bluuebunny/crossref_metadata_2025 huggingface dataset:
Progressive increase in human skeletal muscle AMPKα2 activity and ACC phosphorylation during exercise
Authors: Stephens T. J. , Chen Z.-P. , Canny B. J. , Michell B. J. , Kemp B. E. , McConell G. K.
Published: February 2015

The effect of prolonged moderate-intensity exercise on human skeletal muscle AMP-activated protein kinase (AMPK)α1 and -α2 activity and acetyl-CoA carboxylase (ACCβ) and neuronal nitric oxide synthase (nNOSμ) phosphorylation was investigated. Seven active healthy individuals cycled for 30 min at a workload requiring 62.8 ± 1.3% of peak O2consumption (V˙o2 peak) with muscle biopsies obtained from the vastus lateralis at rest and at 5 and 30 min of exercise. AMPKα1 activity was not altered by exercise; however, AMPKα2 activity was significantly ( P < 0.05) elevated after 5 min (∼2-fold), and further elevated ( P < 0.05) after 30 min (∼3-fold) of exercise. ACCβ phosphorylation was increased ( P < 0.05) after 5 min (∼18-fold compared with rest) and increased ( P< 0.05) further after 30 min of exercise (∼36-fold compared with rest). Increases in AMPKα2 activity were significantly correlated with both increases in ACCβ phosphorylation and reductions in muscle glycogen content. Fat oxidation tended ( P = 0.058) to increase progressively during exercise. Muscle creatine phosphate was lower ( P < 0.05), and muscle creatine, calculated free AMP, and free AMP-to-ATP ratio were higher ( P < 0.05) at both 5 and 30 min of exercise compared with those at rest. At 30 min of exercise, the values of these metabolites were not significantly different from those at 5 min of exercise. Phosphorylation of nNOSμ was variable, and despite the mean doubling with exercise, statistically significance was not achieved ( P = 0.304). Western blots indicated that AMPKα2 was associated with both nNOSμ and ACCβ consistent with them both being substrates of AMPKα2 in vivo. In conclusion, AMPKα2 activity and ACCβ phosphorylation increase progressively during moderate exercise at ∼60% of V˙o2 peakin humans, with these responses more closely coupled to muscle glycogen content than muscle AMP/ATP ratio.
Pronatriuretic peptide is a sensitive marker of the endocrine function of teleost heart
Authors: Vierimaa Heidi , Hirvinen Minna , Tervonen Virpi , Arjamaa Olli , Ruskoaho Heikki , Vuolteenaho Olli
Published: February 2015

We recently characterized a novel heart-specific hormone from salmon (salmon cardiac peptide, sCP). We have now prepared a recombinant plasmid expressing the NH2-terminal fragment of pro-sCP (NT-pro-sCP) and used it to set up a specific RIA for the peptide. Because of the sensitivity of the assay and the high circulating levels, NT-pro-sCP can be measured from as little as 2 μl of serum. This enables repeated sampling from the same animal in different experimental setups. Mechanical load increased the release of NT-pro-sCP from isolated perfused salmon ventricle, in parallel with sCP. Bolus injection of human endothelin-1 (ET-1; 1 μg) in the dorsal aorta of salmon resulted in an extensive increase of serum NT-pro-sCP (from 0.99 ± 0.11 to 4.6 ± 1.5 nmol/l). The response was abolished by pretreatment with a specific type A ET (ETA) receptor antagonist (BQ-123) but not with a type B ET receptor antagonist (BQ-788).The NT-pro-sCP levels had a good correlation with those of sCP ( r2= 0.75). Our results demonstrate the practical usefulness of circulating NT-pro-sCP as a marker of the endocrine function of salmon heart. They also suggest that ET-1 has an important role in regulating sCP release from teleost heart by an ETAreceptor-mediated mechanism.
Tumor necrosis factor mediates hepatic growth hormone resistance during sepsis
Authors: Yumet Gladys , Shumate Margaret L. , Bryant Patrick , Lin Cheng-Mao , Lang Charles H. , Cooney Robert N.
Published: February 2015

During sepsis, growth hormone (GH) resistance contributes to the catabolism of muscle protein. To determine the role of tumor necrosis factor (TNF) as a mediator of GH resistance, we examined the effects of a TNF antagonist [TNF-binding protein (TNFbp)] on the GH/insulin-like growth factor (IGF) I system during abdominal sepsis. To investigate potential mechanisms, the effects of TNF on the IGF-I response to GH and GH signaling were examined in cultured rat hepatocytes (CWSV-1). Three groups of rats were studied: Control, Sepsis, and Sepsis + TNFbp. Liver, gastrocnemius, and plasma were collected on day 5. In gastrocnemius, neither sepsis nor TNFbp altered the abundance of IGF-I mRNA. However, septic rats demonstrated an increase in circulating GH and a reduction in plasma IGF-I concentrations that was ameliorated by pretreatment with TNFbp. Liver from septic rats demonstrated a 50% reduction in GH receptor (GHR) and IGF-I mRNA on day 5 that was attenuated by TNFbp. However, the abundance of GHR protein was not different in liver from Control, Sepsis, or Sepsis + TNFbp rats. Consequently, a decreased amount of hepatic GHR does not explain the GH-resistant septic state. In CWSV-1 hepatocytes, TNF-α had no effect on GHR protein level but inhibited the induction of IGF-I mRNA by GH. Nuclear protein from TNF-treated hepatocytes demonstrated similar levels of phosphorylated signal transducer and activator of transcription-5 (STAT5) and DNA binding relative to controls 5 min after GH treatment. However, both of these parameters were decreased (vs. control) in TNF-treated cells 60 min after GH treatment. Collectively, these results suggest that TNF mediates hepatic GH resistance during sepsis by inhibiting the duration of signaling via the janus kinase-2/STAT5 pathway.
New bioimpedance model accurately predicts lower limb muscle volume: validation by magnetic resonance imaging
Authors: Salinari S. , Bertuzzi A. , Mingrone G. , Capristo E. , Pietrobelli A. , Campioni P. , Greco A. V. , Heymsfield S. B.
Published: February 2015

Conventional bioimpedance analysis (BIA) methods now simplify the representation of lower limb geometry and electrical properties for body composition estimation. In the present study, a three-dimensional model of the lower limb was assembled by segmentation of magnetic resonance cross-sectional images (MRI) for adipose tissue, skeletal muscle, and bone. An electrical network was then associated with this model. BIA and MRI measurements were made in six lean subjects (3 men and 3 women, age 32.2 ± 6.9 yr). Assuming 0.85 S/m for the longitudinal conductivity of the muscle, the model predicted in the examined subjects an impedance profile that conformed well to the BIA impedance profile; predicted and measured resistances were similar (261.3 ± 7.7 vs. 249 ± 9 Ω; P = not significant). The resistance profile provided, through a simpler model, muscle area estimates along the lower limb and total leg muscle volume (mean 4,534 cm3 for men and 4,071 cm3 for women) with a mean of the absolute value of relative error with respect to MRI of 6.2 ± 3.9. The new approach suggests that BIA can reasonably estimate the distribution and volume of muscles in the lower extremities of lean subjects.
High glucose abolishes the antiproliferative effect of 17β-estradiol in human vascular smooth muscle cells
Authors: Ling Shanhong , Little Peter J. , Williams Maro R. I. , Dai Aozhi , Hashimura Kazuhiko , Liu Jun-Ping , Komesaroff Paul A. , Sudhir Krishnankutty
Published: February 2015

We examined effects of 17β-estradiol (E2) on human vascular smooth muscle cell (VSMC) proliferation under normal (5 mmol/l) and high (25 mmol/l) glucose concentrations. Platelet-derived growth factor (PDGF) BB (20 ng/ml)-induced increases in DNA synthesis and proliferation were greater in high than normal glucose concentrations; the difference in DNA synthesis was abolished by a protein kinase C (PKC)-β inhibitor, LY-379196 (30 nmol/l). Western blotting showed that PKC-β1 protein increased in cells exposed to high glucose, whereas PKC-α protein and total PKC activity remained unchanged, compared with normal glucose cultures. In normal glucose, E2 (1–100 nmol/l) inhibited PDGF-induced DNA synthesis by 18–37% and cell proliferation by 16–22% in a concentration-dependent manner. The effects of E2 were blocked by the estrogen receptor (ER) antagonist ICI-182780, indicating ER dependence. In high glucose, the inhibitory effect of E2on VSMC proliferation was abolished but was restored in the presence of the PKC-β inhibitor LY-379196. Thus high glucose enhances human VSMC proliferation and attenuates the antiproliferative effect of E2 in VSMC via activation of PKC-β.
Double isotope tracer method for measuring fractional zinc absorption: theoretical analysis
Authors: Sparacino Giovanni , Shames David M. , Vicini Paolo , King Janet C. , Cobelli Claudio
Published: February 2015

Several approaches for estimation of fractional zinc absorption (FZA) by calculating the ratio of oral to intravenous stable isotopic tracer concentrations (at an appropriate time) in urine or plasma after their simultaneous administration have been proposed in the last decade. These simple-to-implement approaches, often referred to as the double isotopic tracer ratio (DITR) method, are more attractive than the classical “deconvolution” method and the more commonly used single-tracer methods based on fecal monitoring and indicator dilution, after oral or intravenous tracer administration, respectively. However, the domain of validity of DITR for measuring FZA has recently been questioned. In this paper, we provide a theoretical justification of the validity of four different “approximate” formulations of the DITR technique by demonstrating mathematically that their accuracy is a consequence of the particular properties of zinc kinetics.
Renal substrate exchange and gluconeogenesis in normal postabsorptive humans
Authors: Meyer Christian , Stumvoll Michael , Dostou Jean , Welle Stephen , Haymond Morey , Gerich John
Published: February 2015

Release of glucose by the kidney in postabsorptive normal humans is generally regarded as being wholly due to gluconeogenesis. Although lactate is the most important systemic gluconeogenic precursor and there is appreciable net renal lactate uptake, renal lactate gluconeogenesis has not yet been investigated. The present studies were therefore undertaken to quantitate the contribution of lactate to renal gluconeogenesis and the role of the kidney in lactate metabolism. We determined systemic and renal lactate conversion to glucose as well as renal lactate net balance, fractional extraction, uptake, and release in 24 postabsorptive humans by use of a combination of isotopic and renal balance techniques. For comparative purposes, accumulated similar data for glutamine, alanine, and glycerol are also reported. Systemic lactate gluconeogenesis (1.97 ± 0.12 μmol · kg−1· min−1) was about threefold greater than that from glycerol, glutamine, and alanine. The sum of gluconeogenesis from these precursors, uncorrected for tricarboxylic acid (TCA) cycle carbon exchange, explained 34% of systemic glucose release. Renal lactate uptake (3.33 ± 0.28 μmol · kg−1· min−1) accounted for nearly 30% of its systemic turnover. Renal gluconeogenesis from lactate (0.78 ± 0.10 μmol · kg−1· min−1) was 3.5, 2.5, and 9.6-fold greater than that from glycerol, glutamine, and alanine. The sum of renal gluconeogenesis from these precursors equaled ∼40% of the sum of their systemic gluconeogenesis. When the isotopically determined rates of systemic and renal gluconeogenesis were corrected for TCA cycle carbon exchange, gluconeogenesis from these precursors accounted for 43% of systemic glucose release and 89% of renal glucose release. We conclude that 1) in postabsorptive normal humans, lactate is the dominant precursor for both renal and systemic gluconeogenesis; 2) the kidney is an important organ for lactate disposal; 3) under these conditions, renal glucose release is predominantly, if not exclusively, due to gluconeogenesis; and 4) liver and kidney are similarly important for systemic gluconeogenesis.
Do sex steroids regulate glutamine synthesis with age?
Authors: Verdier Lionel , Boirie Yves , Van Drieesche Sebastien , Mignon Michelle , Begue Rene-Jean , Meynial-Denis Dominique
Published: February 2015

Glutamine synthetase, a key enzyme in the production of glutamine, is known to be induced by glucocorticoids and preserved in skeletal muscle during aging, but the effect of other steroids, such as sex steroids (progesterone, estradiol), is unknown in vivo. The aim of this study was to determine whether progesterone or estradiol plays a role in the regulation of glutamine synthetase (GS) with aging. The effects of glucocorticoids and sex steroids on muscle GS activity and mRNA expression were measured in adult (6–8 mo; n = 7 in each group) and aged (26 mo; n= 10 in each group) female Wistar rats after adrenalectomy (ADX), ovariectomy (OV), or both (ADXOV) and were compared with those in sham-operated (Sham) control rats. In tibialis anterior muscle, ADX noticeably decreased both GS activity and expression irrespective of age (50–60%; P < 0.05), whereas OV had no effect at either age. Progesterone and estradiol replacement had no effect on the recovery of muscle GS response in either ADX or OV rats, regardless of age. In contrast, heart GS activity was decreased by ADX in aged animals only. These results suggest that the reproductive endocrine status of female rats does not affect muscle GS activity either in muscle or in heart, in young or aged animals, and that the heart GS response to steroids may be differently regulated in aged rats.
Cyr61 and CTGF are molecular markers of bladder wall remodeling after outlet obstruction
Authors: Chaqour Brahim , Whitbeck Catherine , Han Ji-Soo , Macarak Edward , Horan Pat , Chichester Paul , Levin Robert
Published: February 2015

Cysteine-rich protein (Cyr61) and connective tissue growth factor (CTGF) are key immediate early growth factors with functions in cell proliferation, differentiation, and extracellular matrix synthesis. Studies were performed to assess the gene expression profile of Cyr61 and CTGF in rat urinary bladder during growth in response to partial outlet obstruction. The mRNA levels of Cyr61 as determined by ribonuclease protection assay increased sharply after 1 day and remained elevated throughout the time period of the obstruction. This correlates well with increased bladder weight. The CTGF mRNA levels seemed to peak within the second week of the urethral obstruction and correlate well with increased type I collagen mRNA. The expression pattern of either Cyr61 or CTGF proteins corroborated that of their respective mRNAs. Immunohistochemical analyses showed that immunoreactivity of Cyr61 was confined to detrusor smooth muscle and that of CTGF was detected within both detrusor muscle and lamina propria layers. These data strongly indicate the involvement of Cyr61 and CTGF in bladder wall remodeling as a result of the outlet obstruction.
A preexercise α-lactalbumin-enriched whey protein meal preserves lipid oxidation and decreases adiposity in rats
Authors: Bouthegourd Jean-Christophe J. , Roseau Suzanne M. , Makarios-Lahham Lina , Leruyet Pascale M. , Tomé Daniel G. , Even Patrick C.
Published: February 2015

The composition of the preexercise food intake is known to affect substrate utilization during exercise and thus can affect long-term changes in body weight and composition. These parameters were measured in male rats exercised 2 h daily over 5 wk, either in the fasting state or 1 h after they ingested a meal enriched with glucose (Glc), whole milk protein (WMP), or α-lactalbumin-enriched whey protein (CPαL). Compared with fasting, the Glc meal increased glucose oxidation and decreased lipid oxidation during and after exercise. In contrast, the WMP and CPαL meals preserved lipid oxidation and increased protein oxidation, the CPαL meal increasing protein oxidation more than the WMP meal. At the end of the study, body weight was larger in the WMP-, Glc-, and CPαL-fed rats than in the fasted ones. This resulted from an increased fat mass in the WMP and Glc rats and to an increased lean body mass, particularly muscles, in the CPαL rats. We conclude that the potential of the CPαL meal to preserve lipid oxidation and to rapidly deliver amino acids for use during exercise improved the efficiency of exercise training to decrease adiposity.
Insulin increases branched-chain α-ketoacid dehydrogenase kinase expression in Clone 9 rat cells
Authors: Nellis Mary M. , Doering Christopher B. , Kasinski Andrea , Danner Dean J.
Published: February 2015

The branched-chain amino acids (BCAA) are committed to catabolism by the activity of the branched-chain α-ketoacid dehydrogenase (BCKD) complex. BCKD activity is regulated through the action of the complex-specific BCKD kinase that phosphorylates two serine residues in the E1α subunit. Greater BCKD kinase expression levels result in a lower activity state of BCKD and thus a decreased rate of BCAA catabolism. Activity state varies among tissues and can be altered by diet, exercise, hormones, and disease state. Within individual tissues, the concentration of BCKD kinase reflects the activity state of the BCKD complex. Here we investigated the effects of insulin, an important regulator of hepatic metabolic enzymes, on BCKD kinase expression in Clone 9 rat cells. Insulin effected a twofold increase in message levels and a twofold increase in BCKD kinase protein levels. The response was completely blocked by treatment with LY-294002 and partially blocked by rapamycin, thus demonstrating a dependence on phosphatidylinositol 3-kinase and mTOR function, respectively. These studies suggest that insulin acts to regulate BCAA catabolism through stimulation of BCKD kinase expression.
Similar carbohydrate but enhanced lactate utilization during exercise after 9 wk of acclimatization to 5,620 m
Authors: van Hall G. , Calbet J. A. L. , Søndergaard H. , Saltin B.
Published: February 2015

We hypothesized that reliance on lactate as a means of energy distribution is higher after a prolonged period of acclimatization (9 wk) than it is at sea level due to a higher lactate Ra and disposal from active skeletal muscle. To evaluate this hypothesis, six Danish lowlanders (25 ± 2 yr) were studied at rest and during 20 min of bicycle exercise at 146 W at sea level (SL) and after 9 wk of acclimatization to 5,260 m (Alt). Whole body glucose Ra was similar at SL and Alt at rest and during exercise. Lactate Ra was also similar for the two conditions at rest; however, during exercise, lactate Ra was substantially lower at SL (65 μmol · min−1 · kg body wt−1) than it was at Alt (150 μmol · min−1 · kg body wt−1) at the same exercise intensity. During exercise, net lactate release was ∼6-fold at Alt compared with SL, and related to this, tracer-calculated leg lactate uptake and release were both 3- or 4-fold higher at Alt compared with SL. The contribution of the two legs to glucose disposal was similar at SL and Alt; however, the contribution of the two legs to lactate Ra was significantly lower at rest and during exercise at SL (27 and 81%) than it was at Alt (45 and 123%). In conclusion, at rest and during exercise at the same absolute workload, CHO and blood glucose utilization were similar at SL and at Alt. Leg net lactate release was severalfold higher, and the contribution of leg lactate release to whole body lactate Ra was higher at Alt compared with SL. During exercise, the relative contribution of lactate oxidation to whole body CHO oxidation was substantially higher at Alt compared with SL as a result of increased uptake and subsequent oxidation of lactate by the active skeletal muscles.
Effects of free fatty acids on hepatic glycogenolysis and gluconeogenesis in conscious dogs
Authors: Chu Chang An , Sherck Stephanie M. , Igawa Kayano , Sindelar Dana K. , Neal Doss W. , Emshwiller Maya , Cherrington Alan D.
Published: February 2015

The aim of this study was to determine the effect of high levels of free fatty acids (FFA) and/or hyperglycemia on hepatic glycogenolysis and gluconeogenesis. Intralipid was infused peripherally in 18-h-fasted conscious dogs maintained on a pancreatic clamp in the presence (FFA + HG) or absence (FFA + EuG) of hyperglycemia. In the control studies, Intralipid was not infused, and euglycemia (EuG) or hyperglycemia (HG) was maintained. Insulin and glucagon were clamped at basal levels in all four groups. The arterial blood glucose level increased by 50% in the HG and FFA + HG groups. It did not change in the EuG and FFA + EuG groups. Arterial plasma FFA increased by ∼140% in the FFA + EuG and FFA + HG groups but did not change significantly either in the EuG or HG groups. Arterial glycerol levels increased by ∼150% in both groups. Overall (3-h) net hepatic glycogenolysis was 196 ± 26 mg/kg in the EuG group. It decreased by 96 ± 20, 82 ± 16, and 177 ± 22 mg/kg in the HG, FFA + EuG, and FFA + HG groups, respectively. Overall (3-h) hepatic gluconeogenic flux was 128 ± 22 mg/kg in the EuG group, but it was suppressed by 30 ± 9 mg/kg in response to hyperglycemia. It was increased by 59 ± 12 and 56 ± 10 mg/kg in the FFA + EuG and FFA + HG groups, respectively. In conclusion, an increase in plasma FFA and glycerol significantly inhibited hepatic glycogenolysis and markedly stimulated hepatic gluconeogenesis.
Postprandial leg uptake of triglyceride is greater in women than in men
Authors: Horton Tracy J. , Commerford S. Renee , Pagliassotti Michael J. , Bessesen Daniel H.
Published: February 2015

The postprandial excursion of plasma triglyceride (TG) concentration is greater in men than in women. In this study, the disposition of dietary fat was examined in lean healthy men and women ( n = 8/group) in either the overnight-fasted or fed (4.5 h after breakfast) states. A [14C]oleate tracer was incorporated into a test meal, providing 30% of total daily energy requirements. After ingestion of the test meal, measures of arteriovenous differences in TG and14C across the leg were combined with needle biopsies of skeletal muscle and adipose tissue and respiratory gas collections to define the role of skeletal muscle in the clearance of dietary fat. The postprandial plasma TG and14C tracer excursions were lower ( P = 0.04) in women than in men in the overnight-fasted and fed states. Women, however, had significantly greater limb uptake of total TG compared with men on both the fasted (3,849 ± 846 vs. 528 ± 221 total μmol over 6 h) and fed (4,847 ± 979 vs. 1,571 ± 334 total μmol over 6 h) days. This was also true for meal-derived14C lipid uptake.14C content of skeletal muscle tissue (μCi/g tissue) was significantly greater in women than in men 6 h after ingestion of the test meal. In contrast,14C content of adipose tissue was not significantly different between men and women at 6 h. The main effect of nutritional state, fed vs. fasted, was to increase the postmeal glucose ( P = 0.01) excursion (increase from baseline) and decrease the postmeal TG excursion ( P = 0.02). These results support the notion that enhanced skeletal muscle clearance of lipoprotein TG in women contributes to their reduced postprandial TG excursion. Questions remain as to the mechanisms causing these sex-based differences in skeletal muscle TG uptake and metabolism. Furthermore, nutritional state can significantly impact postprandial metabolism in both men and women.
Glucose promotes pancreatic islet β-cell survival through a PI 3-kinase/Akt-signaling pathway
Authors: Srinivasan Shanthi , Bernal-Mizrachi Ernesto , Ohsugi Mitsuru , Permutt Marshall Alan
Published: February 2015

The concentration of glucose in plasma is an important determinant of pancreatic β-cell mass, whereas the relative contributions of hypertrophy, proliferation, and cell survival to this process are unclear. Glucose results in depolarization and subsequent calcium influx into islet β-cells. Because depolarization and calcium (Ca2+) influx promote survival of neuronal cells, we hypothesized that glucose might alter survival of islet β-cells through a similar mechanism. In the present studies, cultured mouse islet β-cells showed a threefold decrease in apoptosis under conditions of 15 mM glucose compared with 2 mM glucose ( P < 0.05). MIN6 insulinoma cells incubated in 25 mM glucose for 24 h showed a threefold decrease in apoptosis compared with cells in 5 mM glucose (1.7 ± 0.2 vs. 6.3 ± 1%, respectively, P < 0.001). High glucose (25 mM) enhanced survival-required depolarization and Ca2+influx and was blocked by phosphatidylinositol (PI) 3-kinase inhibitors. Glucose activation of the protein kinase Akt was demonstrated in both insulinoma cells and cultured mouse islets by means of an antibody specific for Ser473phospho-Akt and by an in vitro Akt kinase assay. Akt phosphorylation was dependent on PI 3-kinase but not on MAPK. Transfection of insulinoma cells with an Akt kinase-dead plasmid (Akt-K179M) resulted in loss of glucose-mediated protection, whereas transfection with a constitutively active Akt enhanced survival in glucose-deprived insulinoma cells. The results of these studies defined a novel pathway for glucose-mediated activation of a PI 3-kinase/Akt survival-signaling pathway in islet β-cells. This pathway may provide important targets for therapeutic intervention.
Amniotic IGF-I supplements improve gut growth but reduce circulating IGF-I in growth-restricted fetal sheep
Authors: Bloomfield Frank H. , Bauer Michael K. , Van Zijl Pierre L. , Gluckman Peter D. , Harding Jane E.
Published: February 2015

Insulin-like growth factor I (IGF-I) is an important regulator of fetal growth, and circulating concentrations are reduced in intrauterine growth-restricted (IUGR) fetuses. We investigated whether IGF-I administered into amniotic fluid could ameliorate IUGR in fetal sheep. Fetuses were assigned to control ( n = 9), IUGR+saline ( n = 12), or IUGR+IGF-I groups (daily intra-amniotic IGF-I injections of 20 μg, n = 13). IUGR was induced by placental embolization from 114 to 120 days. Treatment was from 120 to 130 days of gestation. Embolization produced asymmetrically IUGR fetuses with decreased body weight and lighter, thinner-walled guts. Fetal plasma and amniotic IGF-I levels were reduced. During treatment, fetal plasma, but not amniotic, IGF-I levels recovered in the saline group but remained depressed in the IGF-I-treated group. IGF-I treatment restored gut weight and wall thickness to control levels and increased the number of crypt mitoses. Fetal weight was similar to that of controls, but spleen, liver, and thymic weights were reduced by 30–37%, and placentome growth was altered. Amniotic fluid IGF-I supplementation may provide the basis of future therapeutic approaches to IUGR, but the systemic effects require further investigation.
Effect of hepatic denervation on peripheral insulin sensitivity in conscious dogs
Authors: Moore Mary Courtney , Satake Shosuke , Baranowski Bryan , Hsieh Po-Shiuan , Neal Doss W. , Cherrington Alan D.
Published: February 2015

We tested the hypothesis that the loss of hepatic nerves decreases peripheral insulin sensitivity. Surgical hepatic denervation (DN) was performed in 22 dogs ∼16 days before study; 7 dogs (Sham-Sal) had a sham procedure. A euglycemic hyperinsulinemic (1 mU · kg−1· min−1; arterial insulin 35 ± 1 μU/ml in all dogs) clamp was performed in conscious dogs. From 0 to 90 min of the clamp, all dogs received the same treatment; then the DN dogs were divided into three groups. From 90 to 180 min, DN-PeA ( n = 7) and DN-PoA ( n = 7) groups received acetylcholine 2.5 μg · kg−1· min−1via peripheral or portal vein, respectively, and DN-Sal ( n= 8) received no acetylcholine. During 150–180 min, the Sham-Sal, DN-Sal, DN-PeA, and DN-PoA groups exhibited glucose infusion rates of 12.4 ± 0.8, 9.3 ± 0.8 ( P < 0.05 vs. Sham-Sal), 9.1 ± 0.1 ( P < 0.05 vs. Sham-Sal), and 12.7 ± 1.6 mg · kg−1· min−1; nonhepatic glucose uptakes of 11.5 ± 0.9, 8.9 ± 0.7 ( P < 0.05 vs. Sham-Sal), 8.6 ± 0.9 ( P < 0.05 vs. Sham-Sal), and 11.9 ± 1.7 mg · kg−1· min−1; net hindlimb glucose uptakes of 18.4 ± 2.1, 13.7 ± 1.1 ( P< 0.05 vs. Sham-Sal), 17.5 ± 1.9, and 16.7 ± 3.2 mg/min; and glucose utilization rates of 14.4 ± 1.4, 10.4 ± 0.8 ( P < 0.05 vs. Sham-Sal), 9.8 ± 0.9 ( P< 0.05 vs. Sham-Sal), and 13.6 ± 1.8 mg · kg−1· min−1, respectively. DN caused peripheral insulin resistance, and intraportal but not peripheral acetylcholine restored insulin sensitivity.
Effects of thyroid state on the expression of hepatic thyroid hormone transporters in rats
Authors: Peeters Robin P. , Friesema Edith C. H. , Docter Roel , Hennemann Georg , Visser Theo J.
Published: February 2015

Liver uptake of thyroxine (T4) is mediated by transporters and is rate limiting for hepatic 3,3′,5-triiodothyronine (T3) production. We investigated whether hepatic mRNA for T4transporters is regulated by thyroid state using Xenopus laevis oocytes as an expression system. Because X. laevis oocytes show high endogenous uptake of T4, T4 sulfamate (T4NS) was used as an alternative ligand for the hepatic T4 transporters. Oocytes were injected with 23 ng liver mRNA from euthyroid, hypothyroid, or hyperthyroid rats, and after 3–4 days uptake was determined by incubation of injected and uninjected oocytes for 1 h at 25°C or for 4 h at 18°C with 10 nM [125I]T4NS. Expression of type I deiodinase (D1), which is regulated by thyroid state, was studied in the oocytes as an internal control. Uptake of T4NS showed similar approximately fourfold increases after injection of liver mRNA from euthyroid, hypothyroid, or hyperthyroid rats. A similar lack of effect of thyroid state was observed using reverse T3 as ligand. In contrast, D1 activity induced by liver mRNA from hyperthyroid and hypothyroid rats in the oocytes was 2.4-fold higher and 2.7-fold lower, respectively, compared with euthyroid rats. Studies have shown that uptake of iodothyronines in rat liver is mediated in part by several organic anion transporters, such as the Na+/taurocholate-cotransporting polypeptide (rNTCP) and the Na-independent organic anion-transporting polypeptide (rOATP1). Therefore, the effects of thyroid state on rNTCP, rOATP1, and D1 mRNA levels in rat liver were also determined. Northern analysis showed no differences in rNTCP or rOATP1 mRNA levels between hyperthyroid and hypothyroid rats, whereas D1 mRNA levels varied widely as expected. These results suggest little effect of thyroid state on the levels of mRNA coding for T4 transporters in rat liver, including rNTCP and rOATP1. However, they do not exclude regulation of hepatic T4 transporters by thyroid hormone at the translational and posttranslational level.
Specificity of thyroid hormone receptor subtype and steroid receptor coactivator-1 on thyroid hormone action
Authors: Sadow Peter M. , Chassande Olivier , Gauthier Karine , Samarut Jacques , Xu Jianming , O′Malley Bert W. , Weiss Roy E.
Published: February 2015

Isoforms of the thyroid hormone receptor ( TR) α and TRβ genes mediate thyroid hormone action. How TR isoforms modulate tissue-specific thyroid hormone (TH) action remains largely unknown. The steroid receptor coactivator-1 (SRC-1) is among a group of transcriptional coactivator proteins that bind to TRs, along with other members of the nuclear receptor superfamily, and modulate the activity of genes regulated by TH. Mice deficient in SRC-1 possess decreased tissue responsiveness to TH and many steroid hormones; however, it is not known whether or not SRC-1-mediated activation of TH-regulated gene transcription in peripheral tissues, such as heart and liver, is TR isoform specific. We have generated mice deficient in TRα and SRC-1, as well as in TRβ and SRC-1, and investigated thyroid function tests and effects of TH deprivation and TH treatment compared with wild-type (WT) mice or those deficient in either TR or SRC-1 alone. The data show that 1) in the absence of TRα or TRβ, SRC-1 is important for normal growth; 2) SRC-1 modulates TRα and TRβ effects on heart rate; 3) two new TRβ-dependent markers of TH action in the liver have been identified, osteopontin (upregulated) and glutathione S-transferase (downregulated); and 4) SRC-1 may mediate the hypersensitivity to TH seen in liver of TRα-deficient mice.
Regulation of urea synthesis by agmatine in the perfused liver: studies with15N
Authors: Nissim Itzhak , Horyn Oksana , Daikhin Yevgeny , Nissim Ilana , Lazarow Adam , Yudkoff Marc
Published: February 2015

Administration of arginine or a high-protein diet increases the hepatic content of N-acetylglutamate (NAG) and the synthesis of urea. However, the underlying mechanism is unknown. We have explored the hypothesis that agmatine, a metabolite of arginine, may stimulate NAG synthesis and, thereby, urea synthesis. We tested this hypothesis in a liver perfusion system to determine 1) the metabolism ofl-[ guanidino-15N2]arginine to either agmatine, nitric oxide (NO), and/or urea; 2) hepatic uptake of perfusate agmatine and its action on hepatic N metabolism; and 3) the role of arginine, agmatine, or NO in regulating NAG synthesis and ureagenesis in livers perfused with15N-labeled glutamine and unlabeled ammonia or15NH4Cl and unlabeled glutamine. Our principal findings are 1) [ guanidino-15N2]agmatine is formed in the liver from perfusatel-[ guanidino-15N2]arginine (∼90% of hepatic agmatine is derived from perfusate arginine); 2) perfusions with agmatine significantly stimulated the synthesis of15N-labeled NAG and [15N]urea from15N-labeled ammonia or glutamine; and 3) the increased levels of hepatic agmatine are strongly correlated with increased levels and synthesis of15N-labeled NAG and [15N]urea. These data suggest a possible therapeutic strategy encompassing the use of agmatine for the treatment of disturbed ureagenesis, whether secondary to inborn errors of metabolism or to liver disease.
Metabolic costs of isometric force generation and maintenance of human skeletal muscle
Authors: Russ David W. , Elliott Mark A. , Vandenborne Krista , Walter Glenn A. , Binder-Macleod Stuart A.
Published: February 2015

During isometric contractions, no true work is performed, so the force-time integral (FTI) is often used to approximate isometric work. However, the relationship between FTI and metabolic cost is not as linear. We tested the hypothesis that this nonlinearity was due to the cost of attaining a given force being greater than that of maintaining it. The ATP consumed per contraction in the human medial gastrocnemius muscle ( n = 6) was determined by use of 31P-NMR spectroscopy during eight different electrical stimulation protocols. Each protocol consisted of 8 trains of a single frequency (20 or 80 Hz) and duration (300, 600, 1,200, or 1,800 ms) performed under ischemic conditions. The cost of force generation was determined from the ATP turnover during the short-duration trains that did not attain a steady force level. Estimates of the cost of force maintenance at each frequency were determined by subtracting the ATP turnover during the shorter-duration trains from the turnover during the long-duration trains. The force generation phase of an isometric contraction was indeed more metabolically costly than the force maintenance phase during both 20- and 80-Hz stimulation. Thus the mean rate of ATP hydrolysis appeared to decline as contraction duration increased. Interestingly, the metabolic costs of maintaining force during 20-Hz and 80-Hz stimulation were comparable, although different levels of force were produced.
High sensitivity of rat hepatic vitamin D3-25 hydroxylaseCYP27Ato 1,25-dihydroxyvitamin D3administration
Authors: Theodoropoulos Catherine , Demers Christian , Petit Jean-Luc , Gascon-Barré Marielle
Published: February 2015

CYP27A is considered the main vitamin D3(D3)-25 hydroxylase in humans. Our purpose was to evaluate the effect of the D3nutritional and hormonal status on hepatic CYP27A mRNA, cellular distribution, transcription rate, and enzyme activity. Studies were carried out in normal and in D-depleted rats supplemented with D3, 25OHD3, or 1,25(OH)2D3. CYP27A exhibited a significant gender difference and was observed throughout the hepatic acinus not only in hepatocytes but also in sinusoidal endothelial, stellate, and Kupffer cells. Neither D3nor 25OHD3influenced CYP27A mRNA levels. However, 1,25(OH)2D3repletion led to a 60% decrease in CYP27A mRNA, which was accompanied by a 46% decrease in mitochondrial D3-25 hydroxylase activity. The effect of 1,25(OH)2D3was mediated by a significant decrease in CYP27A transcription, whereas its mRNA half-life remained unchanged. Our data indicate that CYP27A is present in hepatic parenchymal and sinusoidal cells and that the gene transcript is not influenced by the D3nutritional status but is transcriptionally regulated by 1,25(OH)2D3exposure.
Resistance of adipose tissue lipoprotein lipase to insulin action in rats fed an obesity-promoting diet
Authors: Picard Frédéric , Boivin André , Lalonde Josée , Deshaies Yves
Published: February 2015

This study aimed to assess whether adipose lipoprotein lipase (LPL) becomes resistant to insulin in a nutritional model of resistance of glucose metabolism to insulin. Sprague-Dawley rats were fed for 4 wk chow or a purified high-sucrose, high-fat (HSHF) diet that induced overt insulin resistance. Rats were fasted for 24 h and then refed chow for 1, 3, or 6 h. The postprandial rise in insulinemia was similar in both dietary cohorts, whereas glycemia was higher in HSHF-fed than in chow-fed animals, indicating glucose intolerance and insulin resistance. In chow-fed rats, adipose LPL activity increased two- to fourfold postprandially, but only minimally (30%) in HSHF-fed rats. Muscle LPL decreased postprandially in HSHF-fed rats, suggesting intact sensitivity to insulin, but it increased in chow-fed animals. Peak postprandial triglyceridemia was higher (+70%) in insulin-resistant than in control rats. The postprandial rate of appearance of triglycerides in the circulation was similar in control and insulin-resistant rats, indicating that hypertriglyceridemia of the latter was the result of impaired clearance. These results demonstrate that adipose LPL becomes resistant to insulin in diet-induced IR and further suggest that, under certain nutritional conditions, modifications in adipose LPL modulation associated with insulin resistance, along with low muscle LPL, heightens postprandial hypertriglyceridemia through attenuated triglyceride clearance.
Disruption of pubertal onset by exogenous testosterone and estrogen in two species of rodents
Authors: Pak Toni R. , Lynch G. Robert , Ziegler D. Matthew , Lunden Jason B. , Tsai Pei-San
Published: February 2015

The administration of adult physiological levels of testosterone (T) and 17β-estradiol (E2) to male Siberian hamsters was previously shown to delay the onset of puberty. To examine whether this is a response common to other rodents, we investigated whether exogenous steroids also alter the onset of puberty in Syrian hamsters and mice. Juvenile male Syrian hamsters and mice were implanted with Silastic capsules containing T, E2, or cholesterol control. After 15 days, plasma, pituitaries, and testes were processed for histological analysis or measurements of gonadotropins and circulating steroid hormones. T and E2implants reduced testis mass and gonadotropin stores in both species and arrested spermatogenesis in Syrian hamsters. In contrast, spermatogenesis in mice was unaffected by T and only modestly affected by E2. Although E2 inhibited circulating follicle-stimulating hormone (FSH) in both species, T inhibited circulating FSH in mice only. Overall, our results demonstrate that the hypothalamic-pituitary-gonadal axis of each rodent species responds uniquely to T and E2 during the pubertal transition. Despite the highly varied effects of T and E2 in these two species, the ability of steroid hormones to disrupt the onset of puberty appears to be a feature common to many rodents.
Muscle contraction increases lactate transport while reducing sarcolemmal MCT4, but not MCT1
Authors: Tonouchi Mio , Hatta Hideo , Bonen Arend
Published: February 2015

Rates of lactate uptake into giant sarcolemmal vesicles were determined in vesicles collected from rat muscles at rest and immediately after 10 min of intense muscle contraction. This contraction period reduced muscle glycogen rapidly by 37–82% in all muscles examined ( P < 0.05) except the soleus muscle (no change P > 0.05). At an external lactate concentration of 1 mM lactate, uptake into giant sarcolemmal vesicles was not altered ( P > 0.05), whereas at an external lactate concentration of 20 mM, the rate of lactate uptake was increased by 64% ( P < 0.05). Concomitantly, the plasma membrane content of monocarboxylate transporter (MCT)1 was reduced slightly (−10%, P < 0.05), and the plasma membrane content of MCT4 was reduced further (−25%, P < 0.05). In additional studies, the 10-min contraction period increased the plasma membrane GLUT4 ( P < 0.05) while again reducing MCT4 (−20%, P < 0.05) but not MCT1 ( P > 0.05). These studies have shown that intense muscle contraction can increase the initial rates of lactate uptake, but only when the external lactate concentrations are high (20 mM). We speculate that muscle contraction increases the intrinsic activity of the plasma membrane MCTs, because the increase in lactate uptake occurred while plasma membrane MCT4 was decreased and plasma membrane MCT1 was reduced only minimally, or not at all.
Aging and insulin secretion
Authors: Chang Annette M. , Halter Jeffrey B.
Published: February 2015

Glucose tolerance progressively declines with age, and there is a high prevalence of type 2 diabetes and postchallenge hyperglycemia in the older population. Age-related glucose intolerance in humans is often accompanied by insulin resistance, but circulating insulin levels are similar to those of younger people. Under some conditions of hyperglycemic challenge, insulin levels are lower in older people, suggesting β-cell dysfunction. When insulin sensitivity is controlled for, insulin secretory defects have been consistently demonstrated in aging humans. In addition, β-cell sensitivity to incretin hormones may be decreased with advancing age. Impaired β-cell compensation to age-related insulin resistance may predispose older people to develop postchallenge hyperglycemia and type 2 diabetes. An improved understanding of the metabolic alterations associated with aging is essential for the development of preventive and therapeutic interventions in this population at high risk for glucose intolerance.
Calcitropic gene expression suggests a role for the intraplacental yolk sac in maternal-fetal calcium exchange
Authors: Kovacs Christopher S. , Chafe Linda L. , Woodland Mandy L. , McDonald Kirsten R. , Fudge Neva J. , Wookey Peter J.
Published: February 2015

The expression of calcitropic genes and proteins was localized within murine placenta during late gestation (the time frame of active calcium transfer) with an analysis of several gene-deletion mouse models by immunohistochemistry and in situ hybridization. Parathyroid hormone-related protein (PTHrP), the PTH/PTHrP receptor, calcium receptor, calbindin-D9k, Ca2+-ATPase, and vitamin D receptor were all highly expressed in a localized structure of the murine placenta, the intraplacental yolk sac, compared with trophoblasts. In the PTHrP gene-deleted or Pthrp-null placenta in which placental calcium transfer is decreased, calbindin-D9kexpression was downregulated in the intraplacental yolk sac but not in the trophoblasts. These observations indicated that the intraplacental yolk sac contains calcium transfer and calcium-sensing capability and that it is a probable route of maternal-fetal calcium exchange in the mouse.
Effects of caloric restriction on mitochondrial function and gene transcripts in rat muscle
Authors: Sreekumar R. , Unnikrishnan J. , Fu A. , Nygren J. , Short K. R. , Schimke J. , Barazzoni R. , Nair K. Sreekumaran
Published: February 2015

Rodent skeletal muscle mitochondrial DNA has been shown to be a potential site of oxidative damage during aging. Caloric restriction (CR) is reported to reduce oxidative stress and prolong life expectancy in rodents. Gene expression profiling and measurement of mitochondrial ATP production capacity were performed in skeletal muscle of male rats after feeding them either a control diet or calorie-restricted diet (60% of control diet) for 36 wk to determine the potential mechanism of the beneficial effects of CR. CR enhanced the transcripts of genes involved in reactive oxygen free radical scavenging function, tissue development, and energy metabolism while decreasing expression of those genes involved in signal transduction, stress response, and structural and contractile proteins. Real-time PCR measurments confirmed the changes in transcript levels of cytochrome- c oxidase III, superoxide dismutase (SOD)1, and SOD2 that were noted by the microarray approach. Mitochondrial ATP production and citrate synthase were unaltered by the dietary changes. We conclude that CR alters transcript levels of several genes in skeletal muscle and that mitochondrial function in skeletal muscle remains unaltered by the dietary intervention. Alterations in transcripts of many genes involved in reactive oxygen scavenging function may contribute to the increase in longevity reported with CR.
Glutamine and leucine nitrogen kinetics and their relation to urea nitrogen in newborn infants
Authors: Parimi Prabhu S. , Devapatla Srisatish , Gruca Lourdes , O'Brien Alicia M. , Hanson Richard W. , Kalhan Satish C.
Published: February 2015

Glutamine kinetics and its relation to transamination of leucine and urea synthesis were quantified in 16 appropriate-for-gestational-age infants, four small-for-gestational-age infants, and seven infants of diabetic mothers. Kinetics were measured between 4 and 5 h after the last feed (fasting) and in response to formula feeding using [5-15N]glutamine, [1-13C,15N]leucine, [2H5]phenylalanine, and [15N2]urea tracers. Leucine nitrogen and glutamine kinetics during fasting were significantly higher than those reported in adults. De novo synthesis accounted for ∼85% of glutamine turnover. In response to formula feeding, a significant increase ( P = 0.04) in leucine nitrogen turnover was observed, whereas a significant decrease ( P = 0.002) in glutamine and urea rate of appearance was seen. The rate of appearance of leucine nitrogen was positively correlated ( r2= 0.59, P = 0.001) with glutamine turnover. Glutamine flux was negatively correlated ( r2= 0.39, P = 0.02) with the rate of urea synthesis. These data suggest that, in the human newborn, glutamine turnover is related to a high anaplerotic flux into the tricarboxylic acid cycle as a consequence of a high rate of protein turnover. The negative relationship between glutamine turnover and the irreversible oxidation of protein (urea synthesis) suggests an important role of glutamine as a nitrogen source for other synthetic processes and accretion of body proteins.