bluuebunny/crossref_metadata_2025 huggingface dataset:
Leptin expression in adipose tissue from obese humans: depot-specific regulation by insulin and dexamethasone
Authors: Russell C. D. , Petersen R. N. , Rao S. P. , Ricci M. R. , Prasad A. , Zhang Y. , Brolin R. E. , Fried S. K.
Published: December 2017

We investigated the in vitro regulation of leptin expression in adipose tissue from severely obese women and men before and after culture with insulin (7 nM) and/or dexamethasone (25 nM). Leptin mRNA and leptin secretion were two- to threefold higher in subcutaneous vs. omental adipose tissue before culture. Dexamethasone transiently increased leptin mRNA approximately twofold in both depots after 1 day of culture [ P < 0.01 vs. basal (no hormone control)], but leptin secretion was only increased in omental adipose tissue ( P < 0.005 vs. basal). Insulin did not increase leptin mRNA in either depot but increased leptin secretion ∼1.5- to 3-fold in subcutaneous tissue throughout 7 days of culture ( P < 0.05 vs. basal). The combination of insulin and dexamethasone increased leptin mRNA and leptin secretion approximately two- to threefold in both depots at day 1( P < 0.005 vs. basal or insulin) and maintained leptin expression throughout 7 days of culture. We conclude that insulin and glucocorticoid have depot-specific effects and function synergistically as long-term regulators of leptin expression in omental and subcutaneous adipose tissue from obese subjects.
Hepatic and muscle glucose metabolism during total parenteral nutrition: impact of infection
Authors: McGuinness Owen P. , Donmoyer Christine , Ejiofor Joseph , McElligott Suzanne , Lacy D. Brooks
Published: December 2017

We examined the impact of infection on hepatic and muscle glucose metabolism in dogs adapted to chronic total parenteral nutrition (TPN). Studies were done in five conscious chronically catheterized dogs, in which sampling (artery, portal and hepatic vein, and iliac vein), infusion catheters (inferior vena cava), and Transonic flow probes (hepatic artery, portal vein, and iliac artery) were implanted. Fourteen days after surgery, dogs were placed on TPN. After 5 days of TPN, an infection was induced, and the TPN was continued. The balance of substrates across the liver and limb was assessed on the day before infection ( day 0) and 18 ( day 1) and 42 h ( day 2) after infection. On day 0, the liver was a marked net consumer of glucose (4.3 ± 0.6 mg ⋅ kg−1⋅ min−1) despite near normoglycemia (117 ± 5 mg/dl) and only mild hyperinsulinemia (16 ± 2 μU/ml). In addition, the majority (79 ± 13%) of the glucose taken up by the liver was released as lactate (34 ± 6 μmol ⋅ kg−1⋅ min−1). After infection, net hepatic glucose uptake decreased markedly on day 1(1.6 ± 0.9 mg ⋅ kg−1⋅ min−1) and remained suppressed on day 2 (2.4 ± 0.5 mg ⋅ kg−1⋅ min−1). Net hepatic lactate output also decreased on days 1 and 2 (15 ± 5 and 12 ± 3 μmol ⋅ kg−1⋅ min−1, respectively). This occurred despite increases in arterial plasma glucose on days 1 and 2 (135 ± 9 and 144 ± 9 mg/dl, respectively) and insulin levels on days 1 and 2 (57 ± 14 and 34 ± 9 μU/ml, respectively). In summary, the liver undergoes a profound adaptation to TPN, making it a major site of glucose disposal and conversion to lactate. Infection impairs hepatic glucose uptake, forcing TPN-derived glucose to be removed by peripheral tissues.
Counterregulatory hormones oscillate during steady-state hypoglycemia
Authors: Genter Pauline , Berman Nancy , Jacob Mary , Ipp Eli
Published: December 2017

During hypoglycemia, the magnitude of the counterregulatory response depends on the extent of plasma glucose reduction. However, our clinical observations during steady-state hypoglycemia indicate that symptom severity can change independently of plasma glucose concentrations, i.e., symptoms appeared to fluctuate despite stable glucose levels. This study was therefore designed to test the hypothesis that hormonal and symptomatic responses to hypoglycemia are pulsatile. Seven healthy subjects had serial blood sampling at 3-min intervals during 90 min of insulin-induced hypoglycemia. Mean ± SE plasma glucose levels plateaued at 62 ± 3 mg/dl. Counterregulatory hormones were significantly elevated ( P < 0.05–0.01, except norepinephrine) and strikingly pulsatile. Cluster analysis revealed pulses of large magnitude in plasma glucagon, epinephrine, and norepinephrine concentrations. Amplitudes were, respectively, 72 ± 4, 64 ± 8, and 48 ± 3% of the mean. Interpeak intervals were 27 ± 7, 19 ± 4, and 25 ± 5 min, respectively. Symptom score and cardiovascular responses were also pulsatile; their peaks were found to coincide with epinephrine peaks. We conclude that hormonal and symptomatic counterregulation in hypoglycemia, while critically driven by plasma glucose levels, is also influenced by an endogenous pulsatility that exists despite steady-state glucose concentrations.
Altered muscle metabolism associated with vasoconstriction in spontaneously hypertensive rats
Authors: Ye Ji-Ming , Colquhoun Eric Q.
Published: December 2017

In the rat muscle vascular bed, vasoconstrictors either increase or decrease oxygen consumption (V˙o 2). The present study compared the effects of norepinephrine (NE), angiotensin II (ANG II), and 5-hydroxytryptamine (5-HT) on vasoconstriction-associated metabolism in the constant-flow perfused hindlimb of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) in the absence of insulin. Basal perfusion pressure,V˙o 2, glucose uptake, and lactate production were increased by 21.4, 11.9, 46.4, and 44.9% ( P < 0.05 for all), respectively, in SHR, which also had higher blood pressure and metabolic rate ( P < 0.05) in vivo. Dose-response curves for NE-induced perfusion pressure,V˙o 2, and lactate production in SHR were shifted to the left compared with WKY. Associated with the increased perfusion pressure, NE-inducedV˙o 2 and glucose uptake were both decreased ( P < 0.01), particularly at high concentrations. These differences were unaffected by 10 μM propranolol but were all diminished by further addition of prazosin (2.5 nM). ANG II stimulatedV˙o 2, glucose uptake, and lactate production in both strains, but the increased lactate production was smaller in SHR ( P < 0.05) with a proportional decrease ( P< 0.05) in glucose uptake. Conversely, 5-HT decreasedV˙o 2 in both strains ( P < 0.01), and this effect was greater in SHR ( P < 0.01). These data suggest that SHR muscle thermogenesis and glucose uptake are impaired during vasoconstriction, especially in response to NE.
Pancreastatin inhibits insulin action in rat adipocytes
Authors: Sánchez-Margalet Víctor , González-Yanes Carmen
Published: December 2017

Pancreastatin (PST), a regulatory peptide with a general inhibitory effect on secretion, is derived from chromogranin A, a glycoprotein present throughout the neuroendocrine system. We have previously demonstrated the counterregulatory role of PST on insulin action in rat hepatocytes. Here, we are reporting the PST effects on rat adipocytes. PST dose dependently inhibits basal and insulin-stimulated glucose transport, lactate production, and lipogenesis, impairing the main metabolic actions of insulin in adipocytes. These effects were observed in a wide range of insulin concentrations, leading to a shift to the right in the dose-response curve. Maximal effect was observed at 10 nM PST, and the IC50value was ∼1 nM. Moreover, PST has a lipolytic effect in rat adipocytes (ED500.1 nM), although it was completely inhibited by insulin. In contrast, PST dose dependently stimulated protein synthesis and enhanced insulin-stimulated protein synthesis. In summary, these data show the lipokinetic effect of PST and the inhibitory effect of PST on insulin metabolic action within a range of physiological concentrations. Therefore, these results give new pathophysiological basis for the association of PST with insulin resistance.
Effect of rhIGF-I infusion on whole fetal and fetal skeletal muscle protein metabolism in sheep
Authors: Boyle David W. , Denne Scott C. , Moorehead Helen , Lee Wei-Hua , Bowsher Ronald R. , Liechty Edward A.
Published: December 2017

Insulin-like growth factor I (IGF-I) has been shown to have significant anabolic effects in the regulation of fetal protein metabolism. To investigate the tissue-specific effects of IGF-I on fetal skeletal muscle metabolism, we infused recombinant human (rh) IGF-I directly into the hindlimb of nine chronically catheterized, late-gestation fetal sheep. Substrate balance and amino acid kinetics were measured across the hindlimb and were compared with the effects at the whole body level before and during a 3-h infusion of rhIGF-I into the external iliac artery at 150 μg/h. Infusion of rhIGF-I resulted in increases in IGF-I concentrations by 2- to 5.75-fold in the ipsilateral iliac vein and by nearly 3-fold in the abdominal aorta. In the study limb, IGF-I had no effect on protein synthesis (phenylalanine rate of disposal 0.88 ± 0.13 before vs. 0.73 ± 0.19 μmol/min during IGF-I) or breakdown (phenylalanine rate of appearance 0.67 ± 0.13 before vs. 0.60 ± 0.17 μmol/min during IGF-I) and did not alter net phenylalanine balance. IGF-I also did not affect hindlimb oxygen or glucose uptake. In contrast, at the whole body level, the rate of appearance of leucine, indicative of fetal protein breakdown, decreased during IGF-I infusion (rate of appearance of leucine 41.1 ± 3.3 to 37.6 ± 2.7 μmol/min) as did fetal leucine oxidation (8.4 ± 0.8 to 6.8 ± 0.6 μmol/min). There was no change in the umbilical uptake of leucine, and although not statistically significant, fetal leucine accretion increased 2.4-fold. These results provide further evidence that IGF-I promotes fetal protein accretion; however, its site of action is in tissues other than skeletal muscle.
Endurance training changes in lipolytic responsiveness of obese adipose tissue
Authors: De Glisezinski I. , Crampes F. , Harant I. , Berlan M. , Hejnova J. , Langin D. , Rivière D. , Stich V.
Published: December 2017

The aim of this study was to investigate the effect of aerobic exercise training on the lipolytic response of adipose tissue in obese subjects. Thirteen men (body mass index = 36.9 ± 1.3 kg/m2) were submitted to aerobic physical training on a cycloergometer (30–45 min, 4 days a wk) for 3 mo. Adipocyte sensitivity to the action of catecholamines and insulin was studied in vitro before and after training. Training induced a decrease in the percentage of fat mass ( P < 0.05) without changing the body weight. Basal lipolysis and hormone-sensitive lipase activity were significantly decreased after training ( P < 0.05). The lipolytic effects of epinephrine, isoprenaline (β-adrenoceptor agonist), and dobutamine (β1-adrenoceptor agonist) were significantly increased ( P < 0.05) but not those of procaterol (β2-adrenoceptor agonist). The antilipolytic effects of α2-adrenoceptor and insulin were significantly decreased ( P < 0.05). Lipolysis stimulation by agents acting at the postreceptor level was unchanged after training. In conclusion, aerobic physical training in obese male subjects modifies adipose tissue lipolysis through an enhancement of β-adrenergic response and a concomitant blunting of adipocyte antilipolytic activity.
Human skeletal muscle pyruvate dehydrogenase kinase activity increases after a low-carbohydrate diet
Authors: Peters Sandra J. , St. Amand Timothy A. , Howlett Richard A. , Heigenhauser George J. F. , Spriet Lawrence L.
Published: December 2017

To characterize human skeletal muscle enzymatic adaptation to a low-carbohydrate, high-fat, and high-protein diet (LCD), subjects consumed a eucaloric diet consisting of 5% of the total energy intake from carbohydrate, 63% from fat, and 33% from protein for 6 days compared with their normal diet (52% carbohydrate, 33% fat, and 14% protein). Biopsies were taken from the vastus lateralis before and after 3 and 6 days on a LCD. Intact mitochondria were extracted from fresh muscle and analyzed for pyruvate dehydrogenase (PDH) kinase, total PDH, and carnitine palmitoyltransferase I activities and mitochondrial ATP production rate (using carbohydrate and fat substrates). β-Hydroxyacyl CoA dehydrogenase, active PDH (PDHa), and citrate synthase activities were also measured on whole muscle homogenates. PDH kinase (PDHK) was calculated as the absolute value of the apparent first-order rate constant of the inactivation of PDH in the presence of 0.3 mM Mg2+-ATP. PDHK increased dramatically from 0.10 ± 0.02 min−1to 0.35 ± 0.09 min−1at 3 days and 0.49 ± 0.06 min−1after 6 days. Resting PDHaactivity decreased from 0.63 ± 0.17 to 0.17 ± 0.04 mmol ⋅ min−1⋅ kg−1after 6 days on the diet, whereas total PDH activity did not change. Activities for all other enzymes were unaltered by the LCD. In summary, severe deficiency of dietary carbohydrate combined with a twofold increase in dietary fat and protein caused a rapid three- to fivefold increase in PDHK activity in human skeletal muscle. The increased PDHK activity downregulated the amount of PDH in its active form at rest and decreased carbohydrate metabolism. However, an increase in the activities of enzymes involved in fatty acid oxidation did not occur.
Hepatic glucose uptake rapidly decreases after removal of the portal signal in conscious dogs
Authors: Hsieh Po-Shiuan , Moore Mary Courtney , Neal Doss W. , Cherrington Alan D.
Published: December 2017

The aim of this study was to assess the decay of the effect of the portal signal on net hepatic glucose uptake (NHGU). Experiments were performed on five 42-h-fasted conscious dogs. After the 40-min basal period, somatostatin was given peripherally along with insulin (1.8 pmol ⋅ kg−1 ⋅ min−1) and glucagon (0.65 ng ⋅ kg−1 ⋅ min−1) intraportally. In the first experimental period (Pe-GLU-1; 90 min), glucose was infused into a peripheral vein to double the glucose load to the liver (HGL). In the second experimental period (Po-GLU; 90 min), glucose (20.1 μmol ⋅ kg−1 ⋅ min−1) was infused intraportally and the peripheral glucose infusion was reduced to maintain the same HGL. In the third period (Pe-GLU-2; 120 min), the portal glucose infusion was stopped and the peripheral glucose infusion was increased to again sustain HGL. Arterial insulin levels (42 ± 3, 47 ± 3, 43 ± 3 pmol/l) were basal and similar in the Pe-GLU-1, Po-GLU, and Pe-GLU-2 periods, respectively. Arterial glucagon levels were also basal and similar (51 ± 3, 49 ± 2, 46 ± 2 ng/l) in the three experimental periods. The glucose loads to the liver were 251 ± 11, 274 ± 14, and 276 ± 12 μmol ⋅ kg−1 ⋅ min−1, respectively. NHGU was 6.3 ± 2.4, 19.1 ± 2.8, and 9.2 ± 1.2 μmol ⋅ kg−1 ⋅ min−1, and nonhepatic glucose uptake (non-HGU) was 23.6 ± 3.0, 5.3 ± 1.8, and 25.5 ± 3.7 μmol ⋅ kg−1 ⋅ min−1in the three periods, respectively. Cessation of the portal signal for only 10 min shifted NHGU and non-HGU to 9.4 ± 2.2 and 25.0 ± 2.8 μmol ⋅ kg−1 ⋅ min−1, respectively; thus the effect of the portal signal was rapidly reversed both at the liver and peripheral tissues.
Erythrocyte glutathione deficiency in symptom-free HIV infection is associated with decreased synthesis rate
Authors: Jahoor Farook , Jackson Alan , Gazzard Brian , Philips Gary , Sharpstone Danny , Frazer Margaret E. , Heird William
Published: December 2017

Although several studies have documented intra- and extracellular glutathione (GSH) deficiency in asymptomatic human immunodeficiency virus (HIV) infection, the mechanisms responsible for the altered GSH homeostasis remain unknown. To determine whether decreased synthesis contributes to this alteration of GSH homeostasis, a primed-constant infusion of [2H2]glycine was used to measure the fractional and absolute rates of synthesis of GSH in five healthy and five symptom-free HIV-infected subjects before and after supplementation for 1 wk with N-acetylcysteine. The erythrocyte GSH concentration of the HIV-infected group was lower ( P < 0.01) than that of the control group (1.4 ± 0.16 vs. 2.4 ± 0.08 mmol/l). The smaller erythrocyte GSH pool of the HIV-infected group was associated with a significantly slower ( P < 0.01) absolute synthesis rate of GSH (1.15 ± 0.14 vs. 1.71 ± 0.15 mmol ⋅ l−1⋅ day−1) compared with controls. Cysteine supplementation elicited significant increases in both the absolute rate of synthesis and the concentration of erythrocyte GSH. These results suggest that the GSH deficiency of HIV infection is due in part to a reduced synthesis rate secondary to a shortage in cysteine availability.
Biological roles of angiotensin II via its type 2 receptor during rat follicle atresia
Authors: Kotani Eri , Sugimoto Masataka , Kamata Hachiroh , Fujii Nobuharu , Saitoh Masahiro , Usuki Satoshi , Kubo Takeshi , Song Keifu , Miyazaki Mizuo , Murakami Kazuo , Miyazaki Hitoshi
Published: December 2017

Type 1 angiotensin II (ANG II) receptors play crucial roles in the regulation of blood pressure and fluid osmolarity, whereas the physiological roles of type 2 ANG II receptors (AT2) remain unclear. Because AT2is expressed in atretic follicles where granulosa cells undergo apoptosis, we examined the space and time relationship between AT2expression and follicle atresia in vivo and the effect of AT2on follicle-stimulating hormone (FSH) actions in vitro. Binding studies, autoradiography, and RT-PCR of AT2revealed that the AT2content in granulosa cells was time dependently increased at both protein and mRNA levels in equine chorionic gonadotropin-treated immature female rats. This increase paralleled the progression of atresia. ANG II suppressed FSH-caused prevention of DNA fragmentation, increases in luteinizing hormone receptor content, and estrogen production through AT2in cultured granulosa cells. Moreover, FSH-induced stimulation of extracellular signal-regulated kinase activity, critical for cell survival, was inhibited by AT2stimulation. These results suggest that AT2mediates the progression of follicle atresia through granulosa cell apoptosis by inhibiting FSH actions.
Overexpression of hexokinase II increases insulinand exercise-stimulated muscle glucose uptake in vivo
Authors: Halseth Amy E. , Bracy Deanna P. , Wasserman David H.
Published: December 2017

The hypothesis of this investigation was that glucose uptake would be increased in skeletal muscle of transgenic mice (TG) overexpressing hexokinase II (HK II) compared with their nontransgenic littermates (NTG) during euglycemic hyperinsulinemia and treadmill exercise. For insulin experiments, catheters were surgically implanted in the jugular vein and carotid artery for infusions and sampling, respectively. Conscious mice underwent experiments ∼5 days later in which 4 mU ⋅ kg−1⋅ min−1insulin and variable glucose ( n = 7 TG and n = 7 NTG) or saline ( n = 5 TG and n = 4 NTG) was infused for 140 min. Over the last 40 min of the experiments, 2-deoxy-[3H]glucose ([2-3H]DG) was infused, after which muscles were removed. For the exercise experiments, jugular vein catheters were surgically implanted. Five days later, mice received a bolus of [2-3H]DG and then remained sedentary ( n = 6 TG and n = 8 NTG) or ran on a motorized treadmill ( n = 12 TG and n = 8 NTG) for 30 min. TG and NTG had similar muscle [2-3H]DG 6-phosphate ([2-3H]DGP) accumulation in the basal state ( P > 0.05). In the hyperinsulinemic experiments, TG required ∼25% more glucose to maintain euglycemia ( P < 0.05), and muscle [2-3H]DGP accumulation normalized to infusate [2-3H]DG was similarly increased ( P < 0.05). In the exercise experiments, muscle [2-3H]DGP accumulation was significantly greater in TG than NTG ( P < 0.05). In conclusion, we did not detect an effect of HK II overexpression on muscle [2-3H]DGP accumulation under basal conditions. Hyperinsulinemia and exercise shift the control of muscle glucose uptake so that phosphorylation is a more important determinant of the rate of this process.
Insulin regulation of renal glucose metabolism in humans
Authors: Cersosimo Eugenio , Garlick Peter , Ferretti John
Published: December 2017

Eighteen healthy subjects had arterialized hand and renal veins catheterized after an overnight fast. Systemic and renal glucose and glycerol kinetics were measured with [6,6-2H2]glucose and [2-13C]glycerol before and after 180-min peripheral infusions of insulin at 0.125 (LO) or 0.25 (HI) mU ⋅ kg−1⋅ min−1with variable [6,6-2H2]dextrose or saline (control). Renal plasma flow was determined by plasma p-aminohippurate clearance. Arterial insulin increased from 37 ± 8 to 53 ± 5 (LO) and to 102 ± 10 pM (HI, P < 0.01) but not in control (35 ± 8 pM). Arterial glucose did not change and averaged 5.2 ± 0.1 (control), 4.7 ± 0.2 (LO), and 5.1 ± 0.2 (HI) μmol/ml; renal vein glucose decreased from 4.8 ± 0.2 to 4.5 ± 0.2 μmol/ml (LO) and from 5.3 ± 0.2 to 4.9 ± 0.1 μmol/ml (HI) with insulin but not saline infusion (5.3 ± 0.1 μmol/ml). Endogenous glucose production decreased from 9.9 ± 0.7 to 6.9 ± 0.5 (LO) and to 5.7 ± 0.5 (HI) μmol ⋅ kg−1⋅ min−1; renal glucose production decreased from 2.5 ± 0.6 to 1.5 ± 0.5 (LO) and to 1.2 ± 0.6 (HI) μmol ⋅ kg−1⋅ min−1, whereas renal glucose utilization increased from 1.5 ± 0.6 to 2.6 ± 0.7 (LO) and to 2.9 ± 0.7 (HI) μmol ⋅ kg−1⋅ min−1after insulin infusion (all P < 0.05 vs. baseline). Neither endogenous glucose production (10.0 ± 0.4), renal glucose production (1.1 ± 0.4), nor renal glucose utilization (0.8 ± 0.4) changed in the control group. During insulin infusion, systemic gluconeogenesis from glycerol decreased from 0.67 ± 0.05 to 0.18 ± 0.02 (LO) and from 0.60 ± 0.04 to 0.20 ± 0.02 (HI) μmol ⋅ kg−1⋅ min−1( P < 0.01), and renal gluconeogenesis from glycerol decreased from 0.10 ± 0.02 to 0.02 ± 0.02 (LO) and from 0.15 ± 0.03 to 0.09 ± 0.03 (HI) μmol ⋅ kg−1⋅ min−1( P < 0.05). In contrast, during saline infusion, systemic (0.66 ± 0.03 vs. 0.82 ± 0.05 μmol ⋅ kg−1⋅ min−1) and renal gluconeogenesis from glycerol (0.11 ± 0.02 vs. 0.41 ± 0.04 μmol ⋅ kg−1⋅ min−1) increased ( P < 0.05 vs. baseline). We conclude that glucose production and utilization by the kidney are important insulin-responsive components of glucose metabolism in humans.
Plasma insulin rise precedes rise inob mRNA expression and plasma leptin in gold thioglucose-obese mice
Authors: Bryson Janet M. , Phuyal Jenny L. , Proctor Deborah R. , Blair Stephen C. , Caterson Ian D. , Cooney Gregory J.
Published: December 2017

Circulating leptin levels are strongly related to the degree of adiposity, with hyperleptinemia being associated with hyperinsulinemia. In the gold thioglucose-injected mouse (GTG), hyperinsulinemia is an early abnormality in the development of insulin resistance and obesity. In this study, hyperinsulinemia occurred 1 wk post-GTG [GTG, 199 ± 43; age-matched controls (CON), 53 ± 5 μU/ml; P < 0.001], with leptin levels not rising until 2 wk post-GTG (CON, 3.2 ± 0.3; GTG, 9.9 ± 1.7 ng/ml; P < 0.001) in parallel with increases in the size of different fat pads and increased expression of ob mRNA. The ratio of serum leptin to fat pad weight was significantly higher in GTG mice 12 wk postinjection. Starvation-induced reductions in serum leptin (50%), glucose (50%), and insulin (74%) were greater than decreases in fat pad weight (18%). Adrenalectomy decreased both adiposity and serum leptin within 1 wk in both CON and GTG and altered the serum leptin level-to-fat pad weight ratio in CON. Thus hyperinsulinemia preceded increased ob expression and hyperleptinemia, which occurred in parallel with increasing adiposity, consistent with the role of leptin as an indicator of energy supplies. Changes in hormonal and nutritional status may modify this relationship.
The importance of pyruvate availability to PDC activation and anaplerosis in human skeletal muscle
Authors: Constantin-Teodosiu Dumitru , Simpson Elizabeth J. , Greenhaff Paul L.
Published: December 2017

No studies have singularly investigated the relationship between pyruvate availability, pyruvate dehydrogenase complex (PDC) activation, and anaplerosis in skeletal muscle. This is surprising given the functional importance attributed to these processes in normal and disease states. We investigated the effects of changing pyruvate availability with dichloroacetate (DCA), epinephrine, and pyruvate infusions on PDC activation and accumulation of acetyl groups and tricarboxylic acid (TCA) cycle intermediates (TCAI) in human muscle. DCA increased resting PDC activity sixfold ( P < 0.05) but decreased the muscle TCAI pool (mmol/kg dry muscle) from 1.174 ± 0.042 to 0.747 ± 0.055 ( P < 0.05). This was probably a result of pyruvate being diverted to acetyl-CoA and acetylcarnitine after near-maximal activation of PDC by DCA. Conversely, neither epinephrine nor pyruvate activated PDC. However, both increased the TCAI pool (1.128 ± 0.076 to 1.614 ± 0.188, P < 0.05 and 1.098 ± 0.059 to 1.385 ± 0.114, P < 0.05, respectively) by providing a readily available pool of pyruvate for anaplerosis. These data support the hypothesis that TCAI pool expansion is principally a reflection of increased muscle pyruvate availability and, together with our previous work (J. A. Timmons, S. M. Poucher, D. Constantin-Teodosiu, V. Worrall, I. A. Macdonald, and P. L. Greenhaff. J. Clin. Invest. 97: 879–883, 1996), indicate that TCA cycle expansion may be of little functional significance to TCA cycle flux. It would appear therefore that the primary effect of DCA on oxidative ATP provision is to provide a readily available pool of acetyl groups to the TCA cycle at the onset of exercise rather than increasing TCA cycle flux by expanding the TCAI pool.
Nonsaturable entry of neuropeptide Y into brain
Authors: Kastin Abba J. , Akerstrom Victoria
Published: December 2017

Neuropeptide Y (NPY) is found and is active both in the periphery and brain, but its crossing of the blood-brain barrier (BBB) in either direction has not been measured. We used multiple time-regression analysis to determine that radioactively labeled NPY injected intravenously entered the brain much faster than albumin, with an influx constant of 2.0 × 10−4ml ⋅ g ⋅ −1 ⋅ min−1. However, this rate of entry was not significantly changed by injection of 10 μg/mouse of excess NPY, by leptin, or by food deprivation. HPLC showed that most of the NPY entering the brain was intact, and capillary depletion with and without washout showed that the NPY did not remain bound to endothelial cells or associated with vascular elements. Perfusion in a blood-free solution eliminated binding to serum proteins as an explanation for the lack of saturation. Efflux of labeled NPY from the brain occurred at the same rate as albumin, reflecting the normal rate of reabsorption of cerebrospinal fluid. Thus NPY can readily enter the brain from blood by diffusion across the BBB.
Effect of fast duration on disposition of an intraduodenal glucose load in the conscious dog
Authors: Galassetti Pietro , Hamilton Katherine S. , Gibbons Fiona K. , Bracy Deanna P. , Lacy Drury B. , Cherrington Alan D. , Wasserman David H.
Published: December 2017

The effects of prior fast duration (18 h, n = 8; 42 h, n = 8) on the glycemic and tissue-specific responses to an intraduodenal glucose load were studied in chronically catheterized conscious dogs. [3-3H]glucose was infused throughout the study. After basal measurements, glucose spiked with [U-14C]glucose was infused for 150 min intraduodenally. Arterial insulin and glucagon were similar in the two groups. Arterial glucose (mg/dl) rose ∼70% more during glucose infusion after 42 h than after an 18-h fast. The net hepatic glucose balance (mg ⋅ kg−1⋅ min−1) was similar in the two groups (basal: 1.8 ± 0.2 and 2.0 ± 0.3; glucose infusion: −2.2 ± 0.5 and −2.2 ± 0.7). The intrahepatic fate of glucose was 79% glycogen, 13% oxidized, and 8% lactate release after a 42-h fast; it was 23% glycogen, 21% oxidized, and 56% lactate release after an 18-h fast. Net hindlimb glucose uptake was similar between groups. The appearance of intraduodenal glucose during glucose infusion (mg/kg) was 900 ± 50 and 1,120 ± 40 after 18- and 42-h fasts ( P < 0.01). Conclusion: glucose administration after prolonged fasting induces higher circulating glucose than a shorter fast (increased appearance of intraduodenal glucose); liver and hindlimb glucose uptakes and the hormonal response, however, are unchanged; finally, an intrahepatic redistribution of carbons favors glycogen deposition.
Comparison of the LDL-receptor binding of VLDL and LDL from apoE4 and apoE3 homozygotes
Authors: Mamotte Cyril D. S. , Sturm Marian , Foo Jock I. , van Bockxmeer Frank M. , Taylor Roger R.
Published: December 2017

Compared with apolipoprotein E3 (apoE3), apoE2 is less effective in mediating the binding of lipoproteins to the low-density lipoprotein (LDL) receptor. The influence of the E4 isoform, which is associated with adverse effects on plasma lipids and coronary heart disease, is less clear. We compared the ability of very low density lipoprotein (VLDL) and LDL from paired E4/4 and E3/3 subjects to compete against125I-labeled LDL for binding with the LDL receptor on cultured fibroblasts and Hep G2 cells. The concentrations of VLDL or LDL required to inhibit binding of125I-LDL by 50% (IC50, μg apoB/ml) were determined, and results were assessed in terms of an IC50ratio, E4/4 IC50relative to E3/3 IC50, to reduce the influence of interassay variability. In Hep G2 cells, E4/4 VLDL was more effective than E3/3 VLDL in competing for the LDL receptor, the IC50ratio being lower than unity (0.73 ± 0.31, P < 0.05, two-tailed t-test). IC50values themselves were marginally lower in E4/4 than E3/3 subjects (3.7 ± 1.3 vs. 6.1 ± 3.7, P < 0.08). However, there was no difference between E4/4 and E3/3 VLDL in competing for the LDL receptor on fibroblasts or between E4/4 and E3/3 LDL in competing for the LDL receptor on either cell type. These results suggest that inheritance of apoE4 is associated with an increased affinity of VLDL particles for LDL receptors on hepatocytes and may partly explain the influence of the E4 isoform on lipid metabolism.
Clearance of IGFs and insulin from wounds: effect of IGF-binding protein interactions
Authors: Robertson J. Gray , Belford David A. , Ballard F. John
Published: December 2017

We have examined the role binding proteins have in regulating the clearance of exogenous growth factors from wounds. Hunt-Schilling chambers were subcutaneously implanted in rats, and the clearance of insulin-like growth factor (IGF) I from the chamber wound fluid was compared with IGF-II, LR3-IGF-I, which binds poorly to IGF-binding proteins (IGFBP), or insulin. Elimination rate constants of the slow phase of the decay curves did not differ between IGF-I and IGF-II. However, LR3-IGF-I and insulin were cleared more rapidly from wound fluid than IGF-I so that the half-lives for IGF-I, IGF-II, LR3-IGF-I, and insulin were 872, 861, 563, and 324 min, respectively. In wound fluid, minimal degradation of the IGFs occurred, whereas insulin was degraded considerably. The increased clearance of LR3-IGF-I and insulin equated with a reduced association with wound fluid IGFBPs, and increased amounts of radioactivity of these peptides were detected in the circulation and urine. These results show that this model of wound repair may be of use in examining the kinetics of growth factors and other bioactive molecules in extravascular spaces and support the hypothesis that IGFBPs can be significant regulators of IGF bioavailability in vivo.
Antioxidants reversibly inhibit the spontaneous resumption of meiosis
Authors: Takami M. , Preston S. L. , Toyloy V. A. , Behrman Harold R.
Published: December 2017

We previously showed that the cell-permeant antioxidant 2(3)- tert-butyl-4-hydroxyanisole (BHA) inhibited germinal vesicle breakdown (GVBD) in oocyte-cumulus complexes (OCC) of the rat. The objective of the present studies was to assess other antioxidants and whether such inhibition was reversible. Spontaneous GVBD in OCC incubated for 2 h was significantly inhibited ( P < 0.005) by nordihydroguaiaretic acid (NDGA; GVBD = 19.4%), BHA (GVBD = 25.7%), octyl gallate (OG; GVBD = 52.2%), ethoxyquin (EQ; GVBD = 58.8%), 2,6-di- tert-butyl-hydroxymethyl phenol (TBHMP; GVBD = 59%), butylated hydroxytoluene (BHT; GVBD = 59.5%), and tert-butyl hydroperoxide (TBHP; GVBD = 60.0%). Other antioxidants that produced lower but significant ( P < 0.05) inhibition of oocyte maturation included propyl gallate (PG; GVBD = 70.3%), 2,4,5-trihydroxybutrophenone (THBP; GVBD = 71.4%), and lauryl gallate (LG; GVBD = 71.4%). Antioxidants that had no effect on oocyte maturation at the same concentration (100 μM) included ascorbic acid, vitamin E, and Trolox. Inhibition of GVBD was evident for up to 8 h of incubation of OCC and denuded oocytes (DO) with BHA or NDGA and was reversed by washing. NDGA was less potent than BHA for inhibition of GVBD in DO, unlike that seen with OCC. Oocyte maturation was induced by incubation of follicles for 3 h with human chorionic gonadotropin (hCG), and this response was inhibited by BHA or NDGA. These findings support the conclusion that cell-permeant antioxidants inhibit spontaneous resumption of meiosis, which may implicate a role of oxygen radicals in oocyte maturation.
Regulation of protein synthesis after acute resistance exercise in diabetic rats
Authors: Farrell Peter A. , Fedele Mark J. , Vary Thomas C. , Kimball Scot R. , Lang Charles H. , Jefferson Leonard S.
Published: December 2017

These studies determined whether insulin-like growth factor-I (IGF-I) involvement in exercise-stimulated anabolic processes becomes more evident during hypoinsulinemia. Male Sprague-Dawley rats ( n = 6–12/group) were made diabetic (blood glucose ≅ 300 mg/dl) by partial pancreatectomy (PPX) or remained nondiabetic (glucose ≅ 144 mg/dl). Rats performed acute resistance exercise by repetitive standing on the hindlimbs with weighted backpacks (ex), or they remained sedentary (sed). Resistance exercise caused increases in rates of protein synthesis (nmol Phe incorporated ⋅ g muscle−1⋅ h−1, measured for gastrocnemius muscle in vivo 16 h after exercise) for both nondiabetic [sed = 154 ± 6 (SE) vs. ex = 189 ± 7] and diabetic rats (PPXsed = 152 ± 11 vs. PPXex = 202 ± 14, P < 0.05). Arterial plasma insulin concentrations in diabetic rats, ≅180 pM, were less than one-half those found in nondiabetic rats, ≅444 pM, ( P < 0.05). The activity of eukaryotic initiation factor 2B (eIF2B; pmol GDP exchanged/min) was higher ( P < 0.05) in ex rats (sed = 0.028 ± 0.006 vs. ex = 0.053 ± 0.015; PPXsed = 0.033 ± 0.013 vs. PPXex = 0.047 ± 0.009) regardless of diabetic status. Plasma IGF-I concentrations were higher in ex compared with sed diabetic rats ( P < 0.05). In contrast, plasma IGF-I was not different in nondiabetic ex or sed rats. Muscle IGF-I (ng/g wet wt) was similar in ex and sed nondiabetic rats, but in diabetic rats was 2- to 3-fold higher in ex ( P < 0.05) than in sed rats. In conclusion, moderate hypoinsulinemia that is sufficient to alter glucose homeostasis does not inhibit an increase in rates of protein synthesis after acute moderate-intensity resistance exercise. This preserved response may be due to a compensatory increase in muscle IGF-I content and a maintained ability to activate eIF2B.
Thyroid hormones modulate zinc transport activity of rat intestinal and renal brush-border membrane
Authors: Prasad Rajendra , Kumar Vivek , Kumar Rajinder , Singh Kiran Pal
Published: December 2017

Thyroid hormone status influences the Zn2+and metallothionein levels in intestine, liver, and kidney. To evaluate the impact of thyroid hormones on Zn2+metabolism, Zn2+uptake studies were carried out in intestinal and renal brush-border membrane vesicles (BBMV). Steady-state Zn2+transport in intestinal and renal cortical BBMV was increased in hyperthyroid (Hyper-T) rats and decreased in the hypothyroid (Hypo-T) rats relative to euthyroid (Eu-T) rats. In both the intestinal and renal BBMV, Hyper-T rats showed a significant increase in maximal velocity compared with Eu-T and Hypo-T rats. Apparent Michaelis constant was unaltered in intestinal and renal BBMV prepared from the three groups. Fluorescence anisotropy of diphenyl hexatriene was decreased significantly in intestinal and renal brush-border membrane (BBM) isolated from Hyper-T rats compared with Hypo-T and Eu-T rats. A significant reduction in the microviscosity and transition temperature for Zn2+uptake in intestinal and renal BBM from Hyper-T rats is in accordance with the increased fluidity of these BBMs. These findings suggest that the increased rate of Zn2+transport in response to thyroid hormone status could be associated with either an increase in the number of Zn2+transporters or an increase in the active transporters due to alteration in the membrane fluidity. Thus the thyroid hormone-mediated change in membrane fluidity might play an important role in modulating Zn2+transport activity of intestinal and renal BBM.
Regional specificity of ASP binding in human adipose tissue
Authors: Saleh Jumana , Christou Nick , Cianflone Katherine
Published: December 2017

Obesity, in particular omental (OM) adiposity, is associated with diabetes and cardiovascular disease. Thus site-specific regulation of fat storage is important to understand. Acylation-stimulating protein (ASP) is a potent stimulator of glucose transport and triglyceride synthesis in adipocytes. In the present study, we characterized receptor binding of125I-labeled ASP to human adipocyte plasma membranes from paired OM and subcutaneous (SC) sites in normal (N) and obese (O) male (M) and female (F) subjects ( n = 24). Overall, specific binding of125I-ASP was in the order of SC > OM and O > N (in SC tissue, particularly in F). Receptor affinity of125I-ASP was higher [lower dissociation constant ( Kd)] in SC than in OM (63.6 ± 16.2 vs. 160.7 ± 38.6 nM, P < 0.02), especially in F (37.0 ± 11.1 F-N and 26.3 ± 6.7 nM F-O) and lower (higher Kd) in male OM (291.8 ± 116.8 M-N and 149.4 ± 56.4 M-O). The greater binding and higher affinity of125I-ASP binding to SC suggests that ASP may be an important factor in maintaining regional adipose tissue mass. Conversely, lower binding and receptor affinity in male OM adipose tissue may contribute to the fatty acid imbalance and metabolic complications associated with this syndrome, by reducing the efficiency of adipose fatty acid trapping by the ASP pathway.
Regional glycerol and free fatty acid metabolism before and after meal ingestion
Authors: Jensen Michael D.
Published: December 2017

We measured splanchnic and leg glycerol [and free fatty acid (FFA)] uptake and release in 11 healthy volunteers before and after meal ingestion to assess whether regional FFA-to-glycerol release ratios mirror systemic release ratios. Basal splanchnic triglyceride release was also assessed. Although basal splanchnic glycerol uptake (111 ± 18 μmol/min) accounted for most of systemic glycerol rate of appearance (156 ± 20 μmol/min), leg glycerol uptake was also noted. The basal, systemic FFA-to-glycerol release ratio was less (2.6 ± 0.2, P < 0.05) than the splanchnic ratio of 6.1 ± 1.3, and the leg FFA-to-glycerol release ratio under fed conditions was less than the systemic ratio (0.9 ± 0.1 vs. 1.6 ± 0.2, respectively, P< 0.05). Basal splanchnic triglyceride production rates were 74 ± 20 μmol/min, which could produce equimolar amounts of glycerol in the peripheral circulation via lipoprotein lipase action. In summary, 1) regional FFA-to-glycerol release ratios do not mirror systemic ratios, 2) leg glycerol uptake occurs in humans, and 3) splanchnic triglyceride production rates are substantial relative to systemic glycerol appearance. Glycerol appearance rates may not be a quantitative index of whole body lipolysis.
Regulation of GLUT-3 glucose transporter in the hippocampus of diabetic rats subjected to stress
Authors: Reagan Lawrence P. , Magariños Ana Maria , Lucas Louis R. , van Bueren Antonia , McCall Anthony L. , McEwen Bruce S.
Published: December 2017

Previous studies from our laboratory have demonstrated that chronic stress produces molecular, morphological, and ultrastructural changes in the rat hippocampus that are accompanied by cognitive deficits. Glucocorticoid attenuation of glucose utilization is proposed to be one of the causative factors involved in stress-induced changes in the hippocampus, producing an energy-compromised environment that may make hippocampal neuronal populations more vulnerable to neurotoxic insults. Similarly, diabetes potentiates neuronal damage in acute neurotoxic events, such as ischemia and stroke. Accordingly, the current study examined the regulation of the neuron-specific glucose transporter, GLUT-3, in the hippocampus of streptozotocin-induced diabetic rats subjected to restraint stress. Diabetes leads to significant increases in GLUT-3 mRNA and protein expression in the hippocampus, increases that are not affected by stress. Collectively, these results suggest that streptozotocin-induced increases in GLUT-3 mRNA and protein expression in the hippocampus may represent a compensatory mechanism to increase glucose utilization during diabetes and also suggest that modulation of GLUT-3 expression is not responsible for glucocorticoid impairment of glucose utilization.
Mechanism of the upregulation of erythropoietin-induced uptake clearance by the spleen
Authors: Kato Motohiro , Kato Yukio , Sugiyama Yuichi
Published: December 2017

Repeated administration of recombinant human erythropoietin (rhEPO) causes upregulation of receptor-mediated tissue uptake by the spleen (Kato, M., H. Kamiyama, A. Okazaki, K. Kumaki, Y. Kato, and Y. Sugiyama. J. Pharmacol. Exp. Ther. 283: 520–527, 1997). To discover whether such upregulation is due to an increase in target cells, the numbers of colony-forming unit erythroids (CFU-E) and burst-forming unit erythroids (BFU-E), the precursor of CFU-E, were measured in the spleen after rhEPO treatment. The uptake clearance of125I-labeled rhEPO by the spleen was almost proportional to the number of CFU-E, suggesting that the upregulation is due to an increased number of CFU-E. When growth cells were metabolically labeled with [3H]thymidine in vivo, the radioactivity in bone marrow fell significantly after rhEPO treatment, whereas that in the spleen increased significantly. A cell-fractionation study using Percoll revealed that the radioactivity in the BFU-E fraction of splenic cells increased initially after rhEPO treatment, followed by an increase in radioactivity in the CFU-E fraction with a concomitant reduction in radioactivity in the BFU-E fraction. These results demonstrate that EPO stimulates the migration of BFU-E from bone marrow to spleen, followed by its differentiation into CFU-E in the spleen. In conclusion, the upregulation observed in the spleen is due to its stimulatory effect on the migration of BFU-E.
Protein kinetics during and after long-duration spaceflight on MIR
Authors: Stein T. P. , Leskiw M. J. , Schluter M. D. , Donaldson M. R. , Larina I.
Published: December 2017

Human spaceflight is associated with a loss of body protein. Bed rest studies suggest that the reduction in the whole body protein synthesis (PS) rate should be ∼15%. The objectives of this experiment were to test two hypotheses on astronauts and cosmonauts during long-duration (>3 mo) flights on MIR: that 1) the whole body PS rate will be reduced and 2) dietary intake and the PS rate should be increased postflight because protein accretion is occurring. The15N glycine method was used for measuring whole body PS rate before, during, and after long-duration spaceflight on the Russian space station MIR. Dietary intake was measured together with the protein kinetics. Results show that subjects lost weight during flight (4.64 ± 1.0 kg, P < 0.05). Energy intake was decreased inflight (2,854 ± 268 vs. 2,145 ± 190 kcal/day, n = 6, P < 0.05), as was the PS rate (226 ± 24 vs. 97 ± 11 g protein/day, n = 6, P < 0.01). The reduction in PS correlated with the reduction in energy intake ( r 2 = 0.86, P < 0.01, n = 6). Postflight energy intake and PS returned to, but were not increased over, the preflight levels. We conclude that the reduction in PS found was greater than predicted from ground-based bed rest experiments because of the shortfall in dietary intake. The expected postflight anabolic state with increases in dietary intake and PS did not occur during the first 2 wk after landing.
A marathon run increases the susceptibility of LDL to oxidation in vitro and modifies plasma antioxidants
Authors: Liu Ming-Lin , Bergholm Robert , Mäkimattila Sari , Lahdenperä Sanni , Valkonen Miia , Hilden Hannele , Yki-Järvinen Hannele , Taskinen Marja-Riitta
Published: December 2017

Physical activity increases the production of oxygen free radicals, which may consume antioxidants and oxidize low-density lipoprotein (LDL). To determine whether this occurs during strenuous aerobic exercise, we studied 11 well-trained runners who participated in the Helsinki City Marathon. Blood samples were collected before, immediately after, and 4 days after the race to determine its effect on circulating antioxidants and LDL oxidizability in vitro. LDL oxidizability was increased as determined from a reduction in the lag time for formation of conjugated dienes both immediately after (180 ± 7 vs. 152 ± 4 min, P < 0.001) and 4 days after (155 ± 7 min, P < 0.001) the race. No significant changes in lipid-soluble antioxidants in LDL or in the peak LDL particle size were observed after the race. Total peroxyl radical trapping antioxidant capacity of plasma (TRAP) and uric acid concentrations were increased after the race, but, except for TRAP, these changes disappeared within 4 days. Plasma thiol concentrations were reduced after the race. No significant changes were observed in plasma ascorbic acid, α-tocopherol, β-carotene, and retinol concentrations after the marathon race. We conclude that strenuous aerobic exercise increases the susceptibility of LDL to oxidation in vitro for up to 4 days. Although the increase in the concentration of plasma TRAP reflects an increase of plasma antioxidant capacity, it seems insufficient to prevent the increased susceptibility of LDL to oxidation in vitro, which was still observed 4 days after the race.
Passage of leptin across the blood-testis barrier
Authors: Banks William A. , McLay Robert N. , Kastin Abba J. , Sarmiento Ulla , Scully Sheila
Published: December 2017

Leptin is a 17-kDa protein, secreted by fat, that controls adiposity and has been proposed to have numerous effects on reproduction in the mouse. To assess whether the effects of leptin on testicular function are direct, we determined whether leptin can cross the murine blood-testis barrier. Multiple time regression analysis showed that a small amount of blood-borne leptin is able to enter the testis but does so by a nonsaturable process. In addition, no significant expression of leptin receptors was found at the Leydig cells or Sertoli cells of the testis. This compares with the presence of a saturable transport system for leptin at the blood-brain barrier and abundant receptors for leptin at the leptomeninges, neurons, and choroid plexus of the central nervous system (CNS). These results support the hypothesis that the effects of leptin on reproductive function are not mediated at the level of the testis but indirectly, probably through the CNS.