bluuebunny/crossref_metadata_2025 huggingface dataset:
Production of soluble tumor necrosis factor receptors by human subcutaneous adipose tissue in vivo
Authors: Mohamed-Ali Vidya , Goodrick Steven , Bulmer Karen , Holly Jeffrey M. P. , Yudkin John S. , Coppack Simon W.
Published: December 2017

To investigate in vivo adipose tissue production of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and their soluble receptors: TNF receptor type I (sTNFR-I), TNF receptor type II (sTNFR-II), and IL-6 receptor (sIL-6R), we determined arteriovenous differences in their levels across abdominal subcutaneous adipose tissue in obese subjects. Subjects had a median (interquartile range) age of 44.5 (27–51.3) yr, body mass index (BMI) of 32.9 (26.0–46.6) kg/m2, and %body fat of 42.5 (28.5–51.2) %. Although there was not a significant difference in the arteriovenous concentrations of TNF-α ( P = 0.073) or sTNFR-II ( P = 0.18), the levels of sTNFR-I ( P = 0.002) were higher in the vein compared with artery, suggesting adipose tissue production of this soluble receptor. There was a significant arteriovenous difference in IL-6 ( P < 0.001) but not in its soluble receptor ( P = 0.18). There was no relationship between TNF-α levels and adiposity indexes ( rs= 0.12–0.22, P = not significant); however, levels of both its soluble receptor isomers correlated significantly with BMI and %body fat (sTNFR-I rs= 0.42–0.72, P < 0.001; sTNFR-II rs= 0.36–0.65, P < 0.05- <0.001). IL-6 levels correlated significantly with both BMI and %body fat ( rs= 0.51, P = 0.004, and rs= 0.63, P < 0.001), but sIL-6R did not. In conclusion, 1) soluble TNFR-I is produced by adipose tissue, and concentrations of both soluble isoforms correlate with the degree of adiposity, and 2) IL-6, but not its soluble receptor, is produced by adipose tissue and relates to adiposity.
Mechanisms by which insulin, associated or not with glucose, may inhibit hepatic glucose production in the rat
Authors: Guignot Ludovic , Mithieux Gilles
Published: December 2017

We investigated the intrahepatic mechanisms by which insulin, associated or not with hyperglycemia, may inhibit hepatic glucose production (HGP) in the rat. After a hyperinsulinemic euglycemic clamp in postabsorptive (PA) anesthetized rats, the 70% inhibition of HGP could be explained by a dramatic decrease in the glucose 6-phosphate (G-6- P) concentration, whereas the glucose-6-phosphatase (G-6-Pase) and glucokinase (GK) activities were unchanged. Under hyperinsulinemic hyperglycemic condition, the GK flux was increased. The G-6- P concentration was not or only weakly decreased. The inhibition of HGP involved a significant 25% inhibition of the G-6-Pase activity. Under similar conditions in fasted rats, the GK flux was very low. The suppression of G-6-Pase and HGP did not occur, despite plasma insulin and glucose concentrations similar to those in PA rats. Therefore, 1) insulin suppresses HGP in euglycemia by solely decreasing the G-6- P concentration; 2) when combining both hyperinsulinemia and hyperglycemia, the suppression of HGP involves the inhibition of the G-6-Pase activity; and 3) a sustained glucose-phosphorylation flux might be a crucial determinant in the inhibition of G-6-Pase and of HGP.
Leg free fatty acid kinetics during exercise in men and women
Authors: Burguera Bartolome , Proctor David , Dietz Niki , Guo Zengkui , Joyner Michael , Jensen Michael D.
Published: December 2017

We previously reported that epinephrine stimulates leg free fatty acid (FFA) release in men but not in women. The present studies were conducted to determine whether the same is true during exercise. Six men and six women bicycled for 90 min at 45% of peak O2 consumption, during which time systemic and leg FFA kinetics ([9,10-3H]palmitate) were measured. The catecholamine and hormonal responses to exercise were not different in men and women. The baseline systemic and leg palmitate release was 94 ± 15 vs. 114 ± 5 μmol/min and 16 ± 2 and 20 ± 3 μmol/min, respectively, in men and women [ P = nonsignificant (NS)]. Systemic and leg palmitate release increased (both P < 0.001) to 251 ± 18 vs. 212 ± 16 μmol/min and 73 ± 19 vs. 80 ± 12 μmol/min in men and women, respectively, during the last 30 min of exercise ( P = NS, men vs. women). We conclude that the systemic and leg adipose tissue lipolytic response to exercise is not different in nonobese men and women.
Bone as an ion exchange system: evidence for a pump-leak mechanism devoted to the maintenance of high bone K+
Authors: Rubinacci Alessandro , Benelli Fiorenza Dondi , Borgo Enrico , Villa Isabella
Published: December 2017

To provide evidence of active accumulation of K+ in bone extracellular fluid (BECF), electric currents driven by damaged living metatarsal bones of weanling mice, immersed in physiological media at different [K+], in the presence of blockers of the K+ channels or of the Na+-K+-ATPase inhibitor, were measured by means of a voltage-sensitive two-dimensional vibrating probe. At 4 mM extracellular K+concentration ([K+]o), an inward steady current density (7.85–38.53 μA/cm2) was recorded at the damage site, which was significantly dependent on [K+]o. At [K+]o equal to that of BECF (25 mM), current density was reduced by 76%. At [K+]o of 0 mM, the current density showed an increase, which was hindered by tetraethylammonium (TEA). Basal current density was reduced significantly after exposure to TEA or BaCl2 and was unchanged after long- term exposure to ouabain. By changing control medium with a chloride-free medium, current density was reversed. The results support the view that K+ excess in bone is maintained by a biologically active cellular system. Because the osteocyte-bone lining cell syncytium was at the origin of the current in bone, it is likely that this system controls the ionic composition of BECF.
Concordant induction of rapid in vivo pulsatile insulin secretion by recurrent punctuated glucose infusions
Authors: Pørksen Niels , Juhl Claus , Hollingdal Malene , Pincus Steve M. , Sturis Jeppe , Veldhuis Johannes D. , Schmitz Ole
Published: December 2017

Insulin is largely secreted as serial secretory bursts superimposed on basal release, insulin secretion is regulated through changes of pulse mass and frequency, and the insulin release pattern affects insulin action. Coordinate insulin release is preserved in the isolated perfused pancreas, suggesting intrapancreatic coordination. However, occurrence of glucose concentration oscillations may influence the process in vivo, as it does for ultradian oscillations. To determine if rapid pulsatile insulin release may be induced by minimal glucose infusions and to define the necessary glucose quantity, we studied six healthy individuals during brief repetitive glucose infusions of 6 and 2 mg ⋅ kg−1⋅ min−1for 1 min every10 min. The higher dose completely synchronized pulsatile insulin release at modest plasma glucose changes (∼0.3 mM = ∼5%), with large (∼100%) amplitude insulin pulses at every single glucose induction ( n = 54) at a lag time of 2 min ( P< 0.05), compared with small (10%) and rare ( n = 3) uninduced insulin excursions. The smaller glucose dose induced insulin pulses at lower significance levels and with considerable breakthrough insulin release. Periodicity shift from either 7- to 12-min or from 12- to 7-min intervals between consecutive glucose (6 mg ⋅ kg−1⋅ min−1) infusions in six volunteers revealed rapid frequency changes. The orderliness of insulin release as estimated by approximate entropy (1.459 ± 0.009 vs. 1.549 ± 0.027, P = 0.016) was significantly improved by glucose pulse induction ( n = 6; 6 mg ⋅ kg−1⋅ min−1) compared with unstimulated insulin profiles ( n = 7). We conclude that rapid in vivo oscillations in glucose may be an important regulator of pulsatile insulin secretion in humans and that the use of an intermittent pulsed glucose induction to evoke defined and recurrent insulin secretory signals may be a useful tool to unveil more subtle defects in β-cell glucose sensitivity.
Metoclopramide: a novel adjunct for improving cardiac and hepatocellular functions after trauma-hemorrhage
Authors: Jarrar Doraid , Wang Ping , Song Grace Y. , Knöferl Markus W. , Cioffi William G. , Bland Kirby I. , Chaudry Irshad H.
Published: December 2017

Although metoclopramide (MCP) administration after trauma-hemorrhage restores the depressed immune functions, it remains unknown whether this agent has any salutary effects on the depressed cardiovascular and hepatocellular functions under those conditions. Adult male Sprague-Dawley rats underwent a midline laparotomy (i.e., induction of soft-tissue trauma) and were then bled to and maintained at a mean arterial pressure (MAP) of 40 mmHg until 40% of the maximal shed blood volume was returned in the form of Ringer lactate (RL). The rats were then resuscitated with four times the shed blood volume in the form of RL over 60 min. MCP (2 mg/kg body wt) or vehicle was administered subcutaneously at the end of resuscitation. At 24 h after resuscitation, cardiac index and hepatocellular function (i.e., the maximum velocity and the overall efficiency of indocyanine green clearance) were determined. Plasma levels of interleukin (IL)-6 and prolactin were also assayed. The results indicate that treatment with MCP after trauma-hemorrhage and resuscitation significantly improved the depressed cardiac output and hepatocellular function. Furthermore, MCP administration significantly increased circulating levels of prolactin and decreased the plasma levels of the proinflammatory cytokine IL-6. Thus, administration of MCP, which increased prolactin secretion, appears to be a useful adjunct for restoring the depressed cardiac and hepatocellular functions and downregulating inflammatory cytokine release after trauma and hemorrhagic shock.
Reduced synthesis of muscle proteins in chronic renal failure
Authors: Adey Deborah , Kumar Rajiv , McCarthy James T. , Nair K. Sreekumaran
Published: December 2017

Muscle wasting and weakness occur frequently in patients with chronic renal failure. The mechanism(s) by which these abnormalities occur is unclear. We hypothesized that such findings were due to defective muscle protein synthesis. We measured synthetic rates of mixed muscle proteins, myosin heavy chain, and mitochondrial proteins in serial muscle biopsy samples during a continuous infusion ofl[1-13C]leucine from 12 patients with chronic renal failure and 10 healthy control subjects under identical study conditions. Patients with chronic renal failure have significantly lower synthetic rates of mixed muscle proteins and myosin heavy chain (27 and 37% reductions, respectively, P < 0.05 and P < 0.02). Significant declines in the synthetic rates of muscle mitochondrial protein (27%) ( P < 0.05), muscle cytochrome c-oxidase activity (42%) ( P < 0.007), and citrate synthase (27%) ( P < 0.007) were also observed in patients with chronic renal failure. The synthetic rates of muscle proteins and activity of mitochondrial enzymes were negatively correlated to the severity of renal failure. These results indicate that in chronic renal failure there is a decrease in the synthesis of muscle contractile and mitochondrial proteins and a decrease in muscle mitochondrial oxidative enzymes. Reduced synthetic rate of several muscle proteins is the likely biochemical basis of muscle loss and muscle weakness in people with chronic renal failure.
Sensitivity of CPT I to malonyl-CoA in trained and untrained human skeletal muscle
Authors: Starritt Emma C. , Howlett Richard A. , Heigenhauser George J. F. , Spriet Lawrence L.
Published: December 2017

The present study examined the sensitivity of carnitine palmitoyltransferase I (CPT I) activity to its inhibitor malonyl-CoA (M-CoA), and simulated metabolic conditions of rest and exercise, in aerobically trained and untrained humans. Maximal CPT I activity was measured in mitochondria isolated from resting human skeletal muscle. Mean CPT I activity was 492.8 ± 72.8 and 260.8 ± 33.6 μmol ⋅ min−1⋅ kg wet muscle−1in trained and untrained subjects, respectively (pH 7.0, 37°C). The sensitivity to M-CoA was greater in trained muscle; the IC50for M-CoA was 0.17 ± 0.04 and 0.49 ± 0.17 μM in trained and untrained muscle, respectively. The presence of acetyl-CoA, free coenzyme A (CoASH), and acetylcarnitine, in concentrations simulating rest and exercise conditions did not release the M-CoA-induced inhibition of CPT I activity. However, CPT I activity was reduced at pH 6.8 vs. pH 7.0 in both trained and untrained muscle in the presence of physiological concentrations of M-CoA. The results of this study indicate that aerobic training is associated with an increase in the sensitivity of CPT I to M-CoA. Accumulations of acetyl-CoA, CoASH, and acetylcarnitine do not counteract the M-CoA-induced inhibition of CPT I activity. However, small decreases in pH produce large reductions in the activity of CPT I and may contribute to the decrease in fat metabolism that occurs during moderate and intense aerobic exercise intensities.
Protein kinase C modulates insulin action in human skeletal muscle
Authors: Cortright Ronald N. , Azevedo John L. , Zhou Qian , Sinha Madhur , Pories Walter J. , Itani Samar I. , Dohm G. Lynis
Published: December 2017

There is good evidence from cell lines and rodents that elevated protein kinase C (PKC) overexpression/activity causes insulin resistance. Therefore, the present study determined the effects of PKC activation/inhibition on insulin-mediated glucose transport in incubated human skeletal muscle and primary adipocytes to discern a potential role for PKC in insulin action. Rectus abdominus muscle strips or adipocytes from obese, insulin-resistant, and insulin-sensitive patients were incubated in vitro under basal and insulin (100 nM)-stimulated conditions in the presence of GF 109203X (GF), a PKC inhibitor, or 12-deoxyphorbol 13-phenylacetate 20-acetate (dPPA), a PKC activator. PKC inhibition had no effect on basal glucose transport. GF increased ( P < 0.05) insulin-stimulated 2-deoxyglucose (2-DOG) transport approximately twofold above basal. GF plus insulin also increased ( P < 0.05) insulin receptor tyrosine phosphorylation 48% and phosphatidylinositol 3-kinase (PI 3-kinase) activity ∼50% ( P< 0.05) vs. insulin treatment alone. Similar results for GF on glucose uptake were observed in human primary adipocytes. Further support for the hypothesis that elevated PKC activity is related to insulin resistance comes from the finding that PKC activation by dPPA was associated with a 40% decrease ( P < 0.05) in insulin-stimulated 2-DOG transport. Incubation of insulin-sensitive muscles with GF also resulted in enhanced insulin action (∼3-fold above basal). These data demonstrate that certain PKC inhibitors augment insulin-mediated glucose uptake and suggest that PKC may modulate insulin action in human skeletal muscle.
Determination of protein synthesis in human ileum in situ by continuous [1-13C]leucine infusion
Authors: Rittler Peter , Demmelmair Hans , Koletzko Berthold , Schildberg Friedrich W. , Hartl Wolfgang H.
Published: December 2017

Efficient protein synthesis plays an important role in the physiology and pathophysiology of the human gastrointestinal tract. Because of methodological restrictions, no studies on ileal protein synthesis in situ are available in humans. We used advanced mass spectrometry techniques (capillary gas chromatography/combustion isotope ratio mass spectrometry) to determine directly the incorporation rate of [1-13C]leucine into ileal mucosal protein in control subjects and postoperative patients. All subjects had an ileostomy, which allowed easy access to the ileal mucosa. To examine changes in ileal protein synthesis during prolonged isotope infusion (0.16 μmol ⋅ kg−1 ⋅ min− 1, 9.6 μmol/kg prime), studies were performed over a 10-h period. Mucosal biopsies were performed after 3, 6, and 10 h of infusion. Protein synthesis was calculated separately between hour 3 and hour 6 ( period 1) and hour 6 and hour 10 ( period 2). Control subjects demonstrated an ileal protein fractional synthetic rate of 0.62 ± 0.06%/h in period 1 and of 0.52 ± 0.08%/h in period 2 (not significant). In postsurgical subjects, ileal protein synthesis was significantly higher (1.11 ± 0.14%/h in period 1, P < 0.01 vs. controls in period 1) but declined markedly in period 2(0.39 ± 0.13, P < 0.01 vs. period 1 after surgery). The rate of protein synthesis in the small bowel of control subjects is, thus far, among the lowest measured in mammals and reflects the comparably slow turnover of human ileal mucosa. Postoperative disturbances of gut integrity lead to an accelerated anabolic response. During prolonged isotope infusion, stimulated protein synthesis declines because of diurnal variations or is erroneously reduced by tracer loss due to an accelerated cell turnover.
Influences of IGF-I gene disruption on the cellular profile of the diaphragm
Authors: Fournier Mario , Lewis Michael I.
Published: December 2017

The impact of a targeted disruption of the Igf1 gene, encoding the insulin-like growth factor I (IGF-I), on diaphragm (DIA) cellularity was studied in 2-mo-old homozygous mutant [IGF-I(−/−)] mice and their wild-type [WT; i.e., IGF-I(+/+)] littermates. DIA fiber types were classified histochemically. DIA fiber cross-sectional areas (CSA) were determined from digitized muscle sections, and fiber succinate dehydrogenase (SDH) activity was determined histochemically using a microdensitometric procedure. An acidic ATPase reaction was used to visualize capillaries. Myosin heavy chain (MyHC) isoforms were identified by SDS-PAGE, and their proportions were determined by scanning densitometry. The body weight of IGF-I(−/−) animals was 32% that of WT littermates. DIA fiber type proportions were unchanged between the groups. The CSAs of types I, IIa, and IIx DIA fibers of IGF-I(−/−) mutants were 63, 68, and 65%, respectively, those of WT animals ( P < 0.001). The DIA thickness and the number of fibers spanning its entire thickness were reduced by 36 and 25%, respectively, in IGF-I(−/−) mice ( P < 0.001). SDH activity was significantly increased in all three types of DIA fibers of IGF-I(−/−) mutants ( P< 0.05). The number of capillaries per fiber was reduced ∼30% in IGF-I(−/−) animals, whereas the capillary density was preserved. The proportions of MyHC isoforms were similar between the groups. Muscle hypoplasia likely reflects the importance of IGF-I on cell proliferation, differentiation, and apoptosis (alone or in combination) during development, although reduced cell size highlights the importance of IGF-I on rate and/or maintenance of DIA fiber growth in the postnatal state. Reduced capillarity may result from both direct and indirect influences on angiogenesis. Improved oxidative capacity likely reflects DIA compensatory mechanisms in IGF-I(−/−) mutants.
Functional comparison of the role of dynamin 2 splice variants on GLUT-4 endocytosis in 3T3L1 adipocytes
Authors: Kao Aimee W. , Yang Chunmei , Pessin Jeffrey E.
Published: December 2017

Previously, we reported that expression of a dominant-interfering neuronal-specific dynamin 1 (K44A/dynamin 1) inhibited the plasma membrane internalization of GLUT-4 in 3T3L1 adipocytes (15). To investigate the role of the ubiquitously expressed isoform of dynamin, dynamin 2, on adipocyte GLUT-4 internalization, and to determine whether dynamin splice variants have functional specificity, we expressed each of the four dynamin 2 isoforms (aa, ab, ba, and bb) as either wild-type proteins or GTPase-defective mutants. When expressed as enhanced green fluorescent protein (EGFP) fusions, these isoforms were found to have overlapping subcellular distributions being localized throughout the cell cytoplasm, on punctate vesicles and in a perinuclear compartment. This distribution was qualitatively similar to that of endogenous dynamin 2 and overlapped with GLUT-4 in the basal state. Expression of wild-type dynamin 2 isoforms had no effect on the basal or insulin-stimulated distribution of GLUT-4; however, expression of the dominant-interfering dynamin 2 mutants inhibited GLUT-4 endocytosis. These data demonstrate that dynamin 2 is required for GLUT-4 endocytosis in 3T3L1 adipocytes and suggest that, relative to GLUT-4 trafficking, the dynamin 2 splice variants have overlapping functions and are probably not responsible for mediating distinct GLUT-4 budding events.
Subdivisions of subcutaneous abdominal adipose tissue and insulin resistance
Authors: Kelley David E. , Thaete F. Leland , Troost Fred , Huwe Trina , Goodpaster Bret H.
Published: December 2017

Whereas truncal (central) adiposity is strongly associated with the insulin resistant metabolic syndrome, it is uncertain whether this is accounted for principally by visceral adiposity (VAT). Several recent studies find as strong or stronger association between subcutaneous abdominal adiposity (SAT) and insulin resistance. To reexamine the issue of truncal adipose tissue depots, we performed cross-sectional abdominal computed tomography, and we undertook the novel approach of partitioning SAT into the plane superficial to the fascia within subcutaneous adipose tissue (superficial SAT) and that below this fascia (deep SAT), as well as measurement of VAT. Among 47 lean and obese glucose-tolerant men and women, insulin-stimulated glucose utilization, measured by euglycemic clamp, was strongly correlated with both VAT and deep SAT ( r = −0.61 and −0.64, respectively; both P < 0.001), but not with superficial SAT ( r = −0.29, not significant). Also, VAT and deep SAT followed a highly congruent pattern of associations with glucose and insulin area under the curve (75-g oral glucose tolerance test), mean arterial blood pressure, apoprotein-B, high-density lipoprotein cholesterol, and triglyceride. Superficial SAT had markedly weaker association with all these parameters and instead followed the pattern observed for thigh subcutaneous adiposity. We conclude that there are two functionally distinct compartments of adipose tissue within abdominal subcutaneous fat and that the deep SAT has a strong relation to insulin resistance.
Endotoxin-induced decrease in muscle protein synthesis is associated with changes in eIF2B, eIF4E, and IGF-I
Authors: Lang Charles H. , Frost Robert A. , Jefferson Leonard S. , Kimball Scot R. , Vary Thomas C.
Published: December 2017

The present study examined potential mechanisms contributing to the inhibition of protein synthesis in skeletal muscle after administration of endotoxin (LPS). Rats implanted with vascular catheters were injected intravenously with a nonlethal dose of Escherichia coli LPS, and samples were collected at 4 and 24 h thereafter; pair-fed control animals were also included. The rate of muscle (gastrocnemius) protein synthesis in vivo was reduced at both time points after LPS administration. LPS did not alter tissue RNA content, but the translational efficiency was consistently reduced at both time points. To identify mechanisms responsible for regulating translation, we examined several eukaryotic initiation factors (eIFs). The content of eIF2α or the amount of eIF2α in the phosphorylated form did not change in response to LPS. eIF2B activity was decreased in muscle 4 h post-LPS but activity returned to control values by 24 h. A decrease in the relative amount of eIF2Bα protein was not responsible for the LPS-induced reduction in eIF2B activity. LPS also markedly altered the distribution of eIF4E in muscle. Compared with control values, LPS-treated rats demonstrated 1) a transient increase in binding of the translation repressor 4E-binding protein-1 (4E-BP1) with eIF4E, 2) a transient decrease in the phosphorylated γ-form of 4E-BP1, and 3) a sustained decrease in the amount of eIF4G associated with eIF4E. LPS also decreased insulin-like growth factor (IGF) I protein and mRNA expression in muscle at both times. A significant linear relationship existed between muscle IGF-I and the rate of protein synthesis or the amount of eIF4E bound to eIF4G. In summary, these data suggest that LPS impairs muscle protein synthesis, at least in part, by decreasing translational efficiency, resulting from an impairment in translation initiation associated with alterations in both eIF2B activity and eIF4E availability.
Insulin-like growth factor (IGF)-binding proteins: interactions with IGFs and intrinsic bioactivities
Authors: Baxter Robert C.
Published: December 2017

The insulin-like growth factor (IGF)-binding proteins (IGFBPs) are a family of six homologous proteins with high binding affinity for IGF-I and IGF-II. Information from NMR and mutagenesis studies is advancing knowledge of the key residues involved in these interactions. IGF binding may be modulated by IGFBP modifications, such as phosphorylation and proteolysis, and by cell or matrix association of the IGFBPs. All six IGFBPs have been shown to inhibit IGF action, but stimulatory effects have also been established for IGFBP-1, -3, and -5. These generally involve a decrease in IGFBP affinity and may require cell association of the IGFBP, but precise mechanisms are unknown. The same three IGFBPs have well established effects that are independent of type I IGF receptor signaling. IGFBP-1 exerts these effects by signaling through α5β1-integrin, whereas IGFBP-3 and -5 may have specific cell-surface receptors with serine kinase activity. The regulation of cell sensitivity to inhibitory IGFBP signaling may play a role in the growth control of malignant cells.
Ability of insulin to modulate hepatic glucose production in aging rats is impaired by fat accumulation
Authors: Gupta Gaurav , Cases Jane A. , She Li , Ma Xiao-Hui , Yang Xiao-Man , Hu Meizu , Wu Jeanie , Rossetti Luciano , Barzilai Nir
Published: December 2017

Increased total fat mass (FM) and visceral fat (VF) may account in part for age-associated decrease in hepatic insulin action. This study determined whether preventing the changes in body fat distribution abolished this defect throughout aging. We studied the F1hybrid of Brown Norway-Fischer 344 rats ( n = 29), which we assigned to caloric restriction (CR) or fed ad libitum (AL). CR (55% of the calories consumed by AL) was initiated and used at 2 mo to prevent age-dependent increases in FM and VF. AL rats were studied at 2, 8, and 20 mo; CR rats were studied at 8 and 20 mo. VF and FM remained unchanged throughout aging in CR rats. AL-fed rats at 8 and 20 mo had over fourfold higher FM and VF compared with both CR groups. Insulin clamp studies (3 mU ⋅ kg−1⋅ min−1with somatostatin) were performed to assess hepatic insulin sensitivity. Prevention of fat accretion resulted in a marked improvement in insulin action in the suppression of hepatic glucose production (HGP) (6.3 ± 0.3 and 7.2 ± 1.2 mg ⋅ kg−1⋅ min−1in 8- and 20-mo CR rats vs. 8.3 ± 0.5 and 10.8 ± 0.9 mg ⋅ kg−1⋅ min−1in 8- and 20-mo AL rats, respectively). The rate of gluconeogenesis (by enrichment of hepatic uridine diphosphate glucose and phospho enolpyruvate pools by [14C]lactate) was unchanged in all groups. The improvement in hepatic insulin action in the CR group was mostly due to effective suppression of glycogenolysis (4.4 ± 0.3 and 4.9 ± 0.3 mg ⋅ kg−1⋅ min−1in 8- and 20-mo CR rats vs. 5.8 ± 0.6 and 8.2 ± 1.0 mg ⋅ kg−1⋅ min−1in 8- and 20-mo AL rats, respectively). The results demonstrated the preservation of hepatic insulin action in aging CR rats. Therefore, body fat and its distribution are major determinants of age-associated hepatic insulin resistance.
Effects of simulated hyperglycemia, insulin, and glucagon on endothelial nitric oxide synthase expression
Authors: Ding Yaoxian , Vaziri Nosratola D. , Coulson Richard , Kamanna Vaijinath S. , Roh Daeyoung D.
Published: December 2017

Diabetes is associated with endothelial dysfunction and increased risk of hypertension, cardiovascular disease, and renal complications. Earlier studies have revealed that hyperglycemia impairs nitric oxide (NO) production and diabetes causes endothelial dysfunction in humans and experimental animals. This study was designed to test the effects of altered concentrations of glucose, insulin, and glucagon, the principal variables in types I and II diabetes, on NO production and endothelial NO synthase (eNOS) expression in cultured human coronary endothelial cells. Cultured endothelial cells were incubated in the presence of glucose at either normal (5.6 mM) or high (25 mM) concentrations for 7 days. The rates of basal and bradykinin-stimulated NO production (nitrate + nitrite) and eNOS protein expression (Western blot) were then determined at the basal condition and in the presence of insulin (10−8and 10−7M), glucagon (10−8and 10−7M), or both. Incubation with a high-glucose concentration for 7 days significantly downregulated, whereas insulin significantly upregulated, basal and bradykinin-stimulated NO production and eNOS expression in cultured endothelial cells. The stimulatory action of insulin was mitigated by high-glucose concentration and abolished by cotreatment of cells with glucagon. Thus hyperglycemia, insulinopenia, and hyperglucagonemia, which frequently coexist in diabetes, can work in concert to suppress NO production by human coronary artery endothelial cells.
Weight loss in postmenopausal obesity: no adverse alterations in body composition and protein metabolism
Authors: Gallagher Dympna , Kovera Albert J. , Clay-Williams Gaynelle , Agin Denise , Leone Patricia , Albu Jeanine , Matthews Dwight E. , Heymsfield Steven B.
Published: December 2017

We sought to determine if decrements in the mass of fat-free body mass (FFM) and other lean tissue compartments, and related changes in protein metabolism, are appropriate for weight loss in obese older women. Subjects were 14 healthy weight-stable obese (BMI ≥30 kg/m2) postmenopausal women >55 yr who participated in a 16-wk, 1,200 kcal/day nutritionally complete diet. Measures at baseline and 16 wk included FFM and appendicular lean soft tissue (LST) by dual-energy X-ray absorptiometry; body cell mass (BCM) by 40K whole body counting; total body water (TBW) by tritium dilution; skeletal muscle (SM) by whole body MRI; and fasting whole body protein metabolism through l-[1-13C]leucine kinetics. Mean weight loss (±SD) was 9.6 ± 3.0 kg ( P < 0.0001) or 10.7% of initial body weight. FFM decreased by 2.1 ± 2.6 kg ( P = 0.006), or 19.5% of weight loss, and did not differ from that reported (2.3 ± 0.7 kg). Relative losses of SM, LST, TBW, and BCM were consistent with reductions in body weight and FFM. Changes in [13C]leucine flux, oxidation, and synthesis rates were not significant. Follow-up of 11 subjects at 23.7 ± 5.7 mo showed body weight and fat mass to be below baseline values; FFM was nonsignificantly reduced. Weight loss was accompanied by body composition and protein kinetic changes that appear appropriate for the magnitude of body mass change, thus failing to support the concern that diet-induced weight loss in obese postmenopausal women produces disproportionate LST losses.
Longitudinal changes in growth hormone secretory process irregularity assessed transpubertally in healthy boys
Authors: Pincus Steven M. , Veldhuis Johannes D. , Rogol Alan D.
Published: December 2017

Clarifying the time evolution, and underlying neuroendocrine regulation, of hormone secretion during puberty is of pivotal importance both physiologically and clinically. We sought to determine whether clinical growth and elevated growth hormone (GH) release in pubertal boys are associated with shifts in the irregularity of GH secretory patterns. We studied GH release in 23 healthy boys longitudinally at ∼4-mo intervals over a 6-yr period throughout puberty, by repetitive blood sampling at 20-min intervals for 24 h on each study date. To quantify serial irregularity in the GH profiles, we utilized approximate entropy (ApEn), a scale- and model-independent quantification of the extent of sequential “randomness.” Complementary statistical analyses establish that on a per-subject basis, serum GH concentration-time series show greatest secretory disorderliness (maximal ApEn) in prepuberty and mid-to-late puberty, followed by a steep decline in ApEn to maximal orderliness in postpubertal adolescence ( P< 0.0001, ANOVA). Pooling all subject comparisons, we observed a persistent positive correlation between ApEn and growth velocity (GrVel), Pearson r = 0.467 ( P < < 10−10). Moreover, in general, ApEn(GH) preceded GrVel evolution, with a time frame lead of 4–8 mo providing the most pronounced correlations between ApEn and GrVel. In the setting of low postpubertal growth, per-subject ApEn values fell to approximately one-half of maximal ApEn values and, on average, were in the 13th percentile from minimal ( P < < 10−10) for fully mature boys. Thus, in a longitudinal transpubertal analysis, greater irregularity in GH secretion corresponds to greater linear growth in boys, which culminates in highly regular GH secretory dynamics after sexual maturity. In addition to clinical utility, there may be added experimental merit in knowing that GH dynamics typically predict accelerated linear growth in 4–8 mo.
Glucose transporters and transport kinetics in retinoic acid-differentiated T47D human breast cancer cells
Authors: Rivenzon-Segal Dalia , Rushkin Edna , Polak-Charcon Sylvie , Degani Hadassa
Published: December 2017

The rates of glucose transport and of glycolysis and the expression of the glucose transporters GLUT-1 through GLUT-4 were measured in T47D human breast cancer cells that underwent differentiation by retinoic acid. Glucose transport was found to be the rate-limiting step of glycolysis in control and differentiated cells. The transporters GLUT-1, GLUT-3, and GLUT-4 were present in the cell membrane and in the cytoplasm, and GLUT-2 was present solely in the cytoplasm. Differentiation led to a reduction in GLUT-1 and to an increase in cytoplasmic GLUT-2 and GLUT-3 with no change in GLUT-4. Differentiation also caused a reduction in the maximal velocity of glucose transport by ∼40% without affecting the Michaelis-Menten constant of glucose transport. These changes did not alter the steady-state concentration of the phosphate metabolites regulating cell energetics but increased the content of phospholipid breakdown phosphodiesters. In conclusion, differentiation of human breast cancer cells appears to be associated with decreased glycolysis by a mechanism that involves a reduction in GLUT-1 and a slowdown of glucose transport.
Resting energy expenditure-fat-free mass relationship: new insights provided by body composition modeling
Authors: Wang Zimian , Heshka Stanley , Gallagher Dympna , Boozer Carol N. , Kotler Donald P. , Heymsfield Steven B.
Published: December 2017

The relationship between resting energy expenditure (REE) and metabolically active fat-free mass (FFM) is a cornerstone in the study of physiological aspects of body weight regulation and human energy requirements. Important questions, however, remain unanswered regarding the observed linear REE-FFM association in adult humans. This led us to develop a series of REE-body composition models that provide insights into the widely used simple linear REE-FFM prediction model derived experimentally in adult humans. The new models suggest that the REE-FFM relationship in mammals as a whole is curvilinear, that a segment of this function within a FFM range characteristic of adult humans can be fit with a linear equation almost identical to that observed from a composite review of earlier human studies, and that mammals as a whole exhibit a decrease in the proportion of FFM as high metabolic rate organs with greater FFM. The present study thus provides a new approach for examining REE-FFM relationships, advances in a quantitative manner previously observed albeit incompletely formulated REE-body composition associations, and identifies areas in need of additional research.
Increased thermogenic response to food and fat oxidation in female athletes: relationship withV˙o2 max
Authors: López Pilar , Ledoux Marielle , Garrel Dominique R.
Published: December 2017

The thermogenic response to food (TRF) and substrate oxidation were studied in 12 endurance-trained and 13 untrained female subjects. Energy expenditure and substrate oxidation were calculated by indirect calorimetry before and for 6 h after an oral test meal and after the same meal given intragastrically on a separate occasion. The TRF was calculated after the oral meal, the obligatory component after the intragastric meal (OTRF), and the facultative component from the difference between the two. V˙o2 maxwas measured on a treadmill and body composition by underwater weighing. The TRF and OTRF were significantly higher in trained than in untrained subjects: 223 ± 63 vs. 185 ± 50 kJ/6 h ( P< 0.03) and 174 ± 38 vs. 131 ± 37 kJ/6 h ( P < 0.01) for the TRF and OTRF in trained vs. untrained subjects, respectively. Multiple regression analysis showed that maximum O2consumption (V˙o2 max), but not percentage of body fat, was significantly related to OTRF ( r =0.68, P < 0.01). Trained subjects had higher fatty acid oxidation than untrained subjects before (0.6 vs. 0.4 mg · kg−1· min−1, P < 0.05) and after the oral meal (13 ± 6 vs. 8 ± 4 g/6 h P < 0.05). These results demonstrate that 1) TRF is higher in trained than in untrained women; 2) this is due to a higher cost of nutrient digestion, absorption and storage; 3) the difference is related to higher V˙o2 max; and 4) fatty acid oxidation is greater in trained women in both the postabsorptive and postprandial states. These observations suggest that endurance training induces metabolic changes that favor leanness.
UCP-3 expression in skeletal muscle: effects of exercise, hypoxia, and AMP-activated protein kinase
Authors: Zhou Min , Lin Bao-Zhen , Coughlin Sean , Vallega Gino , Pilch Paul F.
Published: December 2017

Uncoupling protein 3 (UCP-3), a member of the mitochondrial transporter superfamily, is expressed primarily in skeletal muscle where it may play a role in altering metabolic function under conditions of fuel depletion caused, for example, by fasting and exercise. Here, we show that treadmill running by rats rapidly (30 min) induces skeletal muscle UCP-3 mRNA expression (sevenfold after 200 min), as do hypoxia and swimming in a comparably rapid and substantial fashion. The expression of the mitochondrial transporters, carnitine palmitoyltransferase 1 and the tricarboxylate carrier, is unaffected under these conditions. Hypoxia and exercise-mediated induction of UCP-3 mRNA result in a corresponding four- to sixfold increase in rat UCP-3 protein. We treated extensor digitorum longus (EDL) muscle with 5′-amino-4-imidazolecarboxamide ribonucleoside (AICAR), a compound that activates AMP-activated protein kinase (AMPK), an enzyme known to be stimulated during exercise and hypoxia. Incubation of rat EDL muscle in vitro for 30 min with 2 mM AICAR causes a threefold increase in UCP-3 mRNA and a 1.5-fold increase of UCP-3 protein compared with untreated muscle. These data are consistent with the notion that activation of AMPK, presumably as a result of fuel depletion, rapidly regulates UCP-3 gene expression.
Functional parathyroid hormone receptors are present in an umbilical vein endothelial cell line
Authors: Isales Carlos M. , Sumpio Bauer , Bollag Roni J. , Zhong Qing , Ding Ke-Hong , Du Wei , Rodriguez-Commes Jose , Lopez Raquel , Rosales Oscar R. , Gasalla-Herraiz Jose , McCarthy Richard , Barrett Paula Q.
Published: December 2017

Acute parathyroid hormone exposure induces vascular smooth muscle relaxation. In contrast, continuous infusion of parathyroid hormone leads to vasoconstriction and an elevation of blood pressure. Despite the known effects of parathyroid hormone on vascular smooth muscle, possible direct effects on the vascular endothelium have not previously been investigated. Using a human umbilical vein endothelial cell line, we found that parathyroid hormone increased both intracellular calcium and cellular cAMP content in these endothelial cells. Furthermore, exposure of these cells to increasing concentrations of parathyroid hormone stimulated both [3H]thymidine incorporation and endothelin-1 secretion. Parathyroid hormone/parathyroid hormone-related peptide receptor mRNA could be detected at low levels in these cells. In summary, these data demonstrate that endothelium-derived cells contain functional parathyroid hormone receptors. The potential physiological role of these receptors remains to be determined.
Liver export protein synthetic rates are increased by oral meal feeding in weight-losing cancer patients
Authors: Barber Matthew D. , Fearon Kenneth C. H. , McMillan Donald C. , Slater Christine , Ross James A. , Preston Tom
Published: December 2017

We have demonstrated previously that, in the fasting state, whereas albumin synthesis is similar in cachectic cancer patients compared with controls, fibrinogen synthesis is increased. Whether synthesis of these proteins is altered after an oral meal was examined in eight weight-losing pancreatic cancer patients and six healthy controls by use of an intravenous flooding dose of [2H5]- or [2H8]phenylalanine. Cancer patients had a median weight loss of 19%, a significantly lower serum albumin concentration, and a significantly higher plasma fibrinogen concentration than controls ( P < 0.005). Fasting albumin synthesis rates were similar between cancer patients and controls (median total synthesis rate 11.3 vs. 13.9 g/day, respectively) and rose on feeding by a similar degree (median 29 and 24%). The fasting fibrinogen total synthetic rate was significantly higher in cancer patients than in controls (median 3.3 vs. 1.0 g/day, P = 0.0019). In cancer patients in the fed state, fibrinogen synthetic rate rose by a median of 38% ( P = 0.012), whereas in controls there was no significant change. These findings demonstrate significant upregulation by feeding of acute-phase protein synthesis in cachectic cancer patients.
4E-BP1 and S6K1: translational integration sites for nutritional and hormonal information in muscle
Authors: Shah O. Jameel , Anthony Joshua C. , Kimball Scot R. , Jefferson Leonard S.
Published: December 2017

Maintenance of cellular protein stores in skeletal muscle depends on a tightly regulated synthesis-degradation equilibrium that is conditionally modulated under an extensive range of physiological and pathophysiological circumstances. Recent studies have established the initiation phase of mRNA translation as a pivotal site of regulation for global rates of protein synthesis, as well as a site through which the synthesis of specific proteins is controlled. The protein synthetic pathway is exquisitely sensitive to the availability of hormones and nutrients and employs a comprehensive integrative strategy to interpret the information provided by hormonal and nutritional cues. The translational repressor, eukaryotic initiation factor 4E binding protein 1 (4E-BP1), and the 70-kDa ribosomal protein S6 kinase (S6K1) have emerged as important components of this strategy, and together they coordinate the behavior of both eukaryotic initiation factors and the ribosome. This review discusses the role of 4E-BP1 and S6K1 in translational control and outlines the mechanisms through which hormones and nutrients effect changes in mRNA translation through the influence of these translational effectors.
Insulin secretion and differential gene expression in glucose-responsive and -unresponsive MIN6 sublines
Authors: Minami Kohtaro , Yano Hideki , Miki Takashi , Nagashima Kazuaki , Wang Chang-Zheng , Tanaka Hiroko , Miyazaki Jun-Ichi , Seino Susumu
Published: December 2017

We have established two sublines derived from the insulin-secreting mouse pancreatic β-cell line MIN6, designated m9 and m14. m9 Cells exhibit glucose-induced insulin secretion in a concentration-dependent manner, whereas m14 cells respond poorly to glucose. In m14 cells, glucose consumption and lactate production are enhanced, and ATP production is largely through nonoxidative pathways. Moreover, lactate dehydrogenase activity is increased, and hexokinase replaces glucokinase as a glucose-phosphorylating enzyme. The ATP-sensitive K+channel activity and voltage-dependent calcium channel activity in m14 cells are reduced, and the resting membrane potential is significantly higher than in m9 cells. Thus, in contrast to m9, a model for β-cells with normal insulin response, m14 is a model for β-cells with impaired glucose-induced insulin secretion. By mRNA differential display of these sublines, we found 10 genes to be expressed at markedly different levels. These newly established MIN6 cell sublines should be useful tools in the analysis of the genetic and molecular basis of impaired glucose-induced insulin secretion.
Transcriptional regulation of gene expression in human skeletal muscle during recovery from exercise
Authors: Pilegaard Henriette , Ordway George A. , Saltin Bengt , Neufer P. Darrell
Published: December 2017

Exercise training elicits a number of adaptive changes in skeletal muscle that result in an improved metabolic efficiency. The molecular mechanisms mediating the cellular adaptations to exercise training in human skeletal muscle are unknown. To test the hypothesis that recovery from exercise is associated with transcriptional activation of specific genes, six untrained male subjects completed 60–90 min of exhaustive one-legged knee extensor exercise for five consecutive days. On day 5, nuclei were isolated from biopsies of the vastus lateralis muscle of the untrained and the trained leg before exercise and from the trained leg immediately after exercise and after 15 min, 1 h, 2 h, and 4 h of recovery. Transcriptional activity of the uncoupling protein 3 (UCP3), pyruvate dehydrogenase kinase 4 (PDK4), and heme oxygenase-1 (HO-1) genes (relative to β-actin) increased by three- to sevenfold in response to exercise, peaking after 1–2 h of recovery. Increases in mRNA levels followed changes in transcription, peaking between 2 and 4 h after exercise. Lipoprotein lipase and carnitine pamitoyltransferase I gene transcription and mRNA levels showed similar but less dramatic induction patterns, with increases ranging from two- to threefold. In a separate study, a single 4-h bout of cycling exercise ( n = 4) elicited from 5 to >20-fold increases in UCP3, PDK4, and HO-1 transcription, suggesting that activation of these genes may be related to the duration or intensity of exercise. These data demonstrate that exercise induces transient increases in transcription of metabolic genes in human skeletal muscle. Moreover, the findings suggest that the cumulative effects of transient increases in transcription during recovery from consecutive bouts of exercise may represent the underlying kinetic basis for the cellular adaptations associated with exercise training.
Glucose effects on lung surfactant kinetics in conscious pigs
Authors: Martini Wenjun Z. , Irtun Oivind , Chinkes David L. , Barrow Robert E. , Wolfe Robert R.
Published: December 2017

The primary goal of this study was to investigate the effects of glucose infusion on surfactant phosphatidylcholine (PC) metabolic kinetics in the lungs. A new stable isotope tracer model was used in which [1,2-13C2]acetate and uniformly labeled [U-13C16]palmitate were infused in 12 normal overnight-fasted pigs to quantify lung surfactant kinetics with or without glucose infusion (24 mg · kg−1· min−1). With glucose infusion, the rate of surfactant PC incorporation from de novo synthesized palmitate increased from the control value of 2.1 ± 0.2 to 15.5 ± 1.9 nmol PC-bound palmitate · h−1· g wet lung−1( P < 0.05), whereas the incorporation rate from plasma preformed palmitate decreased from the control value of 20.9 ± 1.9 to 11.6 ± 1.1 nmol palmitate · h−1· g wet lung−1( P < 0.05). The palmitate composition in lamellar body surfactant PC increased from the control value of 61.7 ± 2.1% to 75.9 ± 0.6% ( P < 0.05). The surfactant PC secretion rate decreased from the control value of 239.0 ± 26.1 to 81.9 ± 5.3 nmol PC-bound palmitate · h−1· g wet lung−1( P < 0.05). We conclude that, whereas surfactant secretion was inhibited by glucose infusion, neither total surfactant PC synthesis nor the surfactant PC pool size was significantly affected due to an increased reliance on de novo synthesized fatty acids.