bluuebunny/crossref_metadata_2025 huggingface dataset:
A minimal model for human whole body cholesterol metabolism
Authors: Ostlund R. E.
Published: December 2017

Important work by others has shown that human whole body cholesterol metabolism can be described by a three-compartment model computed from plasma cholesterol specific activity after an intravenous infusion of labeled cholesterol. However, some parameters of that model cannot be estimated precisely [coefficient of variation (CV) 15-19% after 40 wk of follow-up], making its use in routine clinical investigation difficult. On the other hand, a simpler two-compartment model can be calculated with excellent precision from only 10 wk of data (CV 2-8%), but its parameters are inaccurate (for example, the size of the central pool is overestimated by 20%, and the rate constant for fractional excretion of cholesterol from the body is underestimated by 15%). Thus both three-compartment and two-compartment models of cholesterol turnover have important limitations. An alternative is provided by a minimal model that takes advantage of the increased precision expected in the solution of models with fewer parameters. A three-compartment structure is used, but only four (rather than 6 or more) parameters are calculated: the mass of the rapidly mixing central cholesterol compartment, the fractional rate of cholesterol elimination from the body, and the average forward and reverse rate constants for cholesterol transfer between the rapid compartment and both slower compartments. Each of these parameters can be determined unambiguously (without the need to use a minimum or maximum estimate), accurately (mean values within 2% of theory), and with precision (CV 3-13%).(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence that intrarenal bradykinin plays a role in regulation of renal function
Authors: Siragy H. M.
Published: December 2017

Bradykinin (BK) is produced by the kidney, but the role of the renal kallikrein-kinin system (KKS) in the control of renal function is not understood. We studied the effects of intrarenal infusion of the BK antagonist, D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Phe-Thi-Arg-trifluoroacetic acid (BKA, n = 5) and BK (n = 4) alone or combined with antagonist (BKA 0.025 ng.kg-1 x min-1 + BK 0.25 ng.kg-1 x min-1, n = 4) in uninephrectomized conscious dogs in sodium balance at 10 and 80 meq/day. During low sodium intake, administration of BKA (infusions from 0.025 to 2.5 ng.kg-1 x min-1) caused a significant antidiuresis (P < 0.0001) and antinatriuresis (P < 0.0001) and a decrease in fractional sodium excretion (P < 0.0001). There were no changes in estimated renal plasma flow (RPF) or glomerular filtration rate during intrarenal administration of BKA at 0.025 and 0.25 ng.kg-1 x min-1. A dose of 2.5 ng.kg-1 x min-1 BKA caused a significant decrease in RPF. There were no changes in plasma aldosterone concentration, plasma renin activity, or systemic arterial pressure during intrarenal BKA administration. At 80 meq/day sodium balance (n = 5), intrarenal administration of BKA did not cause any systemic or renal effects. Intrarenal administration of BK at 0.25 ng.kg-1 x min-1 during low sodium balance caused an increase in urine flow rate and urinary sodium excretion. Coinfusion of BK with BKA completely abrogated the renal excretory changes induced by BKA. These data suggest that intrarenal KKS plays a role in control of renal function largely by a tubular mechanism during low sodium intake.
Mechanism of oxidative stress in skeletal muscle atrophied by immobilization
Authors: Kondo H. , Nakagaki I. , Sasaki S. , Hori S. , Itokawa Y.
Published: December 2017

To clarify the mechanism of oxidative stress in skeletal muscle atrophied by immobilization, we measured the activities of antioxidant enzymes and xanthine oxidase (XOD) and carried out the cytochemical study of hydrogen peroxide in a typical slow red muscle, the soleus. Male Wistar rats (15 wk old), of which ankle joints of one hindlimb were immobilized in the fully extended position, were killed after 4, 8, or 12 days. The activities of Mn-containing superoxide dismutase (Mn-SOD), Cu-Zn-containing superoxide dismutase (Cu-Zn-SOD), Se-dependent glutathione peroxidase (Se-GSHPx), glutathione S-transferase, catalase, and glutathione reductase were measured spectrophotometrically. The XOD activity and the concentrations of hypoxanthine, xanthine, and urate were measured using a high-performance liquid chromatography. The cytochemical study of hydrogen peroxide in short-term organ culture was performed using an electron microscope. Increased Cu-Zn-SOD and decreased Mn-SOD in atrophy might reflect increased generation of superoxide anions in the cytoplasm rather than in the mitochondria. The source of superoxide anions in the cytoplasm might be the increased superoxide-producing XOD. Enhanced generation of superoxide anions and increased Cu-Zn-SOD activity in atrophy suggested the enhanced generation of hydrogen peroxide in the cytoplasm. Due to the unchanged activity of Se-GSHPx and the unchanged or slightly increased activity of catalase in atrophy, the ability to degrade hydrogen peroxide might not increase so much. Hence, hydrogen peroxide is expected to be increased in atrophy. The cytochemical study supported this expectation.(ABSTRACT TRUNCATED AT 250 WORDS)
Ten days of exercise training reduces glucose production and utilization during moderate-intensity exercise
Authors: Mendenhall L. A. , Swanson S. C. , Habash D. L. , Coggan A. R.
Published: December 2017

We have previously shown that 12 wk of endurance training reduces the rate of glucose appearance (Ra) during submaximal exercise (Coggan, A. R., W. M. Kohrt, R. J. Spina, D. M. Bier, and J. O. Holloszy. J. Appl. Physiol. 68: 990-996, 1990). The purpose of the present study was to examine the time course of and relationship between training-induced alterations in glucose kinetics and endocrine responses during prolonged exercise. Accordingly, seven men were studied during 2 h of cycle ergometer exercise at approximately 60% of pretraining peak oxygen uptake on three occasions: before, after 10 days, and after 12 wk of endurance training. Ra was determined using a primed, continuous infusion of [6,6-2H]glucose. Ten days of training reduced mean Ra during exercise from 36.9 +/- 3.3 (SE) to 28.5 +/- 3.4 mumol.min-1.kg-1 (P < 0.001). Exercise-induced changes in insulin, C-peptide, glucagon, norepinephrine, and epinephrine were also significantly blunted. After 12 wk of training, Ra during exercise was further reduced to 21.5 +/- 3.1 mumol.min-1.kg-1 (P < 0.001 vs. 10 days), but hormone concentrations were not significantly different from 10-day values. The lower glucose Ra during exercise after short-term (10 days) training is accompanied by, and may be due to, altered plasma concentrations of the major glucoregulatory hormones. However, other adaptations must be responsible for the further reduction in Ra with more prolonged training.
Prostaglandin F2 alpha releases calcium from a thapsigargin-sensitive pool in ovine large luteal cells
Authors: Wegner J. A. , Martinez-Zaguilan R. , Gillies R. J. , Hoyer P. B.
Published: December 2017

Thapsigargin (TG) and A23187 were used to examine the regulation of cytosolic free calcium (Cai2+) in ovine large and small luteal cells. Thapsigargin (50 nM) induced a sustained increase of Cai2+ in fura 2-acetoxymethyl ester (AM)-loaded cells (large = 1.32 +/- 0.07-fold, small = 1.45 +/- 0.07-fold, P < 0.05). A23187 (1 microM) induced a rapid transient increase of Cai2+ (large = 1.37 +/- 0.07-fold, small = 1.46 +/- 0.10-fold, P < 0.05). In large cells, 0.5 microM prostaglandin F2 alpha (PGF2 alpha) increased Cai2+ 1.54 +/- 0.11-fold. Pretreatment with 50 nM TG abolished the PGF2 alpha-induced calcium response. Pretreatment with PGF2 alpha attenuated (P < 0.05) the TG-induced Cai2+ increase. Progesterone secretion was significantly (P < 0.05) inhibited by incubation with 50 nM TG, 1 microM A23187, and 0.5 microM PGF2 alpha in large but not small cells. These data suggest that PGF2 alpha releases calcium from a TG-sensitive intracellular calcium pool in ovine large luteal cells.
Pre- and posttranslational upregulation of muscle-specific glycogen synthase in athletes
Authors: Vestergaard H. , Andersen P. H. , Lund S. , Schmitz O. , Junker S. , Pedersen O.
Published: December 2017

Expression of muscle-specific glycogen synthase (GS) and phosphofructokinase (PFK) was analyzed in seven athletes and eight control subjects who were characterized using the euglycemic, hyperinsulinemic (2 mU.kg-1.min-1) clamp technique in combination with indirect calorimetry and biopsy sampling of vastus lateralis muscle. In the basal state, total GS activity and half-maximal GS activation by glucose 6-phosphate (G-6-P) were respectively 34% (P < 0.03) and 50% (P < 0.005) higher in athletes than in control subjects. In parallel, GS mRNA/microgram total RNA in athletes was 40% (P < 0.005) higher. No difference in GS immunoreactive protein abundance was found between the groups. PFK activity and protein levels were respectively 15% (P < 0.05) and 20% (P < 0.02) lower in athletes, whereas no differences was found in the level of PFK mRNA. After 4 h of hyperinsulinemia, total glucose disposal rate (P < 0.005) and both nonoxidative (P < 0.02) and oxidative (P < 0.03) glucose metabolism were significantly higher in athletes. In parallel, after hyperinsulinemia, the relative activation of GS by G-6-P was significantly higher in athletes, whereas total activity and gene expression of both GS and PFK were unaffected by insulin. We conclude that athletes have increased whole body insulin-stimulated nonoxidative glucose metabolism associated with both pretranslational (mRNA) and posttranslational (enzyme activity) upregulation of GS. However, the immunoreactive mass of GS is normal, emphasizing that posttranslational regulation of the GS protein activity is important for the increased glycogen synthesis rate of muscle in endurance-trained individuals.
Increase in insulin-like growth factor I in hypertrophying smooth muscle
Authors: Chen Y. , Bornfeldt K. E. , Arner A. , Jennische E. , Malmqvist U. , Uvelius B. , Arnqvist H. J.
Published: December 2017

The present study focuses on the role of the insulin-like growth factor (IGF) system in the development of smooth muscle hypertrophy. Hypertrophy was initiated by partial ligation of portal vein or urethra in female Sprague-Dawley rats weighing approximately 220 g. Levels of mRNA were analyzed by solution hybridization. Seven days after ligation, the wet weight of the portal vein was increased about threefold and the concentration of IGF-I mRNA was increased fourfold. The bladder wet weight was increased twofold 3 days after ligation and fourfold 10 days after ligation. IGF-I mRNA in the bladder was elevated 3-fold after 3 days and 2.5-fold after 10 days, whereas IGF binding protein 2 mRNA was increased approximately 2-fold after 3 days and 5-fold after 10 days. IGF-I receptor mRNA in the hypertrophying bladder remained unchanged. Increased levels of IGF-I were demonstrated with immunohistochemistry in both hypertrophying portal vein and urinary bladder. The results show a specific increase in IGF-I mRNA as well as an increased IGF-I immunoreactivity during hypertrophy of smooth muscle, which suggests that the local IGF-system may play a role in smooth muscle hypertrophy.
Isotopomer spectral analysis of cholesterol synthesis: applications in human hepatoma cells
Authors: Kelleher J. K. , Kharroubi A. T. , Aldaghlas T. A. , Shambat I. B. , Kennedy K. A. , Holleran A. L. , Masterson T. M.
Published: December 2017

Cholesterol synthesis from 13C-labeled precursors produces a discrete spectrum of mass isotopomers detectable using gas chromatography-mass spectrometry. The isotopomer spectral analysis (ISA) method matches the observed spectrum of cholesterol isotopomers with a mathematical model to obtain the best fit of model spectrum to data spectrum. The model was based on multinomial probability expressions that simulate cholesterol synthesis as a condensation of mevalonate fragments. As many as four unknown parameters, representing fluxes between compartments, were included in the model. Models were developed to assess cholesterol synthesis from 13C-enriched precursors including mevalonate, acetate, acetoacetate or octanoate. Models were tested in the human hepatoma cell line, Hep G2, which readily incorporated the 13C substrates into cholesterol. The ISA approach was used to estimate the fractional amount of the cholesterol precursors derived from the 13C substrate and the fraction of total cellular cholesterol synthesized in the presence of the 13C substrate. The study demonstrated the feasibility of the ISA approach for a condensation biosynthesis that is not a simple polymerization and for models with more than two unknown parameters.
Effects of i.v. amino acids on human splanchnic and whole body oxygen consumption, blood flow, and blood temperatures
Authors: Brundin T. , Wahren J.
Published: December 2017

The thermic effect of amino acid administration was examined in healthy subjects. Pulmonary and splanchnic oxygen uptake, cardiac output, splanchnic blood flow, and blood temperatures were measured in eight healthy men before and during 2.5 h of intravenous infusion of 600 kJ of a mixture of 19 amino acids. Indirect calorimetry and catheter techniques were used, including thermometry in arterial and a hepatic venous blood. During the infusion, pulmonary oxygen uptake rose progressively from a basal value of 269 +/- 6 to 321 +/- 8 ml/min after 2.5 h. The splanchnic oxygen consumption increased from a basal level of 64 +/- 4 to a peak value of 91 +/- 7 ml/min after 2 h of infusion. The 2.5 h average splanchnic proportion of the amino acid-induced whole body thermogenesis was 51 +/- 11%. Cardiac output increased from 6.2 +/- 0.3 in the basal state to 7.3 +/- 0.4 l/min, whereas the splanchnic blood flow remained unchanged during the infusion period. The arteriohepatic venous oxygen difference increased from 51 +/- 4 in the basal state to 65 +/- 5 ml/l after 2 h of amino acid infusion. The blood temperature rose by approximately 0.25 degrees C during the amino acid infusion, reflecting an increased heat accumulation in the body. It is concluded that the splanchnic tissues account for approximately one-half of the amino acid-induced whole body thermogenesis, that amino acid infusion augments blood flow in the extrasplanchnic but not in the splanchnic tissues, and stimulates the accumulation of heat in the body most likely via a resetting of the central thermosensors.
Interactions between TGF-beta and adrenocorticotropin in growth regulation of human adrenal fetal zone cells
Authors: Stankovic A. K. , Grizzle W. E. , Stockard C. R. , Parker C. R.
Published: December 2017

The factors that regulate growth and function of the human adrenal gland during intrauterine development and thereafter are ill defined. Whereas others have reported that adrenocorticotropic hormone (ACTH) augments the inhibitory effect of transforming growth factor-beta (TGF-beta) on growth of fetal zone (FZ) cells of the human fetal adrenal, we recently found that ACTH interferes with TGF-beta's inhibition of growth of fetal adrenal neocortex cells. In this study we sought to assess independently the effects of TGF-beta in the absence and presence of ACTH on growth of FZ cells. TGF-beta, in a time- and dose-dependent manner, inhibited growth (i.e., [3H]thymidine incorporation) of FZ cells. ACTH (Cortrosyn), at 90 pM to 90 nM, was found to interfere with the TGF-beta inhibition of FZ growth. ACTH 1-24 and human ACTH 1-39, both from Sigma Chemical, also were found to blunt the response of FZ cells to TGF-beta. Growth inhibition due to TGF-beta action and the reversal by ACTH of TGF-beta effects on FZ cell growth were confirmed by the results of immunohistochemical analyses of 5'-bromo-2'-deoxyuridine incorporation into nuclei of FZ cells and by indirect evaluations of cell numbers. Both forskolin (10 microM) and dibutyryl adenosine 3',5'-cyclic monophosphate (1 mM), but not phorbol 12-myristate 13-acetate (1 or 100 mM), were able to mimic ACTH actions in blunting the inhibitory effects of TGF-beta on DNA synthesis. We conclude that ACTH, possibly via activation of adenylate cyclase, interferes with, rather than augments, the growth-inhibitory effect of TGF-beta on FZ cell growth.
Development and regulation of glucose transporter and hexokinase expression in rat
Authors: Postic C. , Leturque A. , Printz R. L. , Maulard P. , Loizeau M. , Granner D. K. , Girard J.
Published: December 2017

The ontogenesis of the glucose transporters GLUT-1, GLUT-2, and GLUT-4 and the hexokinases HK-I, HK-II, and HK-IV (glucokinase) was studied in rat tissues. In brown adipose tissue, high levels of GLUT-4 and HK-II were observed during fetal life; both decreased at birth and then increased throughout development. At birth, cold exposure increased GLUT-4 and HK-II expression in brown adipose tissue, whereas fasting decreased it. GLUT-1 and HK-I were present in fetal muscle, but GLUT-4 and HK-II were absent. The coordinate appearance of GLUT-4 and HK-II in skeletal muscle was concomitant with the acquisition of insulin sensitivity after weaning. In the heart, the glucose transporter isoform switched from GLUT-1 to GLUT-4 during the suckling period. The coordinate expression of GLUT-4 and HK-II in heart was observed after weaning. GLUT-2, detected in fetal liver, increased throughout development. GLUT-1 and HK-I were detectable in fetal liver, whereas glucokinase appeared after weaning. Consumption of a high-carbohydrate diet after weaning increased GLUT-4 and HK-II in muscle and GLUT-2 in liver, whereas consumption of a high-fat diet prevented these changes. These results showed that 1) GLUT-1 and HK-I are abundant in most fetal rat tissues, 2) GLUT-4 and HK-II expression is associated with the appearance of tissue insulin sensitivity, and 3) GLUT-2 is expressed early in liver, before the appearance of glucokinase.
Arterial alpha-adrenergic responsiveness is decreased and SNS activity is increased in older humans
Authors: Hogikyan R. V. , Supiano M. A.
Published: December 2017

We tested the hypotheses that 1) there is an age-associated decrease in arterial alpha-adrenergic responsiveness and 2) there is upregulation of this response during suppression of sympathetic nervous system (SNS) activity. We measured forearm blood flow (FABF) by plethysmography during brachial artery infusions of the alpha-adrenergic agonist norepinephrine (NE) and the nonadrenergic agonist angiotensin II (ANG II) in 15 young and 14 older healthy human subjects. Among the old (O) relative to the young (Y) we identified greater plasma NE levels (Y: 1.29 +/- 0.07 nM vs. O: 2.14 +/- 0.17 nM; P = 0.0001); a decrease in NE-mediated reduction in FABF [analysis of variance (ANOVA) P = 0.04]; and, in contrast, no difference in ANG II-mediated reduction in FABF (ANOVA P = 0.43). In the nine older subjects studied during guanadrel (G) to suppress SNS activity, we identified decreased plasma NE levels [placebo (P): 2.11 +/- 0.24 nM vs. G: 1.09 +/- 0.09 nM; P = 0.002], increased NE-mediated FABF response (ANOVA P = 0.01), and no difference in FABF response to ANG II (ANOVA: P = 0.69) compared with P. We conclude that there is appropriate desensitization of arterial alpha-adrenergic responsiveness among the older relative to the young subjects that is specific for the alpha-adrenergic system. Among the older subjects there is homologous upregulation of this response when SNS activity is suppressed.
Effects of sialoadenectomy and exogenous EGF on molar drift and orthodontic tooth movement in rats
Authors: Dolce C. , Anguita J. , Brinkley L. , Karnam P. , Humphreys-Beher M. , Nakagawa Y. , Keeling S. , King G.
Published: December 2017

Effects on bone remodeling have been attributed to epidermal growth factor (EGF). Sialoadenectomy (SX) removes the major source of EGF in rodents and decreases both salivary and serum EGF levels. EGF effects on rat alveolar bone remodeling manifested by molar drift (MD) and orthodontic tooth movement (OTM) were examined using the following two approaches: 1) EGF depletion by SX and replacement by orally administered EGF (50 micrograms.animal-1.day-1); 2) sham rats supplemented with matching amounts of EGF. MD and OTM were measured using cephalometric radiographs; bone formation was measured histomorphometrically using tetracycline labeling. Normal MD was not detected after SX, and alveolar bone formation was significantly reduced both around the tooth and in nondental sites. Replacement EGF given to SX rats and supplemental EGF administered to sham rats changed the direction and enhanced the rate of MD. A mesially directed orthodontic force applied to the molars of SX animals increased bone formation on the distal aspect of the tooth roots. Supplemental EGF did not significantly affect OTM. EGF affects alveolar bone remodeling, as manifested clinically by alterations in normal maxillary MD.
Epinephrine-induced changes in hepatic glucose production after ethanol
Authors: Lang C. H. , Molina P. E. , Skrepnick N. , Bagby G. J. , Spitzer J. J.
Published: December 2017

Previous studies indicate that catecholamines play an important role in mediating the glucose metabolic response to endotoxin. Because acute ethanol (EtOH) intoxication impairs this response, the present study was initiated to ascertain whether EtOH attenuates the lipopolysaccharide response by decreasing the increment in plasma catecholamines after endotoxin or by decreasing the responsiveness of rats to epinephrine. All studies were performed on chronically catheterized fasted rats infused intravenously with either EtOH or an equal volume of saline. In the first series of experiments, intravenous administration of Escherichia coli endotoxin increased, to the same extent, the plasma concentrations of epinephrine and norepinephrine in both saline- and EtOH-infused rats. In the second study, rats were infused with [3-3H]glucose to assess whole body glucose metabolism and the ability of EtOH to alter the glucose metabolic response to epinephrine. The exogenous infusion of a maximally stimulating dose of epinephrine (1 microgram.min-1.kg-1) into saline-infused control animals for 3 h produced a marked hyperglycemia that resulted from a sustained increase in the rate of hepatic glucose production and a reduction in the metabolic clearance rate for glucose. EtOH infusion did not prevent the epinephrine-induced hyperglycemia but blunted the stimulatory effect of epinephrine on glucose production. The differences in glucose metabolism between saline- and EtOH-treated rats could not be explained by changes in plasma insulin or glucagon concentrations. Furthermore, the ability of EtOH to impair the epinephrine-induced increase in glucose production was still evident in rats treated with 4-methylpyrazole, an inhibitor of alcohol dehydrogenase.(ABSTRACT TRUNCATED AT 250 WORDS)
Bidirectional modulation of parathyroid hormone-responsive adenylyl cyclase by protein kinase C
Authors: Kitten A. M. , Hymer T. K. , Katz M. S.
Published: December 2017

The temporal pattern with which phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), modulates parathyroid hormone (PTH)-responsive adenylyl cyclase (AC) was evaluated in a clonal osteoblast-like cell line (UMR-106). Brief (< or = 1 h) exposure of UMR-106 cells to PMA enhanced PTH stimulation of AC, whereas more prolonged PMA treatment decreased the PTH response, with maximum inhibition occurring at < or = 6 h. PMA treatment also resulted in initial activation followed by downregulation of PKC. Exposure of cells to 1,2-dioctanoyl-sn-glycerol, which activated but did not downregulate PKC, resulted in bidirectional modulation of PTH-responsive AC identical to that produced by PMA. Prolonged PMA exposure decreased PTH receptor number, as determined by radioligand binding studies, and reduced PTH receptor mRNA levels, assessed by Northern blot analysis. Forskolin activation of the catalytic subunit of AC was also decreased after prolonged PMA treatment. The results suggest that activation of PKC sequentially stimulates and then inhibits PTH responsiveness. Inhibition of the PTH response occurs by PKC actions exerted on the PTH receptor and the AC catalytic subunit.
Acute adaptation of carbohydrate metabolism to decreased arterial PO2
Authors: Zinker B. A. , Namdaran K. , Wilson R. , Lacy D. B. , Wasserman D. H.
Published: December 2017

To assess the interaction of arterial PO2 (PaO2) and glucose metabolism, conscious 18-h-fasted dogs with chronically implanted sampling catheters (carotid artery, iliac vein) and flow probe (external iliac artery) were studied during inspiration of air containing 21 (n = 9), 14 (n = 6), 11 (n = 4), or 8% (n = 5) O2. Isotopic and arteriovenous methods were used to assess carbohydrate metabolism. PaO2 was 103 +/- 3, 64 +/- 4, 45 +/- 4, and 30 +/- 1 mmHg with decreased inspired O2. Although limb O2 delivery was reduced (51 +/- 6, 42 +/- 8, 39 +/- 7, and 34 +/- 5 ml/min), limb O2 uptake was not compromised. Plasma insulin was 9 +/- 1, 8 +/- 2, 14 +/- 2, and 16 +/- 3 microU/ml, and glucagon was 53 +/- 3, 49 +/- 3, 64 +/- 5, and 101 +/- 7 pg/ml with decreasing O2. Plasma epinephrine and cortisol were increased whereas norepinephrine was unaffected. Glycemia was unaffected by reduced O2, whereas hepatic glucose output (14 +/- 1, 19 +/- 3, 21 +/- 1, and 22 +/- 1 mumol.kg-1.min-1) and glucose disappearance (14 +/- 2, 18 +/- 3, 20 +/- 1, and 22 +/- 2 mumol.kg-1.min-1) rose similarly. Limb glucose uptake (LGU) rose (21.5 +/- 4.7, 21.2 +/- 5.6, 30.6 +/- 4.7, and 45.3 +/- 9.7 mumol/min) with decreasing O2 because of greater fractional extraction (0.023 +/- 0.005, 0.024 +/- 0.005, 0.031 +/- 0.004, and 0.043 +/- 0.004). Of the increased LGU, approximately 33 and 67% were metabolized oxidatively and nonoxidatively.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of IL-1 receptor antagonist and antiserum to TNF-alpha on LPS-induced plasma ACTH and corticosterone rise in rats
Authors: Ebisui O. , Fukata J. , Murakami N. , Kobayashi H. , Segawa H. , Muro S. , Hanaoka I. , Naito Y. , Masui Y. , Ohmoto Y. , et al.
Published: December 2017

Using an antiserum against tumor necrosis factor (TNF)-alpha and an interleukin (IL-1) receptor antagonist, we studied putative roles of these cytokines in mediating the endotoxin-induced elevation of plasma adrenocorticotropic hormone (ACTH) and corticosterone levels in freely moving rats. Intravenous administration of Escherichia coli lipopolysaccharide (LPS) increased plasma ACTH and corticosterone levels in a dose-dependent manner. The plasma corticosterone reached to its highest level among a series of experiments after the administration of even the smallest dose (0.03 microgram/kg) tested. Plasma ACTH and corticosterone levels in these rats were completely inhibited by the intravenous administration of anti-murine TNF-alpha-rabbit antiserum (anti-TNFAS) after the administration of LPS but not by the intravenous administration of IL-1 receptor antagonist (IL-1RA). On the other hand, both recombinant human IL-1RA and anti-TNFAS significantly inhibited plasma ACTH increase stimulated with 10 micrograms/kg LPS. These findings indicate that 1) when the plasma corticosterone increase induced by intravenous LPS remains below its maximum, the effect is exclusively mediated by TNF-alpha, and 2) when a larger amount of LPS is administered, both IL-1 beta and TNF-alpha participate at least in part in the hypothalamic-pituitary-adrenal axis activation.
Phenylarsine oxide inhibits insulin-stimulated protein phosphatase 1 activity and GLUT-4 translocation
Authors: Begum N.
Published: December 2017

Phenylarsine oxide (PAO) has previously been shown to inhibit insulin-stimulated glucose transport without affecting insulin binding and tyrosine kinase activity of insulin receptor (S. C. Frost and M. D. Lane. J. Biol. Chem. 260: 2646-2652, 1985). This study examines the effect of PAO on insulin's ability to activate adipocyte protein phosphatase 1 (PP-1) and dephosphorylate GLUT-4, the insulin-sensitive glucose transporter. In particulate fractions, insulin stimulated PP-1 activity (40% increase over basal with phosphorylase a) in a time- and dose-dependent manner (half-maximal effect of 0.89 nM in 1 min). Insulin did not alter cytosolic PP-1 activity. With GLUT-4 as a substrate, insulin caused more than twofold stimulation of particulate PP-1 activity. Addition of PAO (5 microM) before or after insulin treatment abolished insulin's effect on PP-1 activation. The presence of 2,3-dimercaptopropanol (200 microM) prevented the effect of PAO on PP-1 activation and glucose uptake. In addition, PAO significantly increased GLUT-4 phosphorylation, blocked insulin-stimulated dephosphorylation, and partially diminished insulin-stimulated translocation of GLUT-4. We conclude that PAO may interfere with the components of insulin signal transduction pathways that lead to the activation of PP-1 and this may be responsible for the observed inhibition in insulin action.
Placental and fetal serine fluxes at midgestation in the fetal lamb
Authors: Moores R. R. , Carter B. S. , Meschia G. , Fennessey P. V. , Battaglia F. C.
Published: December 2017

Plasma serine disposal rate (DR), decarboxylation, and conversion to fetal plasma glycine by the placenta were measured in six fetal lambs at 72 +/- 1 days gestation. L-[1-13C]serine, L-[U-14C]serine, and 3H2O were infused over 3 h into the fetal circulation, the latter for measurement of uterine and umbilical blood flow. The fetal plasma serine DR was 8.7 +/- 1.0 mumol/min or 61.8 +/- 4 mumol.min-1.kg fetus-1. Approximately 90% of the DR represented placental uptake of fetal serine. There was no detectable release of fetal serine into the maternal circulation. The fetal arterial plasma glycine-to-serine enrichment ratio was approximately 0.30. The conversion rate of fetal serine to fetal plasma glycine by the placenta was 5.8 +/- 0.7% of the serine DR. Fetal and placental CO2 production from fetal plasma serine carbon was 1.9 +/- 0.4 and 1.2 +/- 0.4 mumol/min, respectively. Thus, at midgestation, there is a rapid fetoplacental serine exchange that constitutes most of the fetal plasma serine turnover. Placental conversion of serine to fetal glycine and serine oxidation together account for only 10% of the placental uptake of fetal serine.
Muscle glyconeogenesis during recovery from a prolonged swim in rats
Authors: Ryan C. , Radziuk J.
Published: December 2017

Glyconeogenesis in muscle was assessed during a 3-h recovery period after prolonged submaximal exercise represented by a 4-h swim. Rats fasted for 12 h and previously catheterized underwent this protocol with the concomitant infusion of [6-3H]glucose and one of the following: 1) [14C]bicarbonate, 2) [U-14C]lactate, and 3) [1-14C]glucose. Rested rats served as controls. The incorporation of 14C label ([14C]bicarbonate and [U-14C]lactate) or its transfer to the sixth position of glucosyl units of glycogen, over and above that taken up from circulating glucose (and determined from [6-3H]glucose uptake), was used as an index of muscle glyconeogenesis. 14C from 14CO2 is not expected to be incorporated into glycogen in muscle, and any incorporation that is not from circulating glucose is used to define experimental error. [14C]lactate incorporation measures equilibration with circulating lactate, and label randomization in glucosyl units beyond that seen in plasma glucose is taken as evidence of glyconeogenesis from locally accumulated glycolytic products. The results of these studies demonstrate 1) no glyconeogenesis in the soleus; 2) in the red and white gastrocnemii, glyconeogenesis takes place only from glycolytic products within the muscle. Approximately 35-40% of the [6-14C]glucose in glycogen can only be accounted for by muscle glyconeogenesis. The substrate does not equilibrate with circulating lactate to a detectable extent. 3) Glyconeogenesis appears to persist throughout the recovery period and uses substrate at the level of pyruvate. This is consistent with a continuing elevation of glycolysis during this period.
Endothelin-1 conversion and receptor characterization in human placental arteries
Authors: Wilkes B. M. , Macica C. M. , Mento P. F.
Published: December 2017

Endothelin-1-(1-21), a potent pressor peptide, is transcribed as big endothelin-(1-38) and converted to active peptide by endothelin-converting enzyme. The current investigation tested the hypothesis that human fetoplacental blood vessels convert big endothelin-1 to active peptide and that fetoplacental blood vessels respond to endothelin-1 by binding of the peptide to specific receptor sites. In the isolated perfused placental cotyledon the addition of big endothelin-1 to the perfusate caused a time-dependent increase in perfusion pressure that corresponded to the appearance of endothelin-1 in the perfusate. The properties of human placental endothelin-1 receptors were defined in binding studies performed on a plasma membrane fraction of small arteries (<1.0 mm) dissected from the placenta. Binding was saturable, reached steady state by 3 h at 25 degrees C, and was linear with protein concentration. Scatchard analysis of binding data indicated a single class of high-affinity binding sites with a dissociation constant of 27.6 +/- 2.3 pM and a density of 856 +/- 119 fmol/mg protein (n = 5). The potency order for competitive inhibition of the binding of 125I-labeled endothelin-1 [endothelin-1 = endothelin-2 > endothelin-3 = sarafotoxin S6b >> big endothelin-1 (human) = big endothelin-1 (porcine)] is most consistent with a type A endothelin receptor subtype. Phenylephrine, bradykinin, norepinephrine, atrial natriuretic factor, diltiazem, U-46619, and angiotensin II did not displace 125I-endothelin-1 binding. Endothelin receptors were shown to have an approximate molecular weight of 36,600 by polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential expression of angiotensin receptor 1A and 1B in mouse
Authors: Burson J. M. , Aguilera G. , Gross K. W. , Sigmund C. D.
Published: December 2017

At least two distinct genes (AT1A and AT1B) encode type 1 angiotensin II (AT1) receptors in rodents. Receptor binding and Northern blot analysis have clearly demonstrated the presence of AT1 receptors and AT1-receptor mRNA in many tissues but fail to differentiate which type 1 receptor subtype is expressed. A reverse-transcriptase polymerase chain reaction restriction fragment length polymorphism (RT-PCR-RFLP) assay was developed to differentiate the expressed mRNA by subtype. Expression of AT1A was clearly evident in kidney, liver, adrenal gland, ovary, brain, testes, adipose tissue, lung, and heart of adult mice. AT1B was absent from most of these tissues but was detectable in brain, testes, and adrenal gland. No significant differences in expression were evident in kidney, liver, brain, lung, or heart from 16.5- or 18.5-gestation-day fetuses, and only AT1A was evident in placenta. Expression of AT1B was confirmed in adrenal gland, brain, and testes, using a primer set that specifically amplifies only AT1B mRNA. Expression of AT1A and AT1B was also examined in As4.1 cells, a renin-expressing mouse kidney tumoral cell line. Receptor binding and competition assays using AT1- and AT2-receptor antagonists revealed that only AT1 receptors are present on the cell surface. Extremely low levels of AT1-receptor mRNA was detected by Northern blot, and RT-PCR-RFLP analysis revealed that only the AT1A subtype is expressed in this cell line. Despite the high homology between the coding sequence of the AT1A and AT1B genes, they exhibit disparate tissue-specific expression profiles.
Effect of insulin on rat heart and skeletal muscle phenylalanyl-tRNA labeling and protein synthesis in vivo
Authors: Young L. H. , Stirewalt W. , McNulty P. H. , Revkin J. H. , Barrett E. J.
Published: December 2017

In vivo measurement of muscle protein synthesis and its hormonal regulation is limited by the difficulty of measuring aminoacyl-tRNA specific activity (SA). We assessed the kinetics of heart and skeletal muscle phenylalanyl-tRNA labeling during continuous infusion of L-[ring-2,6-3H]phenylalanine (Phe) to fasted anesthetized rats. We measured Phe SA in arterial and femoral venous plasma, the tissue acid-soluble pool and muscle protein hydrolysates after 5 min (n = 7), 30 min (n = 6), and 90 min (n = 7). We also assessed insulin's effect on labeling of the tRNA pool and muscle protein synthesis during a hyperinsulinemic clamp (2 mU.kg-1.min-1; n = 7). Labeling of tRNA in heart reached 59 +/- 5, 67 +/- 3, and 83 +/- 3% of arterial SA at 5, 30, and 90 min of saline infusion, respectively, but only 10 +/- 5, 34 +/- 2, and 48 +/- 2% in skeletal muscle at those times (P < 0.01 vs. heart). The tRNA SA was intermediate between SA in the acid-soluble pool and arterial plasma. Femoral venous SA was 32 +/- 2% lower (P < 0.001) than arterial SA. Skeletal muscle tRNA SA was also 29 +/- 3% lower (P < 0.001) than femoral venous SA. Insulin did not alter tRNA labeling and neither heart (9.8 +/- 1.1%/day for saline vs. 8.4 +/- 1.0%/day for insulin) nor skeletal muscle (6.7 +/- 1.5%/day vs. 4.2 +/- 0.4%/day) protein synthesis. Thus labeling of phenylalanyl-tRNA occurs more rapidly in heart than in skeletal muscle and is unaffected by insulin.(ABSTRACT TRUNCATED AT 250 WORDS)
Anabolic effects of the beta 2-adrenoceptor agonist salmeterol are dependent on route of administration
Authors: Moore N. G. , Pegg G. G. , Sillence M. N.
Published: December 2017

It is reported that a long duration of action is required for beta 2-adrenoceptor agonists to evoke an anabolic response. In the present study, we compare the potency of clenbuterol with that of the new long-acting compound salmeterol, when given at equimolar doses to female Wistar rats by different routes of administration. Given orally for 10 days, salmeterol had no effect on growth at a dose of 120 micrograms/day, whereas at 2.4 mg/day the drug caused significant increases in body and carcass weight and in the mass of the mixed-fiber gastrocnemius/plantaris and tibialis anterior muscles, but there were no increases in the slow-twitch soleus muscles. A similar growth response was seen when clenbuterol was given orally at a dose of only 97 micrograms/day, with an additional response seen in soleus muscle at 1.9 mg/day. Thus clenbuterol was more potent than salmeterol when given by this route of administration. When the drugs were infused by osmotic minipump, both salmeterol (130 micrograms/day) and clenbuterol (100 micrograms/day) caused increases in body weight gain and in the weights of the mixed-fiber muscles, with the most dramatic effect of infusion being to greatly increase the anabolic effect of salmeterol in soleus muscle. A single intraperitoneal injection of salmeterol (53 micrograms) or clenbuterol (40 micrograms) caused a similar rapid increase in the concentration of adenosine 3',5'-cyclic monophosphate in gastrocnemius muscle. These results indicate that the potency of salmeterol in vivo is dependent on its route of administration and that slow-twitch muscles are less sensitive than mixed-fiber muscles to the anabolic effects of beta 2-adrenoceptor agonists.
Insulinotropic action of glutamic acid dimethyl ester
Authors: Sener A. , Conget I. , Rasschaert J. , Leclercq-Meyer V. , Villanueva-Penacarrillo M. L. , Valverde I. , Malaisse W. J.
Published: December 2017

Glutamic acid dimethyl ester (GME; 3.0–10.0 mM) enhanced insulin release evoked by 6.0–8.3 mM D-glucose, 1.0–10.0 mM L-leucine, or 5.0–10.0 mM 2-amino-bicyclo(2,2,1)heptane-2-carboxylic acid, causing a shift to the left of the sigmoidal relationship between insulin output and D-glucose concentration. In the absence of D-glucose, GME also unmasked the insulinotropic potential of glibenclamide. In islets exposed to L-leucine, the insulinotropic action of GME coincided with an early fall and later increase in 86Rb outflow and augmentation of 45Ca outflow from prelabeled islets. The measurement of O2 uptake, NH4+ output, production of 14CO2 from islets prelabeled with [U-14C]palmitate, generation of 14C-labeled amino acids and 14CO2 from the dimethyl ester of either L-[1-14C]glutamic acid or L-[U-14C]glutamic acid, and D-[2-14C]glucose as well as D-[6-14C]glucose oxidation in the presence or absence of GME indicated that the latter ester was efficiently converted to L-glutamate and its further metabolites. The overall gain in O2 uptake represented the balance between GME oxidation and its sparing action on the catabolism of endogenous fatty acids and exogenous D-glucose. It is proposed that GME might represent a new tool to bypass beta-cell defects in D-glucose transport, phosphorylation, and further metabolism and, hence, to stimulate insulin release in experiments conducted in animal models of non-insulin-dependent diabetes mellitus.
Postprandial myofibrillar and whole body protein synthesis in young and old human subjects
Authors: Welle S. , Thornton C. , Statt M. , McHenry B.
Published: December 2017

Rates of incorporation of leucine (using L-[1-13C]leucine as a tracer) into myofibrillar and whole body proteins were determined in healthy old (> 60 yr old, n = 7) and young (< 30 yr old, n = 9) men and women who were fed small meals (4% of daily energy) every 30 min. There was no difference in whole body incorporation of leucine into proteins in the young (148 +/- 5 mumol.h-1.kg lean body mass-1, means +/- SE) and old groups (150 +/- 3 mumol.h-1.kg lean body mass-1). However, the fractional myofibrillar protein synthesis in the vastus lateralis muscle was 28% slower in the older group (0.063 +/- 0.004 vs. 0.088 +/- 0.003 %/h, P < 0.001). Extrapolation of these results to whole body myofibrillar synthesis (fractional rate x myofibrillar mass estimated by creatinine excretion) indicated that, in the older group, total myofibrillar synthesis was 43% slower (1.8 +/- 0.2 vs. 3.1 +/- 0.2 g/h, P < 0.01) and that their myofibrillar synthesis was a smaller portion of whole body protein synthesis (15 +/- 1 vs. 23 +/- 1%, P < 0.001). Compared with age-matched postabsorptive subjects, whole body protein synthesis was approximately 25% faster, and fractional myofibrillar synthesis was approximately 50% faster in these fed subjects, both young and old. We conclude that myofibrillar synthesis is slower in older subjects during both postabsorptive and postprandial conditions but that aging does not impair the stimulatory effect of feeding on protein synthesis.
Expression of components of the RAS during prolonged blockade at different levels in primates
Authors: Samani N. J. , Cumin F. , Kelly M. , Wood J. M.
Published: December 2017

To assess the effects of inhibition of the renin-angiotensin system at different levels on plasma concentrations of components of the system and on renin and angiotensinogen gene expression, marmosets on a low-sodium diet were treated for 1 wk by continuous intraperitoneal infusion with either the renin inhibitor CGP-29287, the ACE inhibitor benazeprilat, the angiotensin II antagonist valsartan, the renin inhibitory monoclonal antibody R-3-36-16, or vehicle. Plasma total immunoreactive renin increased (14- to 20-fold) after all three modes of interference. Plasma angiotensinogen was significantly reduced in the benazeprilat- and valsartan-treated marmosets but not in the CGP-29287-treated animals. Plasma concentration of angiotensin II was significantly decreased in the benazeprilat-, CGP-29287-, and R-3-36-16-treated marmosets and was increased in the valsartan-treated marmosets. Kidney renin mRNA level increased 8- to 15-fold in all groups. Hepatic angiotensinogen mRNA level increased with CGP-29287 treatment but decreased with the other treatments. Kidney angiotensinogen mRNA level was not affected by any treatment. Different modes of inhibition of the renin-angiotensin system have different effects on plasma components of the system and liver angiotensinogen expression.
Role of norepinephrine in hepatic gluconeogenesis: evidence of aging and training effects
Authors: Podolin D. A. , Gleeson T. T. , Mazzeo R. S.
Published: December 2017

This study examined the relationship among the sympathetic neurotransmitter norepinephrine (NE), hepatic gluconeogenesis, and glyconeogenesis in 63 (30 trained and 33 untrained) young (7 mo), middle-aged (15 mo), and old (25 mo) male Fischer 344 rats. Animals were trained 1 h/day, 5 days/wk for 10 wk at treadmill speeds of 75% of age-specific maximal capacity. Liver sections, removed at rest, were sliced and incubated in [14C]lactic acid and 0, 0.5, 1.0, 3.0, or 6.0 ng/ml NE. The rate of [14C]lactate incorporation into glucose was significantly greater in young compared with old animals in both training groups and at all NE concentrations. All trained animals had greater rates of glucose production from lactate than their untrained counterparts at 0.5, 1.0, 3.0, and 6.0 ng/ml NE. At each NE concentration, the old rats showed the lowest rates of glycogen synthesis from lactate. The untrained rats in all age groups were the least responsive to increases in NE concentration. Total hepatic glycogen synthase activity exhibited age-related declines as the young and middle-aged had significantly greater total activity compared with the old animals: 620.4 +/- 27.5, 590.0 +/- 37.9, and 436.3 +/- 44.5 disintegrations/min, respectively. No differences with training were found in total activity. The percent of glycogen synthase in the active form was significantly greater in young compared with old in both the trained (48.6 +/- 2.0 vs. 40.0 +/- 1.3% active) and untrained animals (44.7 +/- 2.2 vs. 35.4 +/- 1.5% active).(ABSTRACT TRUNCATED AT 250 WORDS)
Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise
Authors: MacLean D. A. , Graham T. E. , Saltin B.
Published: December 2017

In this study, five men exercised the knee extensor muscles of one leg for 60 min (71 +/- 2% maximal work capacity) with and without (control) an oral supplement (77 mg/kg) of branched-chain amino acids (BCAA). BCAA supplementation resulted in a doubling (P <0.05) of the arterial BCAA levels before exercise (339 +/- 15 vs. 822 +/- 86 microM). During the 60 min of exercise, the total release of BCAA was 68 +/- 93 vs. 816 +/- 198 mumol/kg (P < 0.05) for the BCAA and control trials, respectively. The intramuscular BCAA concentrations were higher (P < 0.05) for the BCAA trial and remained higher (P < 0.05) throughout exercise. In both trials, substantial quantities of NH3 were released, and when NH3 production equivalent to IMP accumulation was subtracted the net NH3 production was 1,112 +/- 279 and 1,670 +/- 245 mumol/kg (P < 0.05) for the control and BCAA trials, respectively. In contrast, the release of the essential amino acids (EAA) was much lower for the BCAA than the control trial (P < 0.05). When the BCAA were subtracted from the EAA (EAA-BCAA), the total release of EAA minus BCAA was lower (P < 0.05) for the BCAA (531 +/- 70 mumol/kg) than the control (924 +/- 148 mumol/kg) trial. These data suggest that BCAA supplementation results in significantly greater muscle NH3 production during exercise. Furthermore, the increased intramuscular and arterial BCAA levels before and during exercise result in a suppression of endogenous muscle protein breakdown during exercise.
Ontogeny of the two angiotensin II type 1 receptor subtypes in rats
Authors: Shanmugam S. , Corvol P. , Gasc J. M.
Published: December 2017

The two subtypes (AT1A and AT1B) of the type 1 (AT1) angiotensin II receptor mRNA were localized by in situ hybridization in rat fetal tissues from day 11 to 19 of gestation and in the young rat from day 0 to 10 postpartum, by use of 35S-labeled cRNA probes. Both subtype mRNAs were present in the kidney and in the adrenal gland. Organs such as liver, lung, heart, and undifferentiated mesenchymes expressed only AT1A mRNA. In contrast to the adult, only AT1A subtype was expressed during fetal and postnatal periods in the pituitary gland. Large blood vessels (e.g., aorta and cerebral arteries) expressed exclusively AT1A mRNA during fetal stages. The expression of each subtype appears to be differentially regulated, in a tissue- and age-specific way. This spatotemporal regulation of AT1A and AT1B expression suggests that angiotensin II could act as a differentiation factor during organogenesis in addition to its classical role as a regulator of the cardiovascular system.