. However, the cumulative appearance of oral glucose was 30% higher in Ex ( P = 0.03, main effect). There were no differences in glucose clearance rate or plasma insulin responses between the two conditions. These results suggest that adaptations in splanchnic tissues by prior exercise facilitate greater glucose output from the splanchnic region after glucose ingestion, resulting in a greater glycemic response and, consequently, a greater rate of whole body glucose uptake.
Lipid metabolism during fasting
Authors: Jensen Michael D. , Ekberg Karin , Landau Bernard R.
Published: December 2017

These studies were conducted to understand the relationship between measures of systemic free fatty acid (FFA) reesterification and regional FFA, glycerol, and triglyceride metabolism during fasting. Indirect calorimetry was used to measure fatty acid oxidation in six men after a 60-h fast. Systemic and regional (splanchnic, renal, and leg) FFA ([3H]palmitate) and glycerol ([3H]glycerol) kinetics, as well as splanchnic triglyceride release, were measured. The rate of systemic FFA reesterification was 366 ± 93 μmol/min, which was greater ( P < 0.05) than splanchnic triglyceride fatty acid output (64 ± 6 μmol/min), a measure of VLDL triglyceride fatty acid export. The majority of glycerol uptake occurred in the splanchnic and renal beds, although some leg glycerol uptake was detected. Systemic FFA release was approximately double that usually present in overnight postabsorptive men, yet the regional FFA release rates were of the same proportions previously observed in overnight postabsorptive men. In conclusion, FFA reesterification at rest during fasting far exceeds splanchnic triglyceride fatty acid output. This indicates that nonhepatic sites of FFA reesterification are important, and that peripheral reesterification of FFA exceeds the rate of simultaneous intracellular triglyceride fatty acid oxidation.
Parenteral nutrition with lipid or glucose suppresses liver growth and response to GH in adolescent male rats
Authors: Sevette Andre , Kee Anthony J. , Carlsson Anthony R. , Baxter Robert C. , Smith Ross C.
Published: December 2017

Our aim was to investigate the effects of modifying the carbohydrate-to-lipid ratio of parenteral nutrition (PN) on body composition and the anabolic actions of insulin-like growth factor I (IGF-I) and growth hormone (GH). Adolescent male Sprague-Dawley rats were randomized to receive 7 days of GH, IGF-I (3.5 mg · kg−1 · day−1 for both) or placebo while receiving high-carbohydrate PN (CHO-PN), high-lipid PN (L-PN), or an oral diet (chow) (the PN protocols were isonitrogenous and isocaloric). PN impaired muscle growth, which was reversed by GH in the CHO-PN group only ( P < 0.03). PN increased carcass lipid ( P < 0.02), the effect being greater in the L-PN than in the CHO-PN group ( P < 0.001). Visceral lean tissue growth was significantly impaired by PN ( P < 0.001). IGF-I reversed this impairment, but GH had no effect. PN impaired the normal increase in hepatic protein and DNA ( P < 0.001) and produced liver steatosis ( P < 0.001). However, this steatosis was less in L-PN than in CHO-PN ( P < 0.001). Serum IGF-I and the acid-labile subunit (ALS) were decreased by PN ( P < 0.001) and were not affected by GH during PN treatment. However, GH significantly increased serum ALS concentrations in the chow-fed rats ( P = 0.032). In conclusion, modifying the CHO-to-L ratio of PN had no significant effect on IGF-I action, but CHO-PN increased the peripheral effect of GH. L-PN increased carcass lipid significantly and decreased hepatic steatosis. Nevertheless, PN caused significant liver steatosis and profound impairment of hepatic cell growth, which was associated with relative hepatic GH resistance.