bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulation by iodide of H2O2generation in thyroid slices from several species
Authors: Corvilain B. , Collyn L. , van Sande J. , Dumont J. E.
Published: December 2017

The regulation of thyroid metabolism by iodide involves numerous inhibitory effects. However, in unstimulated dog thyroid slices, a small inconstant stimulatory effect of iodide on H2O2 generation is observed. The only other stimulatory effect reported with iodide is on [1-14C]glucose oxidation, i.e., on the pentose phosphate pathway. Because we have recently demonstrated that the pentose phosphate pathway is controlled by H2O2generation, we study here the effect of iodide on basal H2O2 generation in thyroid slices from several species. Our data show that in sheep, pig, bovine, and to a lesser extent dog thyroid, iodide had a stimulatory effect on H2O2 generation. In horse and human thyroid, an inconstant effect was observed. We demonstrate in dogs that the stimulatory effect of iodide is greater in thyroids deprived of iodide, raising the possibility that differences in thyroid iodide pool may account, at least in part, for the differences between the different species studied. This represents the first demonstration of an activation by iodide of a specialized thyroid function. In comparison with conditions in which an inhibitory effect of iodide on H2O2 generation is observed, the stimulating effect was observed for lower concentrations and for a shorter incubation time with iodide. Such a dual control of H2O2 generation by iodide has the physiological interest of promoting an efficient oxidation of iodide when the substrate is provided to a deficient gland and of avoiding excessive oxidation of iodide and thus synthesis of thyroid hormones when it is in excess. The activation of H2O2 generation may also explain the well described toxic effect of acute administration of iodide on iodine-depleted thyroids.
Threonine dehydrogenase is a minor degradative pathway of threonine catabolism in adult humans
Authors: Darling Pauline B. , Grunow John , Rafii Mahroukh , Brookes Steve , Ball Ronald O. , Pencharz Paul B.
Published: December 2017

The threonine dehydrogenase (TDG) pathway is a significant route of threonine degradation, yielding glycine in experimental animals, but has not been accurately quantitated in humans. Therefore, the effect of a large excess of dietary threonine, given either as free amino acid (+Thr) or as a constituent of protein (+P-Thr), on threonine catabolism to CO2and to glycine was studied in six healthy adult males using a 4-h constant infusion ofl-[1-13C]threonine and [15N]glycine. Gas chromatography-combustion isotope ratio mass spectrometry was used to determine [13C]glycine produced from labeled threonine. Threonine intakes were higher on +Thr and +P-Thr diets compared with control (126, 126, and 50 μmol ⋅ kg−1⋅ h−1, SD 8, P < 0.0001). Threonine oxidation to CO2increased threefold in subjects on +Thr and +P-Thr vs. control (49, 45, and 15 μmol ⋅ kg−1⋅ h−1, SD 6, P < 0.0001). Threonine conversion to glycine tended to be higher on +Thr and +P-Thr vs. control (3.5, 3.4, and 1.6 μmol ⋅ kg−1⋅ h−1, SD 1.3, P = 0.06). The TDG pathway accounted for only 7–11% of total threonine catabolism and therefore is a minor pathway in the human adult.
The differential effects of galanin-(1—30) and -(3—30) on anterior pituitary hormone secretion in vivo in humans
Authors: Todd Jeannie F. , Edwards C. Mark B. , Ghatei Mohammad A. , Bloom Stephen R.
Published: December 2017

Intravenous injection of galanin increases plasma growth hormone (GH) and prolactin (PRL) concentrations. In the rat, the effects of galanin on GH appear to be mediated via the hypothalamic galanin receptor GAL-R1, at which galanin-(3—29) is inactive. In contrast, the effect of galanin on PRL is mediated via the pituitary-specific galanin receptor GAL-RW, at which galanin-(3—29) is fully active. We investigated the effects of an intravenous infusion of human galanin (hGAL)-(1—30) and -(3—30) on anterior pituitary hormone levels in healthy females. Subjects were infused with saline, hGAL-(1—30) (80 pmol ⋅ kg− 1 ⋅ min− 1), and hGAL-(3—30) (600 pmol ⋅ kg− 1 ⋅ min− 1) and with boluses of gonadotropin-releasing hormone, thyrotropin-releasing hormone, and growth hormone-releasing hormone (GHRH). Both hGAL-(1—30) and -(3—30) potentiated the rise in GHRH-stimulated GH levels [area under the curve (AUC), saline, 2,810 ± 500 vs. hGAL-(1—30), 4,660 ± 737, P < 0.01; vs. hGAL-(3—30), 6,870 ± 1,550 ng ⋅ min ⋅ ml− 1, P < 0.01]. In contrast to hGAL-(1—30), hGAL-(3—30) had no effect on basal GH levels (AUC, saline, −110 ± 88 vs. hGAL 1—30, 960 ± 280, P < 0.002; vs. hGAL-(3—30), 110 ± 54 ng ⋅ min ⋅ ml− 1, P = not significant). These data suggest that the effects of galanin on basal and stimulated GH release are mediated via different receptor subtypes and that the human equivalent of GAL-RW may exist.
Effects of nicotinic acid on fatty acid kinetics, fuel selection, and pathways of glucose production in women
Authors: Wang Wei , Basinger Alice , Neese Richard A. , Christiansen Mark , Hellerstein Marc K.
Published: December 2017

Chronic nicotinic acid (NA) ingestion effectively lowers lipid levels, but adverse effects on glucose metabolism have been reported. Our goal was to investigate acute and chronic effects of NA on lipolysis and glucose metabolism in women. Healthy normolipidemic volunteers ( n = 5) were studied twice; four-day hospital stays were separated by 1 mo, during which time subjects took increasing doses of NA to 2 g/day (500 mg, 4 times). In the second study, 500 mg of NA was given at 0800. Rates of appearance (Ra) of free fatty acid (FFA), glycerol, and glucose were determined by isotope dilution (of [1,2,3,4-13C4]palmitate, [2-13C1]glycerol, and [U-13C6]glucose). Mass isotopomer distribution analysis was used to measure gluconeogenesis and glycogenolysis. Fasting FFA concentrations ([FFA]), RaFFA, and Raglycerol were nonsignificantly elevated after 1 mo. Acute NA induced a significant reduction followed by a rebound overshoot of [FFA], RaFFA, and Raglycerol. Whole body fat oxidation fell initially and then increased back to basal levels; endogenous glucose production (EGP) increased in parallel with carbohydrate oxidation and then returned to basal values. The increased EGP was due entirely to increased glycogenolysis, not gluconeogenesis. We conclude that chronic effects of NA on FFA metabolism are complex (acute suppression followed by overshoot of RaFFA and [FFA] on top of a trend toward basal elevations), that responses after NA are consistent with operation of a glucose-fatty acid cycle in peripheral tissues, and that secondary effects on EGP were through changes in glycogenolysis, not gluconeogenesis.
The relationship between creatine kinase kinetics and exercise intensity in human forearm is unchanged by age
Authors: Horská A. , Fishbein K. W. , Fleg J. L. , Spencer R. G. S.
Published: December 2017

Using31P magnetic resonance spectroscopy, creatine kinase (CK) reaction kinetics was assessed in the forearm flexor digitorum profundus muscle of healthy young ( n = 11, age 34.7 ± 5 yr) and older ( n = 20, age 73.5 ± 8 yr) subjects at rest, intermittent exercise at 20% maximum voluntary contraction (MVC), and 40% MVC. Exercise resulted in a significant increase in the average ratio of inorganic phosphate (Pi) to phosphocreatine (PCr) from resting values of 0.073 ± 0.031 (young) and 0.082 ± 0.037 (older) to 0.268 ± 0.140 (young, P < 0.01) and 0.452 ± 0.387 (older, P < 0.01) at 40% MVC. At 40% MVC, intracellular pH decreased significantly, from resting values of 7.08 ± 0.08 (young) and 7.08 ± 0.11 (older) to 6.84 ± 0.19 (young, P < 0.05) and to 6.75 ± 0.25 (older, P < 0.05). Average values of the pseudo-first-order reaction rate k(PCr→ATP)at rest were 0.07 ± 0.04 s−1in the young and 0.07 ± 0.03 s−1in the older group. At both exercise levels, the reaction rate constant increased compared with the resting value, but only the difference between the resting value and the 20% MVC value, which showed an 86% higher reaction rate constant in both groups, reached statistical significance ( P < 0.05). No difference in the reaction rate constant between the young and older groups was observed at either exercise level. As with k(PCr→ATP), the average phosphorus flux through the CK reaction increased during exercise at 20% MVC ( P < 0.05 in the older group) but decreased toward resting values at 40% MVC in both groups. The data in our study suggest that normal aging does not significantly affect the metabolic processes associated with the CK reaction.
Palmitate oxidation rate and action on glycogen synthase in myoblasts from insulin-resistant subjects
Authors: Mott David M. , Hoyt Cristen , Caspari Rael , Stone Karen , Pratley Richard , Bogardus Clifton
Published: December 2017

Elevated plasma lipid and nonesterified fatty acid concentrations reduce insulin-mediated glucose disposal in skeletal muscle. Cultured myoblasts from 21 subjects were studied for rates of palmitate oxidation and the effect of palmitate on glycogen synthase activity at the end of an 18-h incubation in serum- and glucose-free media. Oxidation rates of 40 μM palmitate in cultured myoblasts correlated with the fasting glucose ( r = 0.71, P = 0.001), log fasting insulin ( r = 0.52, P = 0.03), and insulin-mediated glucose storage rate ( r = −0.50, P = 0.04) of the muscle donors. Myoblast glycogen synthase activity can be regulated by 240 μM palmitate, but the changes are associated with the basal respiratory quotient and not with the insulin resistance of the muscle donor. These results indicate that myoblasts producing elevated palmitate oxidation rates in vitro can be used to identify skeletal muscle abnormalities which are primary contributors to insulin resistance in vivo. Effects of 240 μM palmitate on myoblast glycogen synthase activity appear to be mechanistically different from the relationship between myoblast palmitate oxidation rates and insulin resistance of the muscle donor.
Glucagon response to exercise is critical for accelerated hepatic glutamine metabolism and nitrogen disposal
Authors: Krishna Mahesh G. , Coker Robert H. , Lacy D. Brooks , Zinker Bradley A. , Halseth Amy E. , Wasserman David H.
Published: December 2017

The aim of this study was to determine the role of glucagon in hepatic glutamine (Gln) metabolism during exercise. Sampling (artery, portal vein, and hepatic vein) and infusion (vena cava) catheters and flow probes (portal vein, hepatic artery) were implanted in anesthetized dogs. At least 16 days after surgery, an experiment, consisting of a 120-min equilibration period, a 30-min basal sampling period, and a 150-min exercise period, was performed in these animals. [5-15N]Gln was infused throughout experiments to measure gut and liver Gln kinetics and the incorporation of Gln amide nitrogen into urea. Somatostatin was infused throughout the study. Glucagon was infused at a basal rate until the beginning of exercise, when the rate was either 1) gradually increased to simulate the glucagon response to exercise ( n = 5) or 2) unchanged to maintain basal glucagon ( n = 5). Insulin was infused during the equilibration and basal periods at rates designed to achieve stable euglycemia. The insulin infusion was reduced in both protocols to simulate the exercise-induced insulin decrement. These studies show that the exercise-induced increase in glucagon is 1) essential for the increase in hepatic Gln uptake and fractional extraction, 2) required for the full increment in ureagenesis, 3) required for the specific transfer of the Gln amide nitrogen to urea, and 4) unrelated to the increase in gut fractional Gln extraction. These data show, by use of the physiological perturbation of exercise, that glucagon is a physiological regulator of hepatic Gln metabolism in vivo.
Effects of fructose on hepatic glucose metabolism in humans
Authors: Dirlewanger Mirjam , Schneiter Philippe , Jéquier Eric , Tappy Luc
Published: December 2017

Hepatic and extrahepatic insulin sensitivity was assessed in six healthy humans from the insulin infusion required to maintain an 8 mmol/l glucose concentration during hyperglycemic pancreatic clamp with or without infusion of 16.7 μmol · kg−1 · min−1fructose. Glucose rate of disappearance (GRd), net endogenous glucose production (NEGP), total glucose output (TGO), and glucose cycling (GC) were measured with [6,6-2H2]- and [2-2H1]glucose. Hepatic glycogen synthesis was estimated from uridine diphosphoglucose (UDPG) kinetics as assessed with [1-13C]galactose and acetaminophen. Fructose infusion increased insulin requirements 2.3-fold to maintain blood glucose. Fructose infusion doubled UDPG turnover, but there was no effect on TGO, GC, NEGP, or GRd under hyperglycemic pancreatic clamp protocol conditions. When insulin concentrations were matched during a second hyperglycemic pancreatic clamp protocol, fructose administration was associated with an 11.1 μmol · kg−1 · min−1increase in TGO, a 7.8 μmol · kg−1 · min−1increase in NEGP, a 2.2 μmol · kg−1 · min−1increase in GC, and a 7.2 μmol · kg−1 · min−1decrease in GRd ( P < 0.05). These results indicate that fructose infusion induces hepatic and extrahepatic insulin resistance in humans.
Growth hormone enhances effects of endurance training on oxidative muscle metabolism in elderly women
Authors: Lange Kai Henrik Wiborg , Isaksson Fredrik , Juul Anders , Rasmussen Michael Højby , Bülow Jens , Kjær Michael
Published: December 2017

The present study investigated whether recombinant human (rh) growth hormone (GH) combined with endurance training would have a larger effect on oxidative capacity, metabolism, and body fat than endurance training alone. Sixteen healthy, elderly women, aged 75 yr, performed closely monitored endurance training on a cycle ergometer over 12 wk. rhGH was given in a randomized, double-blinded, placebo-controlled design in addition to the training program. GH administration resulted in a doubling of serum insulin-like growth factor I levels. With endurance training, peak oxygen uptake increased by ∼18% in both groups, whereas the marked increase in muscle citrate synthase activity was 50% larger in the GH group compared with the placebo group. In addition, only the GH group revealed an increase in musclel-3-hydroxyacyl-CoA dehydrogenase activity. Body weight remained unchanged in both groups, but the GH group showed significant changes in body composition with a decrease in fat mass and an increase in lean body mass. Twenty-four-hour indirect calorimetry performed in four subjects showed a marked increase in energy expenditure with increased relative and absolute fat combustion in the two subjects receiving rhGH. In conclusion, rhGH adds to the effects of endurance training on muscle oxidative enzymes and causes a reduction in body fat in elderly women.
Increasing membrane-bound MCSF does not enhance OPGL-driven osteoclastogenesis from marrow cells
Authors: Fan X. , Fan D. , Gewant H. , Royce C. L. , Nanes M. S. , Rubin J.
Published: December 2017

Macrophage colony-stimulating factor (MCSF) and osteoprotegerin ligand (OPGL), both produced by osteoblasts/stromal cells, are essential factors for osteoclastogenesis. Whether local MCSF levels regulate the amount of osteoclast formation is unclear. Two culture systems, ST-2 and Chinese hamster ovary-membrane-bound MCSF (CHO-mMCSF)-Tet-OFF cells, were used to study the role of mMCSF in osteoclast formation. Cells from bone marrow (BMM) or spleen were cultured with soluble OPGL on glutaraldehyde-fixed cell layers; osteoclasts formed after 7 days. Osteoclast number was proportional to the amount of soluble OPGL added. In contrast, varying mMCSF levels in the ST-2 or CHO-mMCSF-Tet-OFF cell layers, respectively by variable plating or by addition of doxycycline, did not affect BMM osteoclastogenesis: 20–450 U of mMCSF per well generated similar osteoclast numbers. In contrast, spleen cells were resistant to mMCSF: osteoclastogenesis required ≥250 U per well and further increased as mMCSF rose higher. Our results demonstrate that osteoclast formation in the local bone environment is dominated by OPGL. Increasing mMCSF above basal levels does not further enhance osteoclast formation from BMMs, indicating that mMCSF does not play a dominant regulatory role in the bone marrow.
β-Adrenoceptor-mediated thermogenesis and lipolysis in patients with chronic obstructive pulmonary disease
Authors: Schiffelers S. L. H. , Blaak E. E. , Baarends E. M. , Van Baak M. A. , Saris W. H. M. , Wouters E. F. M. , Schols A. M. W. J.
Published: December 2017

The present study investigated whether development or maintenance of a relatively increased fat mass in normal-weight patients with chronic obstructive pulmonary disease (COPD), despite periods of weight loss, may be related to impaired β-adrenoceptor-mediated responses in lipid utilization and thermogenesis. Nine COPD patients and nine healthy controls (body mass index: 23.0 ± 1.3 vs. 23.8 ± 0.6 kg/m2, not significant; fat mass: 19.0 ± 2.1 vs. 11.9 ± 1.5 kg, P < 0.01) received consecutive 30-min infusions of 6, 12, and 24 ng · kg fat free mass−1 · min−1 isoproterenol. During β-adrenergic stimulation, nonesterified fatty acid levels increased significantly less in COPD patients ( P < 0.001). Respiratory exchange ratio decreased similarly in both groups, indicating a similar change in the rate of lipid to carbohydrate oxidation. Energy expenditure increased similarly in both groups during β-adrenergic stimulation. However, because plasma isoproterenol concentrations were significantly higher in COPD patients, thermogenesis related to isoproterenol concentration was significantly reduced in this group ( P < 0.05). In conclusion, β-adrenoceptor-mediated lipolysis and thermogenesis are impaired in COPD patients. This may play a role in the development or maintenance of their relatively increased fat mass.
Estrogen enhances mechanical stress-induced prostaglandin production by bone cells from elderly women
Authors: Joldersma Manon , Klein-Nulend Jenneke , Oleksik Anna M. , Heyligers Ide C. , Burger Elisabeth H.
Published: December 2017

Several studies indicate that estrogen may enhance the effects of mechanical loading on bone mineral density in elderly women. This stimulating effect of estrogen could be due to increased sensitivity of bone cells to mechanical stress in the presence of estrogen. The present study was performed to determine whether 17β-estradiol (E2) enhances mechanical stress-induced prostaglandin production and cyclooxygenase (COX)-2 mRNA expression. We subjected bone cells from seven nonosteoporotic women between 56 and 75 yr of age for 1 h to pulsating fluid flow (PFF) in the presence or absence of 10−11M E2and measured prostaglandin production and COX-1 and COX-2 mRNA expression. One hour of PFF stimulated prostaglandin (PG)E2production threefold, PGI2production twofold, and COX-2, but not COX-1, mRNA expression 2.9-fold. Addition of E2further enhanced PFF-stimulated PGE2production by 1.9-fold but did not significantly affect PGI2production or COX-2 or COX-1 mRNA expression. E2by itself did not affect any of the parameters measured. These results suggest that estrogen modulates bone cell mechanosensitivity via the prostaglandin synthetic pathway independently of COX mRNA expression.
Autoregulation of glucose production in men with a glycerol load during rest and exercise
Authors: Trimmer Jeff K. , Casazza Gretchen A. , Horning Michael A. , Brooks George A.
Published: December 2017

Related to hepatic autoregulation we evaluated hypotheses that 1) glucose production would be altered as a result of a glycerol load, 2) decreased glucose recycling rate (Rr) would result from increased glycerol uptake, and 3) the absolute rate of gluconeogenesis (GNG) from glycerol would be positively correlated to glycerol rate of disappearance (Rd) during a glycerol load. For these purposes, glucose and glycerol kinetics were determined in eight men during rest and during 90 min of leg cycle ergometry at 45 and 65% of peak O2consumption (V˙o2 peak). Trials were conducted after an overnight fast, with exercise commencing 12 h after the last meal. Subjects received a continuous infusion of [6,6-2H2]glucose, [1-13C]glucose, and [1,1,2,3,3-2H5]glycerol without (CON) or with an additional 1,000 mg (rest: 20 mg/min; exercise: 40 mg/min) of [2-13C]- or unlabeled glycerol added to the infusate (GLY). Infusion of glycerol dampened glucose Rr, calculated as the difference between [6,6-2H2]- and [1-13C]glucose rates of appearance (Ra), at rest [0.35 ± 0.12 (CON) vs. 0.12 ± 0.10 mg · kg−1· min−1(GLY), P < 0.05] and during exercise at both intensities [45%: 0.63 ± 0.14 (CON) vs. 0.04 ± 0.12 (GLY); 65%: 0.73 ± 0.14 (CON) vs. 0.04 ± 0.17 mg · kg−1· min−1(GLY), P < 0.05]. Glucose Raand oxidation were not affected by glycerol infusion at rest or during exercise. Throughout rest and both exercise intensities, glycerol Rdwas greater in GLY vs. CON conditions (rest: 0.30 ± 0.04 vs. 0.58 ± 0.04; 45%: 0.57 ± 0.07 vs. 1.19 ± 0.04; 65%: 0.73 ± 0.06 vs. 1.27 ± 0.05 mg · kg−1· min−1, CON vs. GLY, respectively). Differences in glycerol Rd(ΔRd) between protocols equaled the unlabeled glycerol infusion rate and correlated with plasma glycerol concentration ( r = 0.97). We conclude that infusion of a glycerol load during rest and exercise at 45 and 65% ofV˙o2 peak1) does not affect glucose Raor Rd, 2) blocks glucose Rr, 3) increases whole body glycerol Rdin a dose-dependent manner, and 4) results in gluconeogenic rates from glycerol equivalent to CON glucose recycling rates.
T3 increases mitochondrial ATP production in oxidative muscle despite increased expression of UCP2 and -3
Authors: Short Kevin R. , Nygren Jonas , Barazzoni Rocco , Levine James , Nair K. Sreekumaran
Published: December 2017

Triiodothyronine (T3) increases O2 and nutrient flux through mitochondria (Mito) of many tissues, but it is unclear whether ATP synthesis is increased, particularly in different types of skeletal muscle, because variable changes in uncoupling proteins (UCP) and enzymes have been reported. Thus Mito ATP production was measured in oxidative and glycolytic muscles, as well as in liver and heart, in rats administered T3 for 14 days. Relative to saline-treated controls, T3 rats had 80, 168, and 62% higher ATP production in soleus muscle, liver, and heart, respectively, as well as higher activities of citrate synthase (CS; 63, 90, 25%) and cytochrome c oxidase (COX; 119, 225, 52%) in the same tissues (all P < 0.01). In plantaris muscle of T3 rats, CS was only slightly higher (17%, P < 0.05) than in controls, and ATP production and COX were unaffected. mRNA levels of COX I and III were 33 and 47% higher in soleus of T3 rats ( P < 0.01), but there were no differences in plantaris. In contrast, UCP2 and -3 mRNAs were 2.5- to 14-fold higher, and protein levels were 3- to 10-fold higher in both plantaris and soleus of the T3 group. We conclude that T3 increases oxidative enzymes and Mito ATP production and Mito-encoded transcripts in oxidative but not glycolytic rodent tissues. Despite large increases in UCP expression, ATP production was enhanced in oxidative tissues and maintained in glycolytic muscle of hyperthyroid rats.
Functional limitations to glucose uptake in muscles comprised of different fiber types
Authors: Halseth Amy E. , Bracy Deanna P. , Wasserman David H.
Published: December 2017

Skeletal muscle glucose uptake requires delivery of glucose to the sarcolemma, transport across the sarcolemma, and the irreversible phosphorylation of glucose by hexokinase (HK) inside the cell. Here, a novel method was used in the conscious rat to address the roles of these three steps in controlling the rate of glucose uptake in soleus, a muscle comprised of type I fibers, and two muscles comprised of type II fibers. Experiments were performed on conscious rats under basal conditions or during hyperinsulinemic euglycemic clamps. Rats received primed, constant infusions of 3- O-methyl-[3H]glucose (3- O-MG) and [1-14C]mannitol. Total muscle glucose concentration and the steady-state ratio of intracellular to extracellular 3- O-MG concentration, which distributes based on the transsarcolemmal glucose gradient (TSGG), were used to calculate glucose concentrations at the inner and outer sarcolemmal surfaces ([G]imand [G]om, respectively) in muscle. Muscle glucose uptake was much lower in muscle comprised of type II fibers than in soleus under both basal and insulin-stimulated conditions. Under all conditions, the TSGG in type II muscle exceeded that in soleus, indicating that glucose transport plays a more important role to limit glucose uptake in type II muscle. Although hyperinsulinemia increased [G]imin soleus, indicating that phosphorylation was a limiting factor, type II muscle was limited primarily by glucose delivery and glucose transport. In conclusion, the relative importance of glucose delivery, transport, and phosphorylation in controlling the rate of insulin-stimulated muscle glucose uptake varies between muscle fiber types, with glucose delivery and transport being the primary limiting factors in type II muscle.
Magnitude and variation of ratio of total body potassium to fat-free mass: a cellular level modeling study
Authors: Wang Zimian , Pi-Sunyer F. Xavier , Kotler Donald P. , Wang Jack , Pierson Richard N. , Heymsfield Steven B.
Published: December 2017

Potassium is an essential element of living organisms that is found almost exclusively in the intracellular fluid compartment. The assumed constant ratio of total body potassium (TBK) to fat-free mass (FFM) is a cornerstone of the TBK method of estimating total body fat. Although the TBK-to-FFM (TBK/FFM) ratio has been assumed constant, a large range of individual and group values is recognized. The purpose of the present study was to undertake a comprehensive analysis of biological factors that cause variation in the TBK/FFM ratio. A theoretical TBK/FFM model was developed on the cellular body composition level. This physiological model includes six factors that combine to produce the observed TBK/FFM ratio. The ratio magnitude and range, as well as the differences in the TBK/FFM ratio between men and women and variation with growth, were examined with the proposed model. The ratio of extracellular water to intracellular water ( E/I) is the major factor leading to between-individual variation in the TBK/FFM ratio. The present study provides a conceptual framework for examining the separate TBK/FFM determinants and suggests important limitations of the TBK/FFM method used in estimating total body fat in humans and other mammals.
Parathyroid cells express dihydropyridine-sensitive cation currents and L-type calcium channel subunits
Authors: Chang Wenhan , Pratt Stacy A. , Chen Tsui-Hua , Tu Chia-Ling , Mikala Gabor , Schwartz Arnold , Shoback Dolores
Published: December 2017

Parathyroid cells express Ca2+-conducting currents that are activated by raising the extracellular Ca2+concentration ([Ca2+]o). We investigated the sensitivity of these currents to dihydropyridines, the expression of voltage-dependent Ca2+channel (VDCC) subunits, and the effects of dihydropyridines on the intracellular free [Ca2+] ([Ca2+]i) and secretion in these cells. Dihydropyridine channel antagonists dose dependently suppressed Ca2+-conducting currents, and agonists partially reversed the inhibitory effects of the antagonists in these cells. From a bovine parathyroid cDNA library, we isolated cDNA fragments encoding parts of an α1S- and a β3-subunit of L-type Ca2+channels. The α1S-subunit cDNA from the parathyroid represents an alternatively spliced variant lacking exon 29 of the corresponding gene. Northern blot analysis and immunocytochemistry confirmed the presence of transcripts and proteins for α1- and β3-subunits in the parathyroid gland. The addition of dihydropyridines had no significant effects on high [Ca2+]o-induced changes in [Ca2+]iand parathyroid hormone (PTH) release. Thus our studies indicate that parathyroid cells express alternatively spliced L-type Ca2+channel subunits, which do not modulate acute intracellular Ca2+responses or changes in PTH release.
GLP-1-induced alterations in the glucose-stimulated insulin secretory dose-response curve
Authors: Brandt Andreas , Katschinski Martin , Arnold Rudolf , Polonsky Kenneth S. , Göke Burkhard , Byrne Maria M.
Published: December 2017

The present study was undertaken to establish in normal volunteers the alterations in β-cell responsiveness to glucose associated with a constant infusion of glucagon-like peptide-1 (GLP-1) or a pretreatment infusion for 60 min. A high-dose graded glucose infusion protocol was used to explore the dose-response relationship between glucose and insulin secretion. Studies were performed in 10 normal volunteers, and insulin secretion rates (ISR) were calculated by deconvolution of peripheral C-peptide levels by use of a two-compartmental model that utilized mean kinetic parameters. During the saline study, from 5 to 15 mM glucose, the relationship between glucose and ISR was linear. Constant GLP-1 infusion (0.4 pmol · kg−1· min−1) shifted the dose-response curve to the left, with an increase in the slope of this curve from 5 to 9 mM glucose from 71.0 ± 12.4 pmol · min−1· mM−1during the saline study to 241.7 ± 36.6 pmol · min−1· mM−1during the constant GLP-1 infusion ( P < 0.0001). GLP-1 consistently stimulated a >200% increase in ISR at each 1 mM glucose interval, maintaining plasma glucose at <10 mM ( P < 0.0007). Pretreatment with GLP-1 for 60 min resulted in no significant priming of the β-cell response to glucose ( P = 0.2). Insulin clearance rates were similar in all three studies at corresponding insulin levels. These studies demonstrate that physiological levels of GLP-1 stimulate glucose-induced insulin secretion in a linear manner, with a consistent increase in ISR at each 1 mM glucose interval, and that they have no independent effect on insulin clearance and no priming effect on subsequent insulin secretory response to glucose.
IGF-binding protein-5 stimulates osteoblast activity and bone accretion in ovariectomized mice
Authors: Andress Dennis L.
Published: December 2017

Insulin-like growth factor binding protein-5 (IGFBP-5) is an osteoblast secretory protein that becomes incorporated into the mineralized bone matrix. In osteoblast cultures, IGFBP-5 stimulates cell proliferation by an IGF-independent mechanism. To evaluate whether IGFBP-5 can stimulate osteoblast activity and enhance bone accretion in a mouse model of osteoblast insufficiency, daily subcutaneous injections of either intact [IGFBP-5 (intact)] or carboxy-truncated IGFBP-5 [IGFBP-5-(1–169)] were given to ovariectomized (OVX) mice for 8 wk. Femur and spine bone mineral density (BMD), measured every 2 wk, showed early and sustained increases in response to IGFBP-5. Bone histomorphometry of cancellous bone showed significant elevations in the bone formation rate in both the femur metaphysis [IGFBP-5- (1)] only) and spine compared with OVX controls. IGFBP-5 also stimulated osteoblast number in the femur IGFBP-5-(1–169) only) and spine. These data indicate that IGFBP-5 effectively enhances bone formation and bone accretion in OVX mice by stimulating osteoblast activity. The finding that IGFBP-5-(1–169) is bioactive in vivo indicates that the carboxy-terminal portion is not required for this bone anabolic effect.
Prenatal cytokine exposure results in obesity and gender-specific programming
Authors: Dahlgren Jovanna , Nilsson Cecilia , Jennische Eva , Ho Hoi-Por , Eriksson Elias , Niklasson Aimon , Björntorp Per , Wikland Kerstin Albertsson , Holmäng Agneta
Published: December 2017

Prenatal events appear to program hormonal homeostasis, contributing to the development of somatic disorders at an adult age. The aim of this study was to examine whether maternal exposure to cytokines or to dexamethasone (Dxm) would be followed by hormonal consequences in the offspring at adult age. Pregnant rats were injected on days 8, 10, and 12 of gestation with either human interleukin-6 (IL-6) or tumor necrosis factor-α (TNF-α) or with Dxm. Control dams were injected with vehicle. All exposed offspring developed increased body weight ( P < 0.05–0.001), apparently due to an increase of 30–40% in adipose tissue weight ( P < 0.05–0.01). Corticosterone response to stress was increased in the IL-6 group ( P < 0.05–0.01). Dxm-treated male rats exhibited blunted Dexamethasone suppression test results. In male rats, insulin sensitivity was decreased after IL-6 exposure ( P < 0.01), whereas basal insulin was elevated in the TNF-α group ( P < 0.01). In female rats, plasma testosterone levels were higher in all exposed groups compared with controls ( P < 0.01–0.001), with the exception of Dxm-exposed offspring. Males in the TNF-α group showed decreased locomotor activity ( P < 0.05), and females in the IL-6 group showed increased locomotor activity ( P < 0.05). These results indicate that prenatal exposure to cytokines or Dxm leads to increased fat depots in both genders. In females, cytokine exposure was followed by a state of hyperandrogenicity. The results suggest that prenatal exposure to cytokines or Dxm can induce gender-specific programming of neuroendocrine regulation with consequences in adult life.
Regulation of fatty acid oxidation and glucose metabolism in rat soleus muscle: effects of AICAR
Authors: Kaushik Virendar K. , Young Martin E. , Dean David J. , Kurowski Theodore G. , Saha Asish K. , Ruderman Neil B.
Published: December 2017

Previous studies have shown that 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a cell-permeable activator of AMP-activated protein kinase, increases the rate of fatty acid oxidation in skeletal muscle of fed rats. The present study investigated the mechanism by which this occurs and, in particular, whether changes in the activity of malonyl-CoA decarboxylase (MCD) and the β-isoform of acetyl-CoA carboxylase (ACCβ) are involved. In addition, the relationship between changes in fatty acid oxidation induced by AICAR and its effects on glucose uptake and metabolism was examined. In incubated soleus muscles isolated from fed rats, AICAR (2 mM) increased fatty acid oxidation (90%) and decreased ACCβ activity (40%) and malonyl-CoA concentration (50%); however, MCD activity was not significantly altered. In soleus muscles from overnight-fasted rats, AICAR decreased ACCβ activity (40%), as it did in fed rats; however, it had no effect on the already high rate of fatty acid oxidation or the low malonyl-CoA concentration. In keeping with its effect on fatty acid oxidation, AICAR decreased glucose oxidation by 44% in fed rats but did not decrease glucose oxidation in fasted rats. It had no effect on glucose oxidation when fatty acid oxidation was inhibited by 2-bromopalmitate. Surprisingly, AICAR did not significantly increase glucose uptake or assayable AMP-activated protein kinase activity in incubated soleus muscles from fed or fasted rats. These results indicate that, in incubated rat soleus muscle, 1) AICAR does not activate MCD or stimulate glucose uptake as it does in extensor digitorum longus and epitrochlearis muscles, 2) the ability of AICAR to increase fatty acid oxidation and diminish glucose oxidation and malonyl-CoA concentration is dependent on the nutritional status of the rat, and 3) the ability of AICAR to diminish assayable ACC activity is independent of nutritional state.
Methods for measuring glycogen cycling
Authors: Landau Bernard R.
Published: December 2017

Simultaneous synthesis and breakdown of glycogen is called glycogen cycling. The extent of hyperglycemia and decreased glycogen stores in diabetes mellitus may relate in part to the extent cycling occurs. Four methods have been introduced to estimate its extent in liver in humans. 1) In the fasted state, the rate of net hepatic glycogenolysis, i.e., glycogen breakdown minus synthesis, is estimated using NMR, and the rate of glycogenolysis is estimated from deuterium labeling of blood glucose on2H2O ingestion. 2) The rate of glycogen synthesis is estimated from the rate of labeling of carbon 1 of glycogen on [1-13C]glucose infusion, monitored by NMR, and the rate of breakdown from the rate of disappearance of that labeling on unlabeled glucose infusion. 3) The rate of synthesis from glucose-1- P, formed by glycogenolysis, is measured by the decrease in the3H/14C ratio in acetaminophen glucuronide on acetaminophen and [2-3H,6-14C]galactose administration. 4) The rate of synthesis is estimated from the dilution of label from labeled galactose in its conversion to the acetaminophen glucuronide, and the rate of glycogenolysis is estimated from the amount of label in blood glucose. In the first method, the fate of glucose-6- P is assumed to be only to glycogen and glucose. In the second, only glucose-6- P molecules formed by breakdown that are not cycled back to glycogen are measured. In the third,3H is assumed to be removed completely during cycling, and only the molecules cycled back to glycogen are measured. In the fourth, galactose conversion to glucose is assumed to be via glycogen. Quantitations in all four methods depend on assuming the order in which the molecules deposited in glycogen are released.
Catecholamines inhibit Ca2+-dependent proteolysis in rat skeletal muscle through β2-adrenoceptors and cAMP
Authors: Navegantes Luiz Carlos C. , Resano Neusa M. Z. , Migliorini Renato H. , Kettelhut Ísis C.
Published: December 2017

Overall proteolysis and the activity of skeletal muscle proteolytic systems were investigated in rats 1, 2, or 4 days after adrenodemedullation. Adrenodemedullation reduced plasma epinephrine by 95% and norepinephrine by 35% but did not affect muscle norepinephrine content. In soleus and extensor digitorum longus (EDL) muscles, rates of overall proteolysis increased by 15–20% by 2 days after surgery but returned to normal levels after 4 days. The rise in rates of protein degradation was accompanied by an increased activity of Ca2+-dependent proteolysis in both muscles, with no significant change in the activity of lysosomal and ATP-dependent proteolytic systems. In vitro rates of Ca2+-dependent proteolysis in soleus and EDL from normal rats decreased by ∼35% in the presence of either 10−5M clenbuterol, a β2-adrenergic agonist, or epinephrine or norepinephrine. In the presence of dibutyryl cAMP, proteolysis was reduced by 62% in soleus and 34% in EDL. The data suggest that catecholamines secreted by the adrenal medulla exert an inhibitory control of Ca2+-dependent proteolysis in rat skeletal muscle, mediated by β2-adrenoceptors, with the participation of a cAMP-dependent pathway.
Evidence of separate pathways for lactate uptake and release by the perfused rat heart
Authors: Chatham John C. , Des Rosiers Christine , Forder John R.
Published: December 2017

The simultaneous release and uptake of lactate by the heart has been observed both in vivo and ex vivo; however, the pathways underlying these observations have not been satisfactorily explained. Consequently, the purpose of this study was to test the hypothesis that hearts release lactate from glycolysis while simultaneously taking up exogenous lactate. Therefore, we determined the effects of fatty acids and diabetes on the regulation of lactate uptake and release. Hearts from control and 1-wk diabetic animals were perfused with 5 mM glucose, 0.5 mM [3-13C]lactate, and 0, 0.1, 0.32, or 1.0 mM palmitate. Parameters measured include perfusate lactate concentrations, fractional enrichment, and coronary flow rates, which enabled the simultaneous, but independent, measurements of the rates of 1) uptake of exogenous [13C]lactate and 2) efflux of unlabeled lactate from metabolism of glucose. Although the rates of lactate uptake and efflux were both similarly inhibited by the addition of palmitate, (i.e., the ratio of lactate uptake to efflux remained constant), the ratio of lactate uptake to efflux was significantly higher in the controls compared with the diabetic group (1.00 ± 0.14 vs. 0.50 ± 0.07, P < 0.002). These data, combined with heterogeneous13C enrichment of tissue lactate, pyruvate, and alanine, suggest that glycolytically derived lactate production and oxidation of exogenous lactate operate as functionally separate metabolic pathways. These results are consistent with the concept of an intracellular lactate shuttle.
Characteristics of circulating growth hormone in women after acute heavy resistance exercise
Authors: Hymer Wesley C. , Kraemer William J. , Nindl Bradley C. , Marx James O. , Benson David E. , Welsch Jill R. , Mazzetti Scott A. , Volek Jeff S. , Deaver Daniel R.
Published: December 2017

The effects of exercise on the molecular nature of secreted human growth hormone (GH) or its biological activity are not well understood. Plasma from women (average age 23.6 yr, n = 35), drawn before and after an acute heavy resistance exercise test, was fractionated by size exclusion chromatography into three size classes, namely, >60 kDa ( fraction A), 30–60 kDa ( fraction B), and <30 kDa ( fraction C), before GH assay. Concentrations of GH in these fractions, as well as in unfractioned plasma, were measured by the Nichols immunoradiometric assay, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) polyclonal competitive RIA, Diagnostic Systems Laboratory's immunofunctional assay (measures dimerization-capable species), and the rat tibial bioassay. Significantly increased circulating GH concentrations of two- to fourfold were observed when immunoassays in unfractionated plasma samples were used, but they showed no significant change with use of the rat tibial bioassay. Significant exercise-induced increases in GH were found in fractions B and C but not in fraction A. Because chemical reduction of the samples before GH immunoassay significantly increased GH concentrations in fractions B and C (Nichols and NIDDK kits) after exercise, it is concluded that exercise may specifically increase release of disulfide-linked hormone molecules and/or fragments. Finally, because most of the GH released after exercise was able to dimerize the GH receptor in vitro, it is also concluded that these forms have the two intact binding sites required to initiate signal transduction in target cells.
Normal Akt/PKB with reduced PI3K activation in insulin-resistant mice
Authors: Nadler Samuel T. , Stoehr Jonathan P. , Rabaglia Mary E. , Schueler Kathryn L. , Birnbaum Morris J. , Attie Alan D.
Published: December 2017

Insulin stimulates muscle and adipose tissue to absorb glucose through a signaling cascade that is incompletely understood. Insulin resistance, the inability of insulin to appropriately stimulate glucose uptake, is a hallmark of type 2 diabetes mellitus. The development of experimental systems that model human insulin resistance is important in elucidating the defects responsible for the development of type 2 diabetes. When two strains of mice, BTBR and C57BL/6J (B6), are crossed, the resultant male offspring (BtB6) demonstrate insulin resistance in muscle tissue. Here, we report an insulin resistance phenotype in adipose tissue from lean, nondiabetic BtB6 mice similar to that observed in human muscle. Adipocytes isolated from insulin-resistant male mice display 65% less insulin-stimulated glucose uptake compared with insulin-sensitive female mice. Similarly, adipocytes from insulin-resistant mice have diminished insulin-stimulated IRS-1 phosphorylation and phosphatidylinositol 3-kinase (PI3K) activation. However, normal activation of protein kinase B (Akt/PKB) by insulin is observed. Thus BtB6 mice demonstrate the dissociation of insulin-stimulated PI3K activity and Akt/PKB activation and represent a useful model to investigate the causes of insulin resistance in humans.
Impaired sarcolemmal vesicle lactate uptake and skeletal muscle MCT1 and MCT4 expression in obese Zucker rats
Authors: Py Guillaume , Lambert Karen , Perez-Martin Antonia , Raynaud Eric , Préfaut Christian , Mercier Jacques
Published: December 2017

The present experiments were undertaken to characterize 1) the hindlimb muscle mass lactate uptake and 2) the expression of monocarboxylate transporter isoforms MCT1 and MCT4, as well as lactate dehydrogenase (LDH) isozyme distribution, in various skeletal muscles of Zucker fa/fa rats taken as a model of insulin resistance-related obesity. Initial lactate uptake at six different concentrations was measured in sarcolemmal vesicles (SV) by use ofl-[U-14C]lactate. Compared with controls, the maximal rate of lactate uptake and affinity were decreased in SV of Zucker rats (∼30%) in which MCT4 content was significantly decreased ( P < 0.05). MCT4 expression was decreased in soleus, extensor digitorum longus, and red tibialis anterior (RTA; P < 0.05), but not in white tibialis anterior, whereas MCT1 expression was decreased only in RTA of Zucker rats ( P < 0.05). Obesity led to a shift toward type M-LDH isozyme in mixed muscles. We conclude that obesity leads to changes in muscular MCT1 and MCT4 expression, which, when associated with LDH isozyme redistribution, may contribute to the hyperlactatemia noted in insulin resistance.
Increasing fructose 2,6-bisphosphate overcomes hepatic insulin resistance of type 2 diabetes
Authors: Wu Chaodong , Okar David A. , Newgard Christopher B. , Lange Alex J.
Published: December 2017

Hepatic glucose production is increased as a metabolic consequence of insulin resistance in type 2 diabetes. Because fructose 2,6-bisphosphate is an important regulator of hepatic glucose production, we used adenovirus-mediated enzyme overexpression to increase hepatic fructose 2,6-bisphosphate to determine if the hyperglycemia in KK mice, polygenic models of type 2 diabetes, could be ameliorated by reduction of hepatic glucose production. Seven days after treatment with virus encoding a mutant 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase designed to increase fructose 2,6-bisphosphate levels, plasma glucose, lipids, and insulin were significantly reduced in KK/H1J and KK.Cg-Ay/J mice. Moreover, high fructose 2,6-bisphosphate levels downregulated glucose-6-phosphatase and upregulated glucokinase gene expression, thereby reversing the insulin-resistant pattern of hepatic gene expression of these two key glucose-metabolic enzymes. The increased hepatic fructose 2,6-bisphosphate also reduced adiposity in both KK mice. These results clearly indicate that increasing hepatic fructose 2,6-bisphosphate overcomes the impairment of insulin in suppressing hepatic glucose production, and it provides a potential therapy for type 2 diabetes.
MCP-1 but not CINC synthesis is increased in rat pancreatic acini in response to cerulein hyperstimulation
Authors: Bhatia Madhav , Brady Mark , Kang Yun Kyung , Costello Eithne , Newton Darren J. , Christmas Stephen E. , Neoptolemos John P. , Slavin John
Published: December 2017

Inflammatory mediators including chemokines play a critical role in acute pancreatitis. The precise nature of early inflammatory signals within the pancreas remains, however, unclear. We examined the ability of isolated pancreatic acini to synthesize CC chemokine monocyte chemotactic protein-1 (MCP-1) and CXC chemokine cytokine-induced neutrophil chemoattractant (CINC) and the response to the secretagogue cerulein at physiological and supraphysiological concentrations. Isolated rat pancreatic acini maintained in short-term (≤48 h) primary culture constitutively synthesized MCP-1 and CINC. Cerulein (10−7M; supramaximal dose) increased production of MCP-1 but not CINC. Cerulein-induced increase in MCP-1 synthesis was accompanied by increase in nuclear factor (NF)-κB activation shown by EMSA. Pretreatment with NF-κB inhibitors N-acetylcysteine (NAC) and N-tosylphenyalanine chloromethyl ketone (TPCK) blocked cerulein-induced NF-κB activation and abolished cerulein's effect on MCP-1 synthesis. Pretreatment with calcium antagonist BAPTA-AM also blocked cerulein's effect on MCP-1 synthesis. These results indicate that isolated acini synthesize MCP-1 and CINC and support the idea of acinar-derived chemokines as early mediators of inflammatory response in acute pancreatitis. Although cerulein hyperstimulation increased MCP-1 synthesis by a calcium-dependent mechanism involving NF-κB activation, CINC synthesis was not affected. This suggests that regulation of CC and CXC chemokines within acinar cells may be quite different.