bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of hepatic Ra UDP-glucose in vivo in rats: relation to glycogen deposition and labeling patterns
Authors: Hellerstein M. K. , Letscher A. , Schwarz J. M. , Cesar D. , Shackleton C. H. , Turner S. , Neese R. , Wu K. , Bock S. , Kaempfer S.
Published: December 2017

We previously described an isotopic method for quantifying the rate of appearance of hepatic UDP-glucose (Ra UDP-Glc) and the direct entry of glucose into hepatic UDP-Glc in humans. Here, the method is tested in depth in rats. The basic principles are that dilution of labeled galactose in hepatic UDP-Glc, sampled noninvasively by the xenobiotic glucuronate (GlcUA) method, reveals Ra UDP-Glc. First, labeling patterns in secreted acetaminophen-GlcUA were compared with hepatic glycogen and plasma glucose by use of mass isotopomer distribution analysis from [2-(13)C]glycerol. Labeling was consistent with common precursor pools of glucose 6-phosphate and triose-phosphate for all end products studied in fasted and in intravenous glucose- and fructose-infused states. Next, [1-(3)H]galactose was administered. After a 24-h fast, Ra UDP-Glc was 25.0 +/- 1.7 mumol.kg body wt-1.min-1 and rose to 57.7 and 72.7 mumol.kg-1.min-1 at intravenous glucose infusion rates of 111 and 167-194 mumol.kg-1.min-1, respectively. Liver glycogen deposition correlated closely with Ra UDP-Glc (R2 = 0.76), although the turnover value was approximately 50% higher than the net deposition rate. In conclusion, the turnover of an intrahepatic metabolite, UDP-Glc, can be measured noninvasively, and Ra UDP-Glc correlates with liver glycogen deposition in rats.
Hormone-specific alterations of T4, T3, and reverse T3 metabolism with recent ethanol abstinence in humans
Authors: Kaptein E. M.
Published: December 2017

Effects of recent alcoholic withdrawal on thyroxine (T4), 3,5,3'-triiodothyronine (T3), and reverse T3 (rT3) metabolism were determined by serum tracer kinetic studies in recently abstinent alcoholics without overt hepatocellular injury or caloric deprivation. Data were compared with those of normal subjects using a three-pool model, with rapidly and slowly equilibrating pools exchanging with serum. Significant differences included 1) reduced serum total rT3 levels (to 69% of normal) and rT3 degradation rates (to 61%); 2) increased rT3 binding in rapidly (to 557%) but reduced binding in slowly (to 13%) equilibrating tissues, with opposite effects on rT3 fractional transfer rates to serum from rapidly (to 7.5%) and slowly equilibrating sites (to 669%); 3) increased T4 fractional transfer rates from serum to rapidly equilibrating tissues (to 122%); and 4) increased T4 binding to both rapidly (to 195%) and slowly (to 190%) equilibrating tissues. T3 kinetics were not significantly altered. Thus recently abstinent alcoholics have hormone-specific alterations of T4, T3, and rT3 transfer, distribution, and metabolism distinct from other nonthyroidal illnesses or caloric deprivation. Furthermore, these data indicate separate transfer processes for T4, T3, and rT3 from serum to tissue sites and hormone-specific tissue binding characteristics in humans in vivo.
Prostaglandin F2alpha stimulates interleukin-6 synthesis via activation of PKC in osteoblast-like cells
Authors: Kozawa O. , Suzuki A. , Tokuda H. , Uematsu T.
Published: December 2017

In previous studies, we reported that prostaglandin F2alpha (PGF2alpha) stimulates phosphoinositide hydrolysis by phospholipase C and phosphatidylcholine hydrolysis by phospholipase D in osteoblast-like MC3T3-E1 cells. In the present study, we examined the effect of PGF2alpha on synthesis of interleukin-6 (IL-6) and the involvement of protein kinase C (PKC) activation in the IL-6 synthesis in these cells. PGF2alpha significantly stimulated IL-6 synthesis in a dose-dependent manner in the range between 10 nM and 10 microM. A PKC-activating phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), induced IL-6 synthesis. On the contrary, 4alpha-phorbol 12,13-didecanoate, a PKC-nonactivating phorbol ester, had no effect. The synthesis of IL-6 stimulated by a combination of PGF2alpha and TPA was not additive. Staurosporine, an inhibitor for protein kinases that suppressed the TPA-induced IL-6 synthesis, significantly inhibited the PGF2alpha-induced IL-6 synthesis. Calphostin C, a highly specific PKC inhibitor, also suppressed the PGF2alpha-stimulated synthesis of IL-6. The effect of PGF2alpha on IL-6 synthesis in PKC-downregulated cells was much weaker than that in intact cells. These results strongly suggest that PGF2alpha induces IL-6 synthesis via PKC activation in osteoblast-like cells.
Acute modulation of active carrier-mediated brain-to-blood transport of corticotropin-releasing hormone
Authors: Martins J. M. , Banks W. A. , Kastin A. J.
Published: December 2017

The unidirectional brain-to-blood transport system for corticotropin-releasing hormone (CRH) across the blood-brain barrier could be instrumental in the homeostasis of central CRH. To characterize this system, the intracerebroventricular injection of 125I-CRH was used in mice. CRH was rapidly transported out of the brain with a half-time disappearance (t1/2) of 15 min, much faster than albumin (t1/2 = 50 min). Kinetic analysis revealed a saturable component with a low maximum velocity (apaproximately 0.020 nmol x min(-1) x brain(-1)) and low capacity (Michaelis constant approximately 1.4 nmol/brain). Transport was inhibited by verapamil, ouabain, and colchicine but not by cyclosporin. Transport was increased by corticosterone and inhibited by tumor necrosis factor-alpha and beta-endorphin. These results suggest that the specific unidirectional brain-to-blood transport system for CRH is dependent on energy and calcium channels, involves microtubules, is independent of the P-glycoprotein transporter, and is acutely modulated by adrenal steroids, cytokines, and endogenous opiates. This suggests its participation in the control of the stress response.
Characterization of a hyperpolarization-activated cation current in rat pituitary cells
Authors: Simasko S. M. , Sankaranarayanan S.
Published: December 2017

Whole cell patch-clamp techniques were used on clonal pituitary cells (GH3) and primary cultures of somatotrophs and lactotrophs to study currents that would be active at or below voltages for the threshold for action potential generation. When GH3 cells were held at -60 mV and pulsed to -120 mV, a slow-activating sustained inward current was observed (-16.5 +/- 1.5 pA in physiological baths, n = 72; approximately 1 s to half-maximal activation, voltage for 50% activation - 101 mV). The current was insensitive to bath application of 10 mM tetraethylammonium, 10 mM 4-aminopyridine, and 1 mM barium but was completely blocked by 3 mM cesium. The current was found to be a mixed cation current with a sodium permeability of 0.29 relative to potassium. These properties indicate that the current belongs to the hyperpolarization-activated cation current (Ih), or I(f), family of currents. However, the current was not altered by the addition of adenosine 3',5'-cyclic monophosphate (cAMP) to the pipette or forskolin to the bath. A similar but smaller current was observed in 15 of 16 somatotrophs but in only 1 of 9 lactotrophs. Application of cesium to spontaneously spiking GH3 cells or somatotrophs had no effect. However, cesium did block an inward holding current observed at -80 mV. These results demonstrate that the I(h) in pituitary cells does not serve as a pacemaking current but suggest that it may influence membrane potential responses when somatotrophs become hyperpolarized.
Arginine vasopressin and baroreflex function after converting enzyme inhibition in normal humans
Authors: Goldsmith S. R.
Published: December 2017

Arginine vasopressin (AVP) has been shown to interact with sinoaortic and cardiac reflexes under selected experimental conditions. In humans, there is no evidence that AVP potentiates reflex function at modestly increased plasma levels, except possibly if the angiotensin-converting enzyme (ACE) is inhibited. The objective of this study was to test the hypothesis that a modest physiological increase in plasma AVP would potentiate the responses of heart rate (HR), forearm vascular resistance (FVR), plasma norepinephrine (NE), or systemic NE spillover to baroreflex unloading and loading after pretreatment with lisinopril in healthy human volunteers. Seven normal young men were studied on three occasions. Baseline HR, FVR, and steady-state NE kinetics were established, and AVP or vehicle (5% dextrose in water) was infused for 15 min double-blind on the first 2 days. Baroreflexes were then perturbed as follows: 15 min 60 degrees head-up tilt, 15 min 30 degrees head-down tilt plus 1,000 ml normal saline infusion, 15 min 30 degrees head-down tilt plus phenylephrine titrated to raise mean arterial pressure 10-15 mmHg. The study was repeated on a third day 12 h after 5 mg of lisinopril. Five additional subjects underwent similar baroreflex study on 2 days with only lisinopril and placebo. Before baroreflex deactivation and activation in the absence of lisinopril, AVP infusion had no hemodynamic or neurohormonal effects. During AVP infusion after lisinopril, HR decreased from 67 +/- 6.5 to 62 +/- 4.5 beats/min (P < 0.05). AVP had no effect on the response of any variable during baroreflex perturbation relative to vehicle, either with or without lisinopril. Lisinopril had no independent effect on these responses in the additional five subjects. At modestly increased plasma levels, AVP did not affect the responses of HR, FVR, plasma NE, or systemic NE spillover to baroreflex deactivation and activation. After lisinopril, AVP infusion produced a modest bradycardia but still had no significant positive effect on either response. These data suggest that inhibition of the angiotensin-converting enzyme may unmask mild direct or vagally mediated effects of AVP on HR but does not unmask baroreflex potentiation.
Central opioid receptors mediate glucoprivic inhibition of pituitary LH secretion
Authors: Briski K. P.
Published: December 2017

The present studies investigated the significance of glucoprivic metabolic signals, particularly those of central origin, to the regulation of pituitary luteinizing hormone (LH). Groups of gonadectomized (GDX) adult male rats were treated with 2-deoxy-D-glucose (2-DG), an inhibitor of glycolysis, by either intravenous (50, 100, or 200 mg/kg) or intracerebroventricular (5, 20, or 100 microg/rat) administration. Systemic drug treatment caused a significant decrease in mean plasma LH levels compared with saline-treated controls. Intracerebroventricular administration of 2-DG was also efficacious in suppressing circulating LH; animals treated with either of the two highest doses of the drug exhibited a significant reduction in plasma LH. In vitro studies examined direct effects of 2-DG on pituitary gonadotrope secretory activity. Exposure of anterior pituitary tissue to 2-DG during short-term perfusion had no significant impact upon either basal or gonadotropin-releasing hormone-stimulated LH release. Finally, groups of GDX rats were pretreated by intracerebroventricular administration of either the nonselective opioid receptor antagonist, naltrexone, or the selective mu-opioid receptor antagonist, beta-funaltrexamine (beta-FNA), before intravenous injection of 2-DG. Both receptor antagonists were observed to attenuate the suppressive effects of 2-DG on circulating LH in these animals. In summary, treatment of GDX rats with the glucose antimetabolite, 2-DG, decreased plasma LH, suggesting that metabolic signaling of cellular glucose oxidation is of physiological importance to the regulation of pituitary hormone secretion. Findings that plasma LH was diminished in animals treated intracerebroventricularly with 2-DG implicate central glucoprivic receptors in neuroendocrine mechanisms governing the reproductive endocrine axis. Attenuation of 2-DG-induced decreases in circulating LH by opioid receptor antagonists suggests that these receptors, particularly the mu-subtype, mediate central effects of glucoprivation on circulating LH.
Glucose regulation of islet amyloid polypeptide gene expression in rat pancreatic islets
Authors: Gasa R. , Gomis R. , Casamitjana R. , Rivera F. , Novials A.
Published: December 2017

Intracellular pathways by which glucose regulates islet amyloid polypeptide (IAPP) gene expression in pancreatic islets were studied. IAPP mRNA levels were threefold higher in islets cultured with 16.7 mM glucose compared with control (5.5 mM glucose). Mannose and amino acids but not 2-deoxyglucose or 6-deoxyglucose mimicked the effect of glucose. Mannoheptulose (a glycolysis inhibitor) and verapamil and diazoxide (which affect calcium signaling pathway) abolished the difference in islet IAPP mRNA content between high and low glucose. At low glucose, IAPP mRNA levels were increased 1.9-fold in islets treated with forskolin or dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) but not with 12-O-tetradecanoylphorbol 13-acetate. Insulin mRNA levels were 1.6-fold higher in islets cultured at high glucose than controls; glucose metabolism was required, whereas no effects of cAMP or diazoxide were observed. IAPP and insulin were cosecreted into the media. We conclude that glucose regulation of IAPP mRNA abundance requires intracellular metabolism of the hexose and that calcium may serve as a mediator of this effect; cAMP but not protein kinase C possibly participates in this regulation.
Long- and medium-chain triglycerides during parenteral nutrition in critically ill patients
Authors: Delafosse B. , Viale J. P. , Pachiaudi C. , Normand S. , Goudable J. , Bouffard Y. , Annat G. , Bertrand O.
Published: December 2017

Due to their special metabolic pathway, medium-chain triglycerides (MCT) have been claimed to be oxidized more extensively, compared with long-chain triglycerides (LCT), when administered as a parenteral nutritional support. This enhanced lipid oxidation rate of MCT emulsions could be particularly disclosed in hyperglycemic and hyperinsulinemic conditions. In an attempt to further elucidate this question, we measured substrate oxidation rates in critically ill patients liable to experience such metabolic conditions, that is to say postoperative patients after esophageal resection receiving 1.5 times their measured energy expenditure (n = 12) or after liver transplantation (n = 8). These patients received either LCT or MCT-LCT emulsions. The metabolic measurements were performed simultaneously by two methods, namely indirect calorimetry and isotopic methods based on natural abundance of nutrients. Although both groups of patients were hyperglycemic and hyperinsulinemic, the measured carbohydrate and lipid oxidation rates were not different with whatever type of lipid was administered. The MCT-LCT emulsions did not offer clear-cut advantages over LCT emulsions in critically ill patients when lipid energetic fate was considered.
Insulin stimulation of human adipocytes activates the kinase of only a fraction of the insulin receptors
Authors: Klein H. H. , Kowalewski B. , Drenckhan M. , Fehm H. L.
Published: December 2017

The degree of insulin receptor kinase activation by in situ stimulation was studied in isolated human adipocytes. Although maximal in situ stimulation increased the kinase activity approximately 10-fold, this activity could again be doubled by subsequent activation in a cell-free system. To investigate how in situ stimulation resulted in incomplete activation, receptors binding or not binding to anti-phosphotyrosine antibody (alpha-PY) were studied separately. Even after maximal insulin stimulation of the cells, approximately 50% of the receptors did not bind to alpha-PY and had low kinase activity. In the cell-free system, however, these receptors reached activity levels similar to the other receptors, suggesting that they were intact and that factors in their cellular environment had prevented their activation. The activity of the alpha-PY-binding receptors could only be slightly increased in the cell-free system, suggesting that almost complete activation had been attained in situ. In situ stimulation with increasing insulin concentrations increased the number of activated receptors rather than their individual activity. We conclude that factors in the in situ environment prevent insulin activation of approximately 50% of the insulin receptors in human adipocytes and might therefore be important regulators of insulin signaling.
Steady-state and non-steady-state measurements of plasma glutamine turnover in humans
Authors: Kreider M. E. , Stumvoll M. , Meyer C. , Overkamp D. , Welle S. , Gerich J.
Published: December 2017

To compare steady-state glutamine turnover using nitrogen, carbon, and hydrogen tracers and to test the validity of monocompartmental equations to determine plasma glutamine turnover under non-steady-state conditions, we infused 10 normal postabsorptive volunteers simultaneously with [3,4-3H]glutamine, [2-15N]glutamine, and [U-14C]glutamine for 4 h to isotopic steady state. Eight of the ten subjects were subsequently infused in a stepwise fashion with exogenous glutamine. Plasma glutamine enrichment and specific activities fit a monoexponential model well (r = 0.89, 0.92, and 0.92 for [2-15N]-, [U-14C]-, and [3,4-3H]glutamine, respectively). Volumes of distribution for each tracer (362 +/- 58, 433 +/- 51, and 446 +/- 63 ml/kg) and the transfer rate constants (0.0224 +/- 0.0020, 0.0222 +/- 0.0020, and 0.0240 +/- 0.0023 min(-1)) for [2-15N]-, [U-14C]-, and [3,4-3H]glutamine, respectively, were not significantly different from one another. However, turnover of glutamine determined with [3,4-3H]glutamine (6.14 +/- 0.54 micromol x kg(-1) x min(-1)) exceeded that determined with [U-14C]glutamine (5.72 +/- 0.541 micromol x kg(-1) x min(-1); P < 0.03), which in turn exceeded that determined with [2-15N]glutamine (4.67 +/- 0.39 micromol x kg(-1) x min(-1), P < 0.01). The monocompartmental non-steady-state equations of both DeBodo et al. (DeBodo, R., R. Steele, A. Dunn, and J. Bishop. Rec. Prog. Horm. Res. 19: 445-448, 1963) and Finegood et al. (Finegood, D., R. Bergman, and M. Vranic. Diabetes 36: 914-924, 1987) yielded acceptable approximations of predicted rates of glutamine plasma appearance with deviations from predicted rates from 0.2 to 1.6% (Finegood et al.) and from 0.1 to 8.2% (DeBodo et al.). Use of a 0.75 pool fraction most closely approximated predicted rates.
Whole body and splanchnic metabolic and circulatory effects of glucose during beta-adrenergic receptor inhibition
Authors: Brundin T. , Aksnes A. K. , Wahren J.
Published: December 2017

The aim of the study was to assess the possible contribution of adrenergic mechanisms to the thermogenic and circulatory effects of glucose ingestion. With the use of indirect calorimetry and arterial, pulmonary arterial, and hepatic venous catheterization, whole body and splanchnic oxygen uptake and blood flow were examined in nine propranolol-treated healthy male volunteers before and during 2 h after oral ingestion of 75 g of glucose. The glucose effects were compared with those in nine untreated controls. After propranolol, the glucose-induced rise in splanchnic blood flow was reduced by approximately 60%, and the hepatic venous glucose release to the systemic circulation was significantly delayed. Glucose-induced increments in pulmonary and splanchnic oxygen uptake and cardiac output were similar in the two groups. It is concluded that adrenergic mechanisms contribute to the glucose-induced rise in splanchnic blood flow and thereby probably to the time course for intestinal absorption of nutrients. It is suggested that the magnitude of glucose-induced thermogenesis is independent of adrenergic stimulation.
Intrauterine growth restriction does not alter response of protein synthesis to feeding in newborn pigs
Authors: Davis T. A. , Fiorotto M. L. , Burrin D. G. , Pond W. G. , Nguyen H. V.
Published: December 2017

This study aimed to determine the effect of intrauterine growth restriction (IUGR) on the acute response of tissue protein synthesis to feeding in newborn pigs. Newborn pigs of sows fed either control or protein-restricted diets throughout gestation were designated C or IUGR, respectively. Both groups were either fasted for 9 h after birth or fed hourly 30 ml colostrum/kg body wt for 2.75 h after a 6-h fast. Fractional rates of tissue protein synthesis (Ks) were measured in vivo with a flooding dose of L-[4-3H]phenylalanine. Birth weight was reduced by 33% in IUGR pigs. IUGR had no effect on Ks in skeletal muscles, heart, liver, jejunum, or pancreas. Feeding stimulated tissue Ks similarly in C and IUGR pigs. Fasting plasma insulin concentrations and their rise with feeding were unaffected by IUGR. Plasma insulin-like growth factor I (IGF-I) concentrations were reduced by 42% in IUGR pigs and were not altered by feeding in either IUGR or C pigs. There were positive nonlinear relationships between tissue Ks and circulating concentrations of insulin. The results indicate that, in newborn pigs, tissue Ks are unaffected by IUGR, despite reduced plasma IGF-I concentrations. The efficiency with which nutrients stimulate tissue Ks is also not altered by IUGR, perhaps because the rise in plasma insulin concentrations with feeding is unaffected by IUGR.
Placental transport of threonine and its utilization in the normal and growth-restricted fetus
Authors: Anderson A. H. , Fennessey P. V. , Meschia G. , Wilkening R. B. , Battaglia F. C.
Published: December 2017

Placental transport and fetoplacental utilization of threonine (Thr) were compared at 130 +/- 1 days gestational age between seven control ewes (C) and six ewes in which intrauterine growth restriction (IUGR) had been induced by exposure to high ambient temperature from 33 +/- 1 to 112 +/- 2 days of gestation. The fluxes were measured using simultaneous intravenous infusions of L-[1-13C]Thr into the mother and L-[U-14C]Thr into the fetus. The IUGR group had less fetal weight (1.27 +/- 0.14 vs. 3.10 +/- 0.10 kg, P < 0.01) and placental weight (120 +/- 17 vs. 295 +/- 14 g, P < 0.01) than the C group. The direct flux of maternal Thr into the fetal systemic circulation was less in the IUGR fetuses, both relative to fetal weight (1.40 +/- 0.19 vs. 2.19 +/- 0.18 mumol.min-1.kg fetus-1, P = 0.0107) and placental weight (1.5 +/- 0.2 vs. 2.3 +/- 0.2 mumol.min-1.100 g placenta-1, P = 0.0187). In both groups, there was excretion of CO2 produced from fetal Thr. The rate of CO2 production from fetal plasma Thr carbon by fetus plus placenta was reduced in the IUGR group (1.50 +/- 0.23 vs. 2.86 +/- 0.32 mumol.min-1.kg fetus-1, P = 0.0065). We conclude that the flux of maternal Thr into the IUGR fetus is markedly reduced because of a reduction in placental mass and because of a weight-specific reduction in Thr placental transport. The reduced flux is routed into fetal Thr accretion via a decrease in fetal Thr oxidation.
Oxidant stress reduces insulin responsiveness in 3T3-L1 adipocytes
Authors: Rudich A. , Kozlovsky N. , Potashnik R. , Bashan N.
Published: December 2017

Increased oxidant stress has been suggested to occur in diabetes and to contribute to the development of late diabetic complications. Whether oxidant stress plays a role in the development or progression of insulin resistance is not known. In this study we hypothesized that exposing 3T3-L1 adipocytes to prolonged micromolar concentrations of H2O2 would reduce their acute metabolic responses to insulin stimulation. 3T3-L1 adipocytes exposed to 25 mU/ml glucose oxidase (GO) for 18 h exhibited a threefold increase in basal 2-deoxyglucose (2-DG) uptake activity. However, net increase in 2-DG uptake activity after acute insulin (100 nM) stimulation was 355 +/- 56 pmol.mg protein-1.min-1 in control vs. 198 +/- 41 pmol.mg protein-1.min-1 in GO-pretreated cells (P < 0.05). Basal lipogenesis activity was significantly enhanced by GO, but acute insulin stimulation resulted in significantly reduced lipogenesis activity (29 +/- 4 vs. 11 +/- 1 nmol glucose/well for control and 50 mU/ml GO, respectively, P = 0.001). Glycogen synthase alpha activity was reduced by GO (78 +/- 1 vs. 43 +/- 2 pmol UDP-glucose.mg protein-1.min-1, P = 0.03), whereas insulin stimulation of glycogen synthase was reduced, exhibiting a right shift in the insulin dose-response curve. These effects of GO were associated with increased GLUT-1 and reduced GLUT-4 protein and mRNA content. In conclusion, our data suggest that oxidant stress alters glucose transporters expression and insulin-stimulated metabolism in 3T3-L1 adipocytes.
17 beta-Estradiol modulation of glucose transporter 1 expression in blood-brain barrier
Authors: Shi J. , Simpkins J. W.
Published: December 2017

The present study was designed to evaluate 17 beta-estradiol (E2) modulation of glucose transporter 1 (GLUT-1) protein and mRNA expression in blood-brain barrier (BBB) endothelium. Female rats were ovariectomized (OVX) for 12-14 days, then E2 was injected at dosages of 1-100 micrograms/kg sc at 2-16 h before sampling. Glucose transport into BBB endothelial cells was assessed using 2-deoxy-[14C]glucose (2-[14C]DG) uptake. GLUT-1 protein and mRNA samples were analyzed by Western and Northern blotting, respectively. E2 treatment caused dose- and time-dependent increases in 2-[14C]DG uptake and GLUT-1 protein expression by microvessels. The peak responses were induced by 10 micrograms/kg E2 dose at the 4-h sampling time (36.0 and 31.3% increases, P < 0.05, respectively). GLUT-1 mRNA demonstrated a transient increase at 15 min (55%, P < 0.05), then decreased to basal level by 2 h. This study shows that in vivo treatment with E2 increases 2-[14C]DG uptake into the BBB endothelial cells and suggests this E2 effect is due to its modulation of GLUT-1 mRNA and protein.
Effects of leucine on whole body leucine, valine, and threonine metabolism in humans
Authors: Hoffer L. J. , Taveroff A. , Robitaille L. , Hamadeh M. J. , Mamer O. A.
Published: December 2017

We tested whether expansion of the plasma leucine pool distorts leucine or valine tracer kinetics, causing errors in the derived values of whole body proteolysis. Seven normal adults received a 10-h primed-continuous tracer infusion of L-[5,5,5-2H3]leucine, L-[(1-13)C]valine, and L-[(1-13)C]threonine, during the final 7 h of which L-leucine was infused at a rate that more than tripled the plasma leucine concentration. Leucine, valine, and threonine rates of appearance were converted to a common value of whole body proteolysis on the basis of their concentrations in body proteins. The conversion of labeled leucine and valine to their corresponding branched-chain alpha-keto and alpha-hydroxy acids was also monitored. Before the unlabeled leucine infusion, postabsorptive whole body proteolysis was estimated similarly by the three tracers (approximately 180 mg protein.kg-1.h-1. The leucine infusion reduced proteolysis by an average of 21% (P < 0.006), as estimated by use of valine or threonine kinetics, and by 10% by use of leucine kinetics (P < 0.02). No delay in the conversion of valine to alpha-ketoisovalerate occurred during the leucine infusion. Thus all three tracers indicated similar postabsorptive rates of whole body proteolysis and a reduction of proteolysis during leucine administration, although the magnitude of the effect was underestimated with use of the leucine tracer.
Lipolytic responsiveness to epinephrine in nondiabetic and diabetic humans
Authors: Divertie G. D. , Jensen M. D. , Cryer P. E. , Miles J. M.
Published: December 2017

To determine whether the sensitivity of adipose tissue lipolysis to catecholamines is increased in poorly controlled insulin-dependent diabetes, the lipolytic response to epinephrine was measured in seven nondiabetic volunteers and seven poorly controlled diabetic subjects with use of [1-(14)C]palmitate as a tracer. Subjects received sequential 1-h infusions of epinephrine, which produced epinephrine concentrations of approximately 1,000, approximately 1,750, approximately 3,500, and approximately 6,000 pmol/l. A pancreatic clamp was used to maintain constant plasma hormone levels. Concentration-response curves were constructed for each subject from the integrated lipolytic response during each epinephrine infusion. There was no difference in maximal lipolytic response (117 +/- 19 vs. 152 +/- 11 mumol.kg-1.h-1) or in maximally effective (3,171 +/- 267 vs. 3,357 +/- 349 pmol/l) or half-maximally effective (1,081 +/- 109 vs. 1,015 +/- 120 pmol/l) epinephrine concentrations between nondiabetic and diabetic subjects, respectively (all P = NS). In control subjects, maximum beta-hydroxybutyrate concentrations were achieved at lower epinephrine concentrations than those required for a maximum lipolytic effect. Thus, under pancreatic clamp conditions, the lipolytic response to epinephrine in nondiabetic and diabetic subjects was similar.
Lactate production by swine adipocytes: effects of age, nutritional status, glucose concentration, and insulin
Authors: Heckler B. K. , Carey G. B.
Published: December 2017

To develop an alternative model in which to study the relationship between adipose tissue lactate production, obesity, and non-insulin-dependent diabetes mellitus (NIDDM), we investigated lactate production by swine adipocytes. Subcutaneous adipocytes from fasted 3-wk-old, fasted 7-mo-old, and fed 7-mo-old Yucatan minIature swine were isolated and incubated with 0.2, 1, 5, 10, or 25 mM glucose +/- 1 mU/ml insulin. Total glucose metabolism (TGM) was estimated by product summation. Results showed that 1) TGM was threefold greater in cells from fasted 7-mo- vs. 3-wk-old swine (P < 0.05), 2) TGM was 2.7-fold greater in cells from fed 7-mo-old vs. fasted 7-mo-old swine (P < 0.05), 3) insulin failed to stimulate TGM in adipocytes from swine of either age and either nutritional status, and 4) lactate and pyruvate accounted for 34 and 30% of TGM, respectively, in adipocytes from swine of both ages. Similarities in glucose metabolism and lactate production in adipocytes from swine and obese NIDDM humans make the swine a potentially valuable model for studying lactate production associated with obesity and NIDDM.
Dynamic aspects for interislet synchronization of oscillatory insulin secretions
Authors: Yao N. K. , Chang L. W. , Lin B. J. , Kuo T. S.
Published: December 2017

How are the oscillatory insulin secretions from numerous islets synchronized to result in an identifiable oscillation? We postulated that a sudden increase in glucose concentration could best account for the interislet synchronization. The perifusion with two parallel chambers each containing 100 islets from the same rat was performed. The glucose concentrations of two chambers were simultaneously increased from 100 to 300 mg/dl in step function to examine the synchronizing efficacy. Synchrony and regularity of insulin oscillation were evaluated by cross-correlation and/or power spectral analysis. Although the insulin had been in stable oscillation, we found that the synchrony between two chambers and the regularity of each chamber were still significantly improved after a sudden increase in glucose level. However, the improved synchrony and regularity were transient. They gradually slid toward a less rigorous condition in a 15-h long-term perifusion. We suggested that the interislet synchronization of oscillatory insulin secretions could be improved by a sudden increase in glucose level. The insulin pulses were therefore enhanced to present their physiological effects.
An abundant supply of amino acids enhances the metabolic effect of exercise on muscle protein
Authors: Biolo G. , Tipton K. D. , Klein S. , Wolfe R. R.
Published: December 2017

Six normal untrained men were studied during the intravenous infusion of a balanced amino acid mixture (approximately 0.15 g.kg-1.h-1 for 3 h) at rest and after a leg resistance exercise routine to test the influence of exercise on the regulation of muscle protein kinetics by hyperaminoacidemia. Leg muscle protein kinetics and transport of selected amino acids (alanine, phenylalanine, leucine, and lysine) were isotopically determined using a model based on arteriovenous blood samples and muscle biopsy. The intravenous amino acid infusion resulted in comparable increases in arterial amino acid concentrations at rest and after exercise, whereas leg blood flow was 64 +/- 5% greater after exercise than at rest. During hyperaminoacidemia, the increases in amino acid transport above basal were 30-100% greater after exercise than at rest. Increases in muscle protein synthesis were also greater after exercise than at rest (291 +/- 42% vs. 141 +/- 45%). Muscle protein breakdown was not significantly affected by hyperminoacidemia either at rest or after exercise. We conclude that the stimulatory effect of exogenous amino acids on muscle protein synthesis is enhanced by prior exercise, perhaps in part because of enhanced blood flow. Our results imply that protein intake immediately after exercise may be more anabolic than when ingested at some later time.
Involvement of capsaicin-sensitive nerves in regulating the hormone and glucose metabolic response to endotoxin
Authors: Morgan A. E. , Lang C. H.
Published: December 2017

This study investigated the role that sensory nerves play in mediating the hormone and glucose metabolic response to endotoxin [lipopolysaccharide (LPS)]. Adult rats were pretreated subcutaneously with capsaicin to selectively destroy primary sensory afferent nerve fibers. Ten days later, [3-3H]glucose was infused intravenously to assess whole body glucose flux before and after the intravenous injection of Escherichia coli LPS (100 micrograms/100 g body wt). Control animals responded to LPS with characteristic increases in the plasma concentration of glucose (91%) and lactate (threefold) and elevations in the rates of glucose appearance and disappearance (77%). In capsaicin-treated rats, the maximal LPS-induced increase in these parameters was attenuated by 50-60%. In addition, these animals were hypoglycemic at the conclusion of the experiment. Control animals demonstrated early and sustained elevations in circulating levels of corticosterone, glucagon, and catecholamines. In contrast, the early LPS-induced elevation in epinephrine and norepinephrine, and to a lesser extent glucagon, was completely absent or greatly impaired by capsaicin pretreatment. In a separate study, the epinephrine-induced increase in glucose flux was blunted by 75% in capsaicin-treated rats. These data indicate that sensory afferent neurons play a critical role in the early secretory response of glucagon and catecholamines, the maintenance of tissue catecholamine responsiveness, and the stimulation of glucose production after LPS.
Tumor necrosis factor activity of pancreatic islets
Authors: Leeper-Woodford S. K. , Tobin B. W.
Published: December 2017

Tumor necrosis factor (TNF) is involved in the pathogenesis of acute sepsis-induced organ injury and has been implicated as a mediator of metabolic alterations observed during sepsis. Pancreatic islet cell function may be significantly compromised during sepsis or endotoxemia, and sepsis also increases plasma levels of epinephrine, a modifier of islet insulin secretion. We proposed that islets exposed to bacterial lipopolysaccharide (LPS) produce TNF and that epinephrine attenuates islet secretory activity. We monitored the effects of LPS and epinephrine on TNF and insulin activity of isolated Wistar-Furth rat islets (pancreas digested with collagenase, islets isolated using Ficoll gradients; n = 4 islet populations, each with 632 +/- 11 islets/2.5 ml culture medium). Islets were incubated (37 degrees C, 5% CO2) 3 days. LPS (Escherichia coli, 1 microgram/ml) and epinephrine (14 micrograms/ml) were added to the islets, and incubations were continued for 1-4 h. Glucose (Beckman Glucose Analyzer), insulin (radioimmunoassay), and TNF (L929 cytotoxicity assay) were measured in the islet medium samples at 1- to 4-h time points. In the conditioned medium, glucose decreased (P < 0.05), insulin increased (P < 0.05), and exposure to LPS did not alter these levels [P = not significant (NS)] but did increase TNF activity by 400% (P < 0.05). Epinephrine reduced insulin by 38-43% (P < 0.05) and TNF by 20-25% (P < 0.05) but had no effect on glucose levels (P = NS). We conclude that insulin is secreted from isolated islets and that exposure to LPS acutely increases islet-derived TNF activity, whereas epinephrine modifies TNF and insulin secretion of rat pancreatic islets.
Tissue triglycerides, insulin resistance, and insulin production: implications for hyperinsulinemia of obesity
Authors: Koyama Kazunori , Chen Guoxun , Lee Young , Unger Roger H.
Published: December 2017

Obesity is associated with both insulin resistance and hyperinsulinemia. Initially hyperinsulinemia compensates for the insulin resistance and thereby maintains normal glucose homeostasis. Obesity is also associated with increased tissue triglyceride (TG) content. To determine whether both insulin resistance and hyperinsulinemia might be secondary to increased tissue TG, we studied correlations between TG content of skeletal muscle, liver, and pancreas and plasma insulin, plasma [insulin] × [glucose], and β-cell function in four rat models with widely varying fat content: obese Zucker diabetic fatty rats, free-feeding lean Wistar rats, hyperleptinemic Wistar rats with profound tissue lipopenia, and rats pair fed to hyperleptinemics. Correlation coefficients >0.9 ( P < 0.05) were obtained among TG of skeletal muscle, liver, and pancreas and among plasma insulin, [insulin] × [glucose] product, and β-cell function as gauged by basal, glucose-stimulated, and arginine-stimulated insulin secretion by the isolated perfused pancreas. Although these correlations cannot prove cause and effect, they are consistent with the hypothesis that the TG content of tissues sets the level of both insulin resistance and insulin production.
Interleukin-8 can mediate acute-phase protein production by isolated human hepatocytes
Authors: Wigmore Stephen J. , Fearon Kenneth C. H. , Maingay Jean P. , Lai Paul B. S. , Ross James A.
Published: December 2017

During the course of studies designed to identify the role of cytokines in the reprioritization of hepatic protein synthesis associated with cachexia we detected a hepatocyte-stimulating moiety in the supernatants of pancreatic cancer cells that was unrelated to interleukin (IL)-6. This study identifies that moiety as IL-8 and investigates the role of IL-8 in the induction of acute-phase protein production. The human pancreatic cancer cell line MIA PaCa-2 produced >1 ng/ml of IL-8 per 24 h, and supernatants from this cell line induced C-reactive protein (CRP) production from isolated human hepatocytes. Addition of neutralizing anti-human IL-8 antibody to such supernatants produced almost complete inhibition of CRP production. The addition of recombinant human IL-8 to hepatocytes resulted in a dose-dependent increase in CRP, α1-acid glycoprotein, and α1-antichymotrypsin production and a decrease in the production of transferrin and prealbumin. This study demonstrates that recombinant or tumor-derived IL-8 can modulate acute-phase protein production from isolated human hepatocytes and from human hepatoma cells.
Fatty acids reduce heparin-releasable LPL activity in cultured cardiomyocytes from rat heart
Authors: Anderson Lorraine G. , Carroll Rogayah , Ewart H. Stephen , Acharya Anjli , Severson David L.
Published: December 2017

Varying glucose and fatty acid (FA) concentrations in the medium of cultured cardiomyocytes from adult rat hearts were tested for effects on lipoprotein lipase (LPL) activity. Glucose (5.5, 11, and 25 mM in the culture medium for 18–22 h) had no effect on either heparin-releasable LPL (HR-LPL) or on cellular LPL (C-LPL) activities. When cardiomyocytes were cultured overnight with 60 μM oleate, HR-LPL activity was reduced to 20% of control, with no change in C-LPL activity or total C-LPL mass. Similar results (HR-LPL and C-LPL activities) were obtained with 60 μM concentrations of palmitate and myristate; linoleate and eicosapentaenoate did reduce C-LPL activity, but the decrease in HR-LPL activity was much greater. Oxfenicine, an FA oxidation inhibitor, did not alter the inhibitory effect of 60 μM oleate on HR-LPL. Short-term incubations (1 and 3 h) of cultured cardiomyocytes with 60 μM oleate did not displace LPL into the medium. Immunodetectable LPL on the cell surface of oleate-treated cultured cardiomyocytes was increased compared with control cells, but heparin treatment released the same amount of LPL mass that had reduced catalytic activity.
Role of hepatic α- and β-adrenergic receptor stimulation on hepatic glucose production during heavy exercise
Authors: Coker Robert H. , Krishna Mahesh G. , Lacy D. Brooks , Bracy Deanna P. , Wasserman David H.
Published: December 2017

The role of catecholamines in the control of hepatic glucose production was studied during heavy exercise in dogs, using a technique to selectively block hepatic α- and β-adrenergic receptors. Surgery was done >16 days before the study, at which time catheters were implanted in the carotid artery, portal vein, and hepatic vein for sampling and the portal vein and vena cava for infusions. In addition, flow probes were implanted on the portal vein and hepatic artery. Each study consisted of a 100-min equilibration, a 30-min basal, a 20-min heavy exercise (∼85% of maximum heart rate), a 30-min recovery, and a 30-min adrenergic blockade test period. Either saline (control; n= 7) or α (phentolamine)- and β (propranolol)-adrenergic blockers (Blk; n = 6) were infused in the portal vein. In both groups, epinephrine (Epi) and norepinephrine (NE) were infused in the portal vein during the blockade test period to create supraphysiological levels at the liver. Isotope ([3-3H]glucose) dilution and arteriovenous differences were used to assess hepatic function. Arterial Epi, NE, glucagon, and insulin levels were similar during exercise in both groups. Endogenous glucose production (Ra) rose similarly during exercise to 7.9 ± 1.2 and 7.5 ± 2.0 mg ⋅ kg−1⋅ min−1in control and Blk groups at time = 20 min. Net hepatic glucose output also rose to a similar rate in control and Blk groups with exercise. During the blockade test period, arterial plasma glucose and Rarose to 164 ± 5 mg/dl and 12.0 ± 1.4 mg ⋅ kg−1⋅ min−1, respectively, but were essentially unchanged in Blk. The attenuated response to catecholamine infusion in Blk substantiates the effectiveness of the hepatic adrenergic blockade. In conclusion, these results show that direct hepatic adrenergic stimulation does not participate in the increase in Ra, even during the exaggerated sympathetic response to heavy exercise.
Inhibition of glycogenolysis enhances gluconeogenic precursor uptake by the liver of conscious dogs
Authors: Shiota Masakazu , Jackson Patricia A. , Bischoff Hilmar , McCaleb Michael , Scott Melanie , Monohan Michael , Neal Doss W. , Cherrington Alan D.
Published: December 2017

We investigated the effect of inhibiting glycogenolysis on gluconeogenesis in 18-h-fasted conscious dogs with the use of intragastric administration of BAY R 3401, a glycogen phosphorylase inhibitor. Isotopic ([3-3H]glucose and [U-14C]alanine) and arteriovenous difference methods were used to assess glucose metabolism. Each study consisted of a 100-min equilibration, a 40-min control, and two 90-min test periods. Endogenous insulin and glucagon secretions were inhibited with somatostatin (0.8 μg ⋅ kg−1 ⋅ min−1), and the two hormones were replaced intraportally (insulin: 0.25 mU ⋅ kg−1 ⋅ min−1; glucagon: 0.6 ng ⋅ kg−1 ⋅ min−1). Drug (10 mg/kg) or placebo was given after the control period. Insulin and glucagon were kept at basal levels in the first test period, after which glucagon infusion was increased to 2.4 ng ⋅ kg−1 ⋅ min−1; BAY R 3401 decreased tracer-determined endogenous glucose production [rate of glucose production (Ra): 14 ± 1 to 7 ± 1 μmol ⋅ kg−1 ⋅ min−1] and net hepatic glucose output (11 ± 1 to 3 ± 2 μmol ⋅ kg−1 ⋅ min−1) during test 1. It increased the net hepatic uptake of gluconeogenic substrates from 9.0 ± 2.0 to 11.6 ± 0.6 μmol ⋅ kg−1 ⋅ min−1. Basal glycogenolysis was decreased by drug (9.1 ± 0.7 to 1.5 ± 0.2 μmol glucosyl U ⋅ kg−1 ⋅ min−1). Placebo had no effect on Ra or the uptake of gluconeogenic precursors by the liver. The rise in glucagon increased Ra by 22 ± 3 and by 8 ± 2 μmol ⋅ kg−1 ⋅ min−1(at 10 min) in placebo and drug, respectively. The rise in glucagon caused little change in the net hepatic uptake (μmol ⋅ kg−1 ⋅ min−1) of gluconeogenic substrates in placebo (8.2 ± 0.6 to 9.0 ± 1.0) but increased it markedly (11.6 ± 0.6 to 15.4 ± 1.0) in drug. Glucagon increased glycogenolysis by 22.1 ± 2.5 and by 7.8 ± 1.6 μmol ⋅ kg−1 ⋅ min−1in placebo and drug, respectively. The amount of glycogen (μmol glucosyl U/kg) synthesized from gluconeogenic carbon was four times higher in drug (48.6 ± 9.7) than in placebo (11.3 ± 1.7). We conclude that BAY R 3401 caused a marked reduction in basal and glucagon-stimulated glycogenolysis. As a result of these changes, there was an increase in the net hepatic uptake of gluconeogenic precursors and in glycogen synthesis.
Expression of a single gene produces both forms of skeletal muscle cyclic nucleotide-gated channels
Authors: Santy Lorraine C. , Guidotti Guido
Published: December 2017

Cyclic nucleotide-gated cation channels in skeletal muscle are responsible for insulin-activated sodium entry into this tissue (J. E. M. McGeoch and G. Guidotti. J. Biol. Chem. 267: 832–841, 1992). These channels have previously been isolated from rabbit skeletal muscle by 8-bromoguanosine 3′,5′-cyclic monophosphate (8-BrcGMP) affinity chromatography, which separates them into two populations differing in nucleotide affinity [L. C. Santy and G. Guidotti. Am. J. Physiol. 271 ( Endocrinol. Metab. 34): E1051-E1060, 1996]. In this study, a polymerase chain reaction approach was used to identify skeletal muscle cyclic nucleotide-gated channel cDNAs. Rabbit skeletal muscle expresses the same cyclic nucleotide-gated channel as rabbit aorta (M. Biel, W. Altenhofen, R. Hullin, J. Ludwig, M. Freichel, V. Flockerzi, N. Dascal, U. B. Kaupp, and F. Hofmann. FEBS Lett. 329: 134–138, 1993). The entire cDNA for this gene was cloned from rabbit skeletal muscle and an antiserum to this protein produced. Expression of this cDNA produces a 63-kDa protein with cyclic nucleotide-gated channel activity. A similarly sized immunoreactive protein is present in sarcolemma. Purification of the expressed channels reveals that this single gene produces both native skeletal muscle channel populations.
Protein depletion and replenishment in mice: different roles of muscle and liver
Authors: Scornik Oscar A. , Howell Scott K. , Botbol Violeta
Published: December 2017

Fully grown male CD-1 mice, fed a protein-free diet for 3 days, received 1 g of starch with or without 300 mg casein by intragastric intubation. We surveyed the acute effects of these nutrients on protein synthesis in all tissues (by extrapolating to infinity the incorporation of radioactive leucine after its injection in massive doses) and protein degradation in skeletal muscle and liver (by the accumulation of bestatin-induced peptide intermediates). Muscle proteolysis was the major source of N during depletion. Compared with postabsorptive animals, starch suppressed muscle protein loss (synthesis +21%, degradation −24%, P < 0.01) and stimulated hepatic proteolysis (degradation +28%, P < 0.01). Addition of casein to the starch was anabolic in liver (synthesis +41%, degradation −33%, P < 0.01), gastrointestinal tract, pancreas, and skin (synthesis +38, +69 and +38%, respectively, P < 0.01) but had no effect on muscle. Protein turnover proved uniquely sensitive to the dietary supply of carbohydrates in muscle and to the endogenous or exogenous supply of amino acids in liver.