bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of protein intake and physical activity on 24-h pattern and rate of macronutrient utilization
Authors: Forslund Anders H. , El-Khoury Antoine E. , Olsson Roger M. , Sjödin Anders M. , Hambraeus Leif , Young Vernon R.
Published: December 2017

Effects of moderate physical activity (90 min at 45–50% of maximal O2 uptake 2 times daily) and “high” (2.5 g protein ⋅ kg−1 ⋅ day−1, n = 6) or “normal” protein intake (1.0 g protein ⋅ kg−1 ⋅ day−1, n = 8) on the pattern and rate of 24-h macronutrient utilization in healthy adult men were compared after a diet-exercise-adjustment period of 6 days. Energy turnover (ET) was determined by indirect and direct (suit) calorimetry, and “protein oxidation” was determined by a 24-h continuous intravenous infusion of [1-13C]leucine. Subjects were in slight positive energy balance during both studies. Protein contributed to a higher (22 vs. 10%) and carbohydrate (CHO) a lower (33 vs. 58%) proportion of total 24-h ET on the high- vs. normal-protein intake. The highest contribution of fat to ET was seen postexercise during fasting (73 and 61% of ET for high and normal, respectively). With the high-protein diet the subjects were in a positive protein ( P < 0.001) and CHO balance ( P < 0.05) and a negative fat balance ( P < 0.05). The increased ET postexercise was not explained by increased rates of urea production and/or protein synthesis.
Neuronal actions of oxytocin on the subfornical organ of male rats
Authors: Hosono Takayoshi , Schmid Herbert A. , Kanosue Kazuyuki , Simon Eckhart
Published: December 2017

The aim of this study was to investigate effects of oxytocin (OT) on electrical neuronal activities in rat subfornical organ (SFO) and compare its action with the well-described excitatory effects of blood-borne angiotensin II (ANG II) on the same SFO neurons. With the use of extracellular recordings from spontaneously active neurons in slice preparations of the SFO of male rats, 11.7% of tested neurons ( n = 206) were excited and 9.7% were inhibited by superfusion with 10−6 M OT. Both excitatory and inhibitory effects of OT were dose dependent with similar threshold concentrations and were blocked by a specific OT-receptor antagonist but not by a vasopressin receptor antagonist. Blocking synaptic transmission with low calcium medium suppressed only inhibitory effects of OT. All but one of the OT-sensitive neurons were also excited by superfusion with ANG II at a concentration much lower than required for OT, suggesting that synaptically released OT rather than blood-borne OT alters the activity of SFO neurons in vivo. The results support the hypothesis that neurally released OT may modulate SFO-mediated functions by acting on OT-sensitive neurons.
Effect of GIP and GLP-1 antagonists on insulin release in the rat
Authors: Tseng Chi-Chuan , Zhang Xiao-Ying , Wolfe M. Michael
Published: December 2017

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are potent insulinotropic peptides released from the small intestine. To examine their relative contribution to postprandial insulin release, a specific GIP antagonist (ANTGIP) and a GLP-1 antagonist, exendin-(9—39)-NH2, were infused into rats after an intragastric glucose meal. In control rats, plasma glucose and insulin levels rose gradually during the first 20 min and then decreased. Exendin-(9—39)-NH2 administration inhibited postprandial insulin secretion by 32% at 20 min and concomitantly increased plasma glucose concentrations. In contrast, ANTGIP treatment not only induced a 54% decrease in insulin secretion but also a 15% reduction in plasma glucose levels 20 min after the glucose meal. In vivo studies in rats demonstrated that glucose uptake in the upper small intestine was significantly inhibited by the ANTGIP, an effect that might account for the decrease in plasma glucose levels observed in ANTGIP-treated rats. When the two antagonists were administered to rats concomitantly, no potentiating effect on either insulin release or plasma glucose concentration was detected. Glucose meal-stimulated GLP-1 release was not affected by ANTGIP administration, whereas postprandial glucagon levels were diminished in rats receiving exendin-(9—39)-NH2. The results of these studies suggest that GIP and GLP-1 may share a common mechanism in stimulating pancreatic insulin release. Furthermore, the GIP receptor appears to play a role in facilitating glucose uptake in the small intestine.
Glucose production during strenuous exercise in humans: role of epinephrine
Authors: Howlett Kirsten , Febbraio Mark , Hargreaves Mark
Published: December 2017

The increase in hepatic glucose production (HGP) that occurs during intense exercise is accompanied by a simultaneous increase in epinephrine, which suggests that epinephrine may be important in regulating HGP. To further investigate this, six trained men were studied twice. The first trial [control (Con)] consisted of 20 min of cycling at 40 ± 1% peak oxygen uptake (V˙o 2 peak) followed by 20 min at 80 ± 2%V˙o 2 peak. During the second trial [epinephrine (Epi)], subjects exercised for 40 min at 41 ± 2%V˙o 2 peak. Epinephrine was infused during the latter 20 min of exercise and resulted in plasma levels similar to those measured during intense exercise in Con. Glucose kinetics were measured using a primed, continuous infusion of [3-3H]glucose. HGP was similar at rest (Con, 11.0 ± 0.5 and Epi, 11.1 ± 0.5 μmol ⋅ kg−1 ⋅ min−1). In Con, HGP increased ( P < 0.05) during exercise to 41.0 ± 5.2 μmol ⋅ kg−1 ⋅ min−1at 40 min. In Epi, HGP was similar to Con during the first 20 min of exercise. Epinephrine infusion increased ( P < 0.05) HGP to 24.0 ± 2.5 μmol ⋅ kg−1 ⋅ min−1at 40 min, although this was less ( P< 0.05) than the value in Con. The results suggest that epinephrine can increase HGP during exercise in trained men; however, epinephrine during intense exercise cannot fully account for the rise in HGP. Other glucoregulatory factors must contribute to the increase in HGP during intense exercise.
AMP-activated protein kinase, a metabolic master switch: possible roles in Type 2 diabetes
Authors: Winder W. W. , Hardie D. G.
Published: December 2017

Adenosine 5′-monophosphate-activated protein kinase (AMPK) now appears to be a metabolic master switch, phosphorylating key target proteins that control flux through metabolic pathways of hepatic ketogenesis, cholesterol synthesis, lipogenesis, and triglyceride synthesis, adipocyte lipolysis, and skeletal muscle fatty acid oxidation. Recent evidence also implicates AMPK as being responsible for mediating the stimulation of glucose uptake induced by muscle contraction. In addition, the secretion of insulin by insulin secreting (INS-1) cells in culture is modulated by AMPK activation. The net effect of AMPK activation is stimulation of hepatic fatty acid oxidation and ketogenesis, inhibition of cholesterol synthesis, lipogenesis, and triglyceride synthesis, inhibition of adipocyte lipolysis and lipogenesis, stimulation of skeletal muscle fatty acid oxidation and muscle glucose uptake, and modulation of insulin secretion by pancreatic β-cells. In skeletal muscle, AMPK is activated by contraction. Type 2 diabetes mellitus is likely to be a disease of numerous etiologies. However, defects or disuse (due to a sedentary lifestyle) of the AMPK signaling system would be predicted to result in many of the metabolic perturbations observed in Type 2 diabetes mellitus. Increased recruitment of the AMPK signaling system, either by exercise or pharmaceutical activators, may be effective in correcting insulin resistance in patients with forms of impaired glucose tolerance and Type 2 diabetes resulting from defects in the insulin signaling cascade.
Aminoacyl-tRNA and tissue free amino acid pools are equilibrated after a flooding dose of phenylalanine
Authors: Davis Teresa A. , Fiorotto Marta L. , Nguyen Hanh V. , Burrin Douglas G.
Published: December 2017

The flooding dose method, which is used to measure tissue protein synthesis, assumes equilibration of the isotopic labeling between the aminoacyl-tRNA pool and the tissue and blood free amino acid pools. However, this has not been verified for a phenylalanine tracer in an in vivo study. We determined the specific radioactivity of [3H]phenylalanine in the aminoacyl-tRNA and the tissue and blood free amino acid pools of skeletal muscle and liver 30 min after administration of a flooding dose of phenylalanine along with [3H]phenylalanine. Studies were performed in neonatal pigs in the fasted and refed states and during hyperinsulinemic-euglycemic-amino acid clamps. The results showed that, 30 min after the administration of a flooding dose of phenylalanine, there was equilibration of the specific radioactivity of phenylalanine among the blood, tissue, and tRNA precursor pools. Equilibration of the specific radioactivity of the three precursor pools for protein synthesis occurred in both skeletal muscle and liver. Neither feeding nor insulin status affected the aminoacyl-tRNA specific radioactivity relative to the tissue free amino acid specific radioactivity. The results support the assumption that the tissue free amino acid pool specific radioactivity is a valid measure of the precursor pool specific radioactivity and thus can be used to calculate protein synthesis rates in skeletal muscle and liver when a flooding dose of phenylalanine is administered.
Inhibition of salmon calcitonin on secretion of progesterone and GnRH-stimulated pituitary luteinizing hormone
Authors: Tsai Shiow-Chwen , Lu Chien-Chen , Chen Jiann-Jong , Chiao Yu-Chung , Wang Shyi-Wu , Hwang Jiuan-Jiuan , Wang Paulus S.
Published: December 2017

The effects of salmon calcitonin (sCT) on the production of progesterone and secretion of luteinizing hormone (LH) were examined in female rats. Diestrous rats were intravenously injected with saline, sCT, human chorionic gonadotropin (hCG), or hCG plus sCT. Ovariectomized (Ovx) rats were injected with saline or sCT. In the in vitro experiments, granulosa cells and anterior pituitary glands (APs) were incubated with the tested drugs. Plasma LH levels of Ovx rats were reduced by sCT injection. Administration of sCT decreased the basal and hCG-stimulated progesterone release in vivo and in vitro. 8-Bromo-cAMP dose dependently increased progesterone production but did not alter the inhibitory effect of sCT. H-89 did not potentiate the inhibitory effect of sCT. Higher doses of 25-hydroxycholesterol and pregnenolone stimulated progesterone production and diminished the inhibitory effects of sCT. sCT did not decrease basal release of LH by APs, but pretreatment of sCT decreased gonadotropin-releasing hormone (GnRH)-stimulated LH secretion. These results suggested that sCT inhibits progesterone production in rats by preventing the stimulatory effect of GnRH on LH release in rat APs and acting directly on ovarian granulosa cells to decrease the activities of post-cAMP pathway and steroidogenic enzymes.
Increased insulin secretion and normalization of glucose tolerance by cholinergic agonism in high fat-fed mice
Authors: Ahrén Bo , Sauerberg Per , Thomsen Christian
Published: December 2017

Increased insulinotropic activity by the cholinergic agonist carbachol exists in insulin-resistant high fat-fed C57BL/6J mice. We examined the efficiency and potency of carbachol to potentiate glucose-stimulated insulin secretion and to improve glucose tolerance in these animals. Intravenous administration of carbachol (at 15 and 50 nmol/kg) markedly potentiated glucose (1 g/kg)-stimulated insulin secretion in mice fed both a control and a high-fat diet (for 12 wk), with a higher relative potentiation in high fat-fed mice measured as increased (1–5 min) acute insulin response and area under the 50-min insulin curve. Concomitantly, glucose tolerance was improved by carbachol. In fact, carbachol normalized glucose-stimulated insulin secretion and glucose tolerance in mice subjected to a high-fat diet. Carbachol (>100 nmol/l) also potentiated glucose-stimulated insulin secretion from isolated islets with higher efficiency in high fat-fed mice. In contrast, binding of the muscarinic receptor antagonist [ N- methyl-3H]scopolamine to islet muscarinic receptors and the contractile action of carbachol on ileum muscle strips were not different between the two groups. We conclude that carbachol normalizes glucose tolerance in insulin resistance.
Recycling of glucose and determination of the Cori Cycle and gluconeogenesis
Authors: Katz Joseph , Tayek John A.
Published: December 2017

We have derived equations, by employing [U-13C]glucose and mass isotopomer analysis, to determine the pathways of glycogen synthesis (J. Katz, W. P. Lee, P. A. Wals, and E. A. Bergner. J. Biol. Chem. 264: 12994–13004, 1989). More recently, by use of these methods we have derived equations to determine the rate of glucose recycling and of gluconeogenesis [Tayek and Katz. Am. J. Physiol.270 ( Endocrinol. Metab. 33): E709–E717, 1996 and 272 ( Endocrinol. Metab. 35): E476–E484, 1997, and Katz and Tayek. Am. J. Physiol. 275 ( Endocrinol. Metab. 38): E537–E542, 1988]. The former equations have been criticized and challenged by C. Des Rosiers, B. R. Landau, and H. Brunengraber [ Am. J. Physiol. 259 ( Endocrinol. Metab. 22): E757–E762, 1990], and the latter recently by B. R. Landau, J. Wahren, S. F. Previs, G. K. Ekberg, D. Yang, and H. Brunengraber [ Am. J. Physiol. 274 ( Endocrinol. Metab. 37): E954–E961, 1998]. Landau et al. claimed that our equations were in error and “corrected” them. Their analysis, and their values for recycling and gluconeogenesis (GNG) differ markedly from ours. We show here our equations and estimates of recycling and GNG to be correct. We present here a theoretical analysis of recycling and discuss the determination of the Cori Cycle and GNG. We illustrate by numerical examples the difference in parameters of glucose metabolism calculated by the methods of Katz and Landau. J. Radziuk and W. N. P. Lee [ Am. J. Physiol. 277 ( Endocrinol Metab. 40): E199–E207, 1999] and J. K. Kelleher [ Am. J. Physiol. 277 ( Endocrinol. Metab. 40): E395–E400, 1999] present a mathematical analysis that, although differing in some respects from Landau’s, supports his equation for GNG. We show in theappendix that their derivation of the equation for GNG is incorrect.
Sparing effect of leptin on liver glycogen stores in rats during the fed-to-fasted transition
Authors: O’Doherty Robert M. , Anderson Paul R. , Zhao Allan Z. , Bornfeldt Karin E. , Newgard Christopher B.
Published: December 2017

The effect of moderate hyperleptinemia (∼20 ng/ml) on liver and skeletal muscle glycogen metabolism was examined in Wistar rats. Animals were studied ∼90 h after receiving recombinant adenoviruses encoding rat leptin (AdCMV-leptin) or β-galactosidase (AdCMV-βGal). Liver and skeletal muscle glycogen levels in the fed and fasted (18 h) states were similar in AdCMV-leptin- and AdCMV-βGal-treated rats. However, after delivery of a glucose bolus, liver glycogen levels were significantly greater in AdCMV-leptin compared with AdCMV-βGal rats ( P < 0.05). To investigate the mechanism(s) of these differences, glycogen levels were measured immediately after the cessation of a 3- or 6-h glucose infusion or 3, 6, and 9 h after the cessation of a 6-h glucose infusion. Similar increases in liver and skeletal muscle glycogen occurred in hyperleptinemic and control rats in response to glucose infusions. However, 3 and 6 h after the cessation of a glucose infusion, liver glycogen levels were approximately twofold greater ( P < 0.05) in AdCMV-leptin-treated compared with AdCMV-βGal-treated animals. Skeletal muscle glycogen levels were similar in AdCMV-leptin-treated and AdCMV-βGal-treated animals at the same time points. Glycogen phosphorylase, phosphodiesterase 3B, and glycogen synthase activities were unaltered by hyperleptinemia. We conclude that moderate increases in plasma leptin levels decrease liver glycogen degradation during the fed-to-fasted transition.
GLUT-4myc ectopic expression in L6 myoblasts generates a GLUT-4-specific pool conferring insulin sensitivity
Authors: Ueyama Atsunori , Yaworsky Karen L. , Wang Qinghua , Ebina Yousuke , Klip Amira
Published: December 2017

Insulin stimulates glucose uptake into muscle and fat cells via recruitment of the glucose transporter 4 (GLUT-4) from intracellular store(s) to the cell surface. Robust stimulation of glucose uptake by insulin coincides with the expression of GLUT-4 during differentiation of muscle and fat cells, but it is not known if GLUT-4 expression suffices to confer insulin sensitivity to glucose uptake. We have therefore examined the effect of expression of a myc epitope-tagged GLUT-4 (GLUT-4myc) into L6 myoblasts, which do not express endogenous GLUT-4 until differentiated into myotubes. Ectopic expression of GLUT-4myc markedly improved insulin sensitivity of glucose uptake in L6 myoblasts. The GLUT-4myc protein distributed equally to the cell surface and intracellular compartments in myoblasts, and the intracellular fraction of GLUT-4myc further increased in myotubes. In myoblasts, the intracellular GLUT-4myc compartment contained the majority of the insulin-regulatable amino peptidase (IRAP) but less than half of the GLUT-1, suggesting segregation of GLUT-4myc and IRAP to a specific cellular locus. Insulin stimulation of phosphatidylinositol 3-kinase and protein kinase B-α activities was similar for L6-GLUT-4myc myoblasts and myotubes. At both stages, GLUT-4myc responded to insulin by translocating to the cell surface. These results suggest that GLUT-4myc segregates into a specific compartment in L6 myoblasts and confers insulin sensitivity to these cells. L6-GLUT-4myc myoblasts, which are easily transfectable with various constructs, are a useful resource to study insulin action.
Inhibition of liver protein synthesis during laparoscopic surgery
Authors: Barle Hans , Nyberg Björn , Ramel Stig , Essén Pia , McNurlan Margaret A. , Wernerman Jan , Garlick Peter J.
Published: December 2017

Previous studies have indicated that laparoscopic surgery is associated with a decline in liver protein synthesis. In this study, the fractional synthesis rate (FSR) of total liver protein and albumin was measured in patients undergoing elective laparoscopic cholecystectomy at different times after commencing the procedure ( n = 8 + 8). Liver biopsy specimens were taken after 15 min of surgery in an “early” group and after 49 min of surgery in a “late” group. The liver FSR was higher in the early group (24.1 ± 4.7%/day) compared with the late group (19.0 ± 2.8%/day, P < 0.02). The fractional and absolute synthesis rates of albumin were similar in the two groups, 6.4 ± 1.5 vs. 6.5 ± 1.0%/day and 97 ± 19 vs. 96 ± 18 mg ⋅ kg−1⋅ day−1for the early and late groups, respectively. It is concluded that laparoscopic surgery was accompanied by a decrease in total liver protein synthesis rate, which developed rapidly during surgery. In contrast, no change in the synthesis rate of albumin was apparent during the course of surgery.
Renin in thymus, gut, hindlimb, and adrenal of (mRen-2)27 and normal rats: secretion and content studies
Authors: Rong Pei , Wilkinson-Berka Jennifer L. , Skinner Sandford L.
Published: December 2017

Thymic ablation and assay of organ renin revealed that one-third of the increasing plasma level of active renin after removal of kidneys and adrenals from Ren-2 rats originates from the thymus. Splanchnic arteriovenous difference and renin content indicate that gut can account for the remainder. Secretion of active renin from these sites correlated significantly with increasing plasma potassium. Prorenin was not secreted from these sites or from hindlimb in amounts sufficient to raise the plasma level, and yet plasma prorenin remained higher than active renin throughout the 12-h protocol. The source of prorenin that accounts for the high plasma prorenin phenotype of the intact conscious Ren-2 rat was not specifically identified. When sensitive assays were used, a low level of active renin secretion from thymus and gut was also apparent 12 h after removal of kidneys and adrenals in normal Sprague-Dawley rats, and plasma prorenin was at this time higher than active renin. A likely source of this extrarenal, extra-adrenal renin is the macrophage.
Differential regulation of MAP kinase by contraction and insulin in skeletal muscle: metabolic implications
Authors: Wojtaszewski Jørgen F. P. , Lynge Jan , Jakobsen Allan B. , Goodyear Laurie J. , Richter Erik A.
Published: December 2017

We have investigated the activation of the extracellular signal-regulated kinases (ERK1 and ERK2) by muscle contraction and insulin in perfused rat skeletal muscle. Both stimuli activated ERK1 and ERK2 by an upstream kinase MAP/ERK kinase (MEK)-dependent mechanism, as the MEK inhibitor PD-98059 inhibited ERK phosphorylation. The presence of the phosphatidylinositol (PI) 3-kinase inhibitors LY-294002 and wortmannin totally eradicated ERK1 and ERK2 phosphorylation in response to insulin but not contraction. Insulin and muscle contraction activated muscle glucose transport, glycogen synthase, and amino acid transport independently of ERK signaling, whereas the PI 3-kinase inhibitors abolished the stimulatory effects of insulin but not those of contraction on these three cellular processes. We conclude that 1) insulin and contraction activate ERK signaling in skeletal muscle; 2) ERK signaling is not necessary for activation of glucose and amino acid transport or glycogen synthase activity by contraction and insulin in skeletal muscle; and 3) insulin-induced activation of MEK, the upstream activator of ERK, is dependent on PI 3-kinase, whereas contraction utilizes a different mechanism.
Effect of fasting on the intracellular metabolic partition of intravenously infused glucose in humans
Authors: Fery F. , Plat L. , Balasse E. O.
Published: December 2017

The effects of fasting on the pathways of insulin-stimulated glucose disposal were explored in three groups of seven normal subjects. Group 1 was submitted to a euglycemic hyperinsulinemic clamp (∼100 μU/ml) after both a 12-h and a 4-day fast. The combined use of [3-3H]- and [U-14C]glucose allowed us to demonstrate that fasting inhibits, by ∼50%, glucose disposal, glycolysis, glucose oxidation, and glycogen synthesis via the direct pathway. In group 2, in which the clamp glucose disposal during fasting was restored by hyperglycemia (155 ± 15 mg/dl), fasting stimulated glycogen synthesis (+29 ± 2%) and inhibited glycolysis (−32 ± 3%) but only in its oxidative component (−40 ± 3%). Results were similar in group 3 in which the clamp glucose disposal was restored by a pharmacological elevation of insulin (∼2,800 μU/ml), but in this case, both glycogen synthesis and nonoxidative glycolysis participated in the rise in nonoxidative glucose disposal. In all groups, the reduction in total carbohydrate oxidation (indirect calorimetry) induced by fasting markedly exceeded the reduction in circulating glucose oxidation, suggesting that fasting also inhibits intracellular glycogen oxidation. Thus prior fasting favors glycogen retention by three mechanisms: 1) stimulation of glycogen synthesis via the direct pathway; 2) preferential inhibition of oxidative rather than nonoxidative glycolysis, thus allowing carbon conservation for glycogen synthesis via the indirect pathway; and 3) suppression of intracellular glycogen oxidation.
Role of AT1 receptors and autonomic nervous system in mediating acute pressor responses to ANG II in anesthetized mice
Authors: Bivalacqua Trinity J. , Dalal Ajay , Champion Hunter C. , Kadowitz Philip J.
Published: December 2017

Hemodynamic responses to angiotensin II and the role of AT1 and AT2 receptors and the autonomic nervous system in mediating acute responses to angiotensin II were investigated in anesthetized CD1 mice. Injections of angiotensin II caused dose-related increases in systemic arterial pressure that were antagonized by candesartan. Pressor responses to angiotensin II were not altered by PD-123,319 in doses up to 25 mg/kg iv. At the lowest dose studied (20 μg/kg iv), the inhibitory effects of candesartan were competitive, whereas at the highest dose (100 μg/kg iv) the dose-response curve for angiotensin II was shifted to the right in a nonparallel manner with inhibitory effects that could not be surmounted. The inhibitory effects of candesartan were selective and were similar in animals pretreated with enalaprilat (1 mg/kg iv) to reduce endogenous angiotensin II production. Acute pressor responses to angiotensin II were not altered by propranolol (200 μg/kg iv), phentolamine (200 μg/kg iv), or atropine (1 mg/kg iv) but were enhanced by hexamethonium (5 mg/kg iv). Increases in total peripheral resistance induced by angiotensin II were inhibited by the AT1-receptor antagonist but were not altered by AT2-, α-, or β-receptor antagonists. These results suggest that acute pressor responses to angiotensin II are mediated by AT1 receptors, are buffered by the baroreceptors, and are not modulated by effects on AT2 receptors and that activation of the sympathetic nervous system plays little if any role in mediating rapid hemodynamic responses to the peptide in anesthetized CD1 mice.
Skeletal muscle fatty acid metabolism in association with insulin resistance, obesity, and weight loss
Authors: Kelley David E. , Goodpaster Bret , Wing Rena R. , Simoneau Jean-Aime
Published: December 2017

The current study was undertaken to investigate fatty acid metabolism by skeletal muscle to examine potential mechanisms that could lead to increased muscle triglyceride in obesity. Sixteen lean and 40 obese research volunteers had leg balance measurement of glucose and free fatty acid (FFA) uptake (fractional extraction of [9,103H]oleate) and indirect calorimetry across the leg to determine substrate oxidation during fasting and insulin-stimulated conditions. Muscle obtained by percutaneous biopsy had lower carnitine palmitoyl transferase (CPT) activity and oxidative enzyme activity in obesity ( P < 0.05). During fasting conditions, obese subjects had an elevated leg respiratory quotient (RQ, 0.83 ± 0.02 vs. 0.90 ± 0.01; P < 0.01) and reduced fat oxidation but similar FFA uptake across the leg. During insulin infusions, fat oxidation by leg tissues was suppressed in lean but not obese subjects; rates of FFA uptake were similar. Fasting values for leg RQ correlated with insulin sensitivity ( r = −0.57, P < 0.001). Thirty-two of the obese subjects were restudied after weight loss (WL, −14.0 ± 0.9 kg); insulin sensitivity and insulin suppression of fat oxidation improved ( P < 0.01), but fasting leg RQ (0.90 ± 0.02 vs. 0.90 ± 0.02, pre-WL vs. post-WL) and muscle CPT activity did not change. The findings suggest that triglyceride accumulation in skeletal muscle in obesity derives from reduced capacity for fat oxidation and that inflexibility in regulating fat oxidation, more than fatty acid uptake, is related to insulin resistance.
Mice lacking insulin receptor substrate 4 exhibit mild defects in growth, reproduction, and glucose homeostasis
Authors: Fantin Valeria R. , Wang Qing , Lienhard Gustav E. , Keller Susanna R.
Published: December 2017

The insulin receptor substrates (IRSs) function in insulin signaling. Four members of the family, IRS-1 through IRS-4, are known. Previously, mice with targeted disruption of the genes for IRS-1, -2, and -3 have been characterized. To examine the physiological role of IRS-4, we have generated and characterized mice lacking IRS-4. Male IRS-4-null mice were ∼10% smaller in size than wild-type male mice at 9 wk of age and beyond, whereas the female null mice were of normal size. Breeding pairs of IRS-4-null mice reproduced less well than wild-type mice. IRS-4-null mice exhibited slightly lower blood glucose concentration than the wild-type mice in both the fasted and fed states, but the plasma insulin concentrations of the IRS-4-null mice in the fasted and fed states were normal. IRS-4-null mice also showed a slightly impaired response in the oral glucose tolerance test. Thus the absence of IRS-4 caused mild defects in growth, reproduction, and glucose homeostasis.
Enzymatic- and renal-dependent catabolism of the intestinotropic hormone glucagon-like peptide-2 in rats
Authors: Tavares Wendy , Drucker Daniel J. , Brubaker Patricia L.
Published: December 2017

The intestinotropic hormone glucagon-like peptide (GLP)-2-(1—33) is cleaved in vitro to GLP-2-(3—33) by dipeptidyl peptidase IV (DP IV). To determine the importance of DP IV versus renal clearance in the regulation of circulating GLP-2-(1—33) levels in vivo, GLP-2-(1—33) or the DP IV-resistant analog [Gly2]GLP-2 was injected in normal or DP IV-negative rats and assayed by HPLC and RIA. Normal rats showed a steady degradation of GLP-2-(1—33) to GLP-2-(3—33) over time, whereas little or no conversion was detected for GLP-2-(1—33) in DP IV-negative rats and for [Gly2]GLP-2 in normal rats. To determine the role of the kidney in clearance of GLP-2-(1—33) from the circulation, normal rats were bilaterally nephrectomized, and plasma immunoreactive GLP-2 levels were measured. The slope of the disappearance curves for both GLP-2-(1—33) and [Gly2]GLP-2 were significantly reduced in nephrectomized compared with nonnephrectomized rats ( P < 0.01). In contrast to both GLP-2-(1—33) and [Gly2]GLP-2, GLP-2-(3—33) did not stimulate intestinal growth in a murine assay in vivo. Thus the intestinotropic actions of GLP-2-(1—33) are determined both by the actions of DP IV and by the kidney in vivo in the rat.
The reciprocal pool model for the measurement of gluconeogenesis by use of [U-13C]glucose
Authors: Haymond Morey W. , Sunehag Agneta L.
Published: December 2017

To improve upon the [U-13C]glucose method to estimate “gluconeogenesis” as described by J. Katz and J. A. Tayek ( Am. J. Physiol. Endocrinol. Metab. 272: E476–E484, 1997, and 275: E537–E542, 1998), we describe the reciprocal pool model by using only the isotopomer data of plasma glucose during infusion of [U-13C]glucose. The glucose pool serves as both precursor and product for the calculation of the fraction of molecules generated by gluconeogenesis and to correct for exchange and loss of labeled carbon at the level of the tricarboxylic acid cycle. We have applied this model to both our own data and those of other investigators using [U-13C]glucose and have demonstrated excellent agreement between the Katz and Tayek model and our reciprocal pool model. When we compare the results of the reciprocal pool model with those of Hellerstein ([2-13C]glycerol) and Landau (2H2O-glucose-C-5), the results are similar in short- and long-term fasted adult humans. Finally, when we apply the reciprocal pool model to our data from premature infants, it is clear that we account for the inflow of unlabeled glycerol and presumably amino acids. This is not surprising, because the vast majority of gluconeogenesis is the result of recycling of glucose and pyruvate carbon.
Effect of weight reduction, obesity predisposition, and aerobic fitness on skeletal muscle mitochondrial function
Authors: Larson-Meyer D. Enette , Newcomer Bradley R. , Hunter Gary R. , McLean James E. , Hetherington Hoby P. , Weinsier Roland L.
Published: December 2017

We used31P magnetic resonance spectroscopy to measure maximal mitochondrial function in 12 obesity-prone women before and after diet-induced weight reduction and in 12 matched, never-obese, and 7 endurance-trained controls. Mitochondrial function was modeled after maximum-effort plantar flexion from the phosphocreatine recovery time constant (TCPCr), the ADP recovery time constant (TCADP), and the rate of change in PCr during the first 14 s of recovery (OxPhos). Weight reduction was not associated with a significant change in mitochondrial function by TCPCr, TCADP, or OxPhos. Mitochondrial function was not different between postobese and never-obese controls by TCPCr[35.1 ± 2.5 (SE) vs. 34.6 ± 2.5 s], TCADP(22.9 ± 1.8 vs. 21.2 ± 1.8 s), or OxPhos (0.26 ± 0.03 vs. 0.25 ± 0.03 mM ATP/s), postobese vs. never-obese, respectively. However, TCADPwas significantly faster (14.5 ± 2.3 s), and OxPhos was significantly higher (0.38 ± 0.04 mM ATP/s) in the endurance-trained group. These results suggest that maximal mitochondrial function is not impaired in normal-weight obesity-prone women relative to their never-obese counterparts but is increased in endurance-trained women.
Glycogenin activity in human skeletal muscle is proportional to muscle glycogen concentration
Authors: Shearer J. , Marchand I. , Sathasivam P. , Tarnopolsky M. A. , Graham T. E.
Published: December 2017

The de novo biosynthesis of glycogen is catalyzed by glycogenin, a self-glucosylating protein primer. To date, the role of glycogenin in regulating glycogen metabolism and the attainment of maximal glycogen levels in skeletal muscle are unknown. We measured glycogenin activity after enzymatic removal of glucose by α-amylase, an indirect measure of glycogenin amount. Seven male subjects performed an exercise and dietary protocol that resulted in one high-carbohydrate leg (HL) and one low-carbohydrate leg (LL) before testing. Resting muscle biopsies were obtained and analyzed for total glycogen, proglycogen (PG), macroglycogen (MG), and glycogenin activity. Results showed differences ( P < 0.05) between HL and LL for total glycogen (438.0 ± 69.5 vs. 305.7 ± 57.4 mmol glucosyl units/kg dry wt) and PG (311.4 ± 38.1 vs. 227.3 ± 33.1 mmol glucosyl units/kg dry wt). A positive correlation between total muscle glycogen content and glycogenin activity ( r = 0.84, P < 0.001) was observed. Similar positive correlations ( P < 0.05) were also evident between both PG and MG concentration and glycogenin activity (PG, r = 0.82; MG, r = 0.84). It can be concluded that glycogenin does display activity in human skeletal muscle and is proportional to glycogen concentration. Thus it must be considered as a potential regulator of glycogen synthesis in human skeletal muscle.
Mechanisms of increased gluconeogenesis from alanine in rat isolated hepatocytes after endurance training
Authors: Burelle Y. , Fillipi C. , Péronnet F. , Leverve X.
Published: December 2017

This work aimed at further investigating the mechanisms by which liver gluconeogenic capacity from alanine is improved after training in rats, with an isolated hepatocyte model. Compared with controls in hepatocytes from trained rats incubated with gluconeogenic precursors (20 mM), the glucogenic flux ( Jglucose) was increased by 64% from alanine (vs. 21% for glycerol, 18% for lactate-pyruvate 10:1, and 10% for dihydroxyacetone). Maximal intracellular alanine accumulation capacity was also increased by 50%. Further experiments conducted on perifused hepatocytes showed that the putative adaptation at the level of the phospho enolpyruvate-pyruvate cycle, which could be involved in the increased Jglucosefrom lactate-pyruvate, was not involved in the increased Jglucosefrom alanine after training. For alanine concentration higher than ∼1 mM, an increased flux through alanine aminotransferase appeared responsible for the increased Jglucose. This could, in turn, depend on an increased supply of cytosolic 2-oxoglutarate because of the higher mitochondrial respiration observed in hepatocytes from trained rats and the activation of the malate-aspartate shuttle. At lower alanine concentration, the increase in Jglucoseappeared to be entirely due to the improved transport capacity.
Nutritional regulation of binding sites for lipoprotein lipase in rat heart
Authors: Ruge Toralph , Bergö Martin , Hultin Magnus , Olivecrona Gunilla , Olivecrona Thomas
Published: December 2017

Several laboratories have shown that when rats are fasted, the amount of lipoprotein lipase (LPL) at the vascular endothelium in heart (monitored as the amount released by heparin) increases severalfold without corresponding changes in the production of LPL. This suggests that there is a change in endothelial binding of LPL. To study this,125I-labeled bovine LPL was injected. The fraction that bound in the heart was more than twice as high in fasted than in fed rats, 4.3% compared with 1.9% of the injected dose. Refeeding reversed this in 5 h. When unlabeled LPL was injected before the tracer, the fraction of125I-LPL that bound in heart decreased, indicating that the binding was saturable. When isolated hearts were perfused at 4°C with a single pass of labeled LPL, twice as much bound in hearts of fasted rats. We conclude that fasting causes a change in the vascular endothelium in heart such that its ability to bind LPL increases.
The angiotensin II type 2 receptor: an enigma with multiple variations
Authors: Gallinat Stefan , Busche Silke , Raizada Mohan K. , Sumners Colin
Published: December 2017

Since it was discovered ten years ago, the angiotensin II (ANG II) type 2 (AT2) receptor has been an enigma. This receptor binds ANG II with a high affinity but is not responsible for mediating any of the classical physiological actions of this peptide, all of which involve the ANG II type 1 (AT1) receptor. Furthermore, the AT2receptor exhibits dramatic differences in biochemical and functional properties and in patterns of expression compared with the AT1receptor. During the past decade, much information has been gathered about the AT2receptor, and the steadily increasing number of publications indicates a growing interest in this new and independent area of research. A number of studies suggest a role of AT2receptors in brain, renal, and cardiovascular functions and in the processes of apoptosis and tissue regeneration. Despite these advances, nothing stands out as the major singular function of these receptors. The study of AT2receptors has reached a crossroads, and innovative approaches must be considered so that unifying mechanisms as to the function of these unique receptors can be put forward. In this review we will discuss the advances that have been made in understanding the biology of the AT2receptor. Furthermore, we will consider how these discoveries, along with newer experimental approaches, may eventually lead to the elusive physiological and pathophysiological functions of these receptors.
Oxidant damage during and after spaceflight
Authors: Stein T. P. , Leskiw M. J.
Published: December 2017

The objectives of this study were to assess oxidant damage during and after spaceflight and to compare the results against bed rest with 6° head-down tilt. We measured the urinary excretion of the F2isoprostane, 8-iso-prostaglandin (PG) F2α, and 8-oxo-7,8-dihydro-2 deoxyguanosine (8-OH DG) before, during, and after long-duration spaceflight (4–9 mo) on the Russian space station MIR, short-duration spaceflight on the shuttle, and 17 days of bed rest. Sample collections on MIR were obtained between 88 and 186 days in orbit. 8-iso-PGF2αand 8-OH DG are markers for oxidative damage to membrane lipids and DNA, respectively. Data are mean ± SE. On MIR, isoprostane levels were decreased inflight (96.9 ± 11.6 vs. 76.7 ± 14.9 ng ⋅ kg−1⋅ day−1, P < 0.05, n = 6) due to decreased dietary intake secondary to impaired thermoregulation. Isoprostane excretion was increased postflight (245.7 ± 55.8 ng ⋅ kg−1⋅ day−1, P < 0.01). 8-OH DG excretion was unchanged with spaceflight and increased postflight (269 ± 84 vs 442 ± 180 ng ⋅ kg−1⋅ day−1, P < 0.05). On the shuttle, 8-OH DG excretion was unchanged in- and postflight, but 8-iso-PGF2αexcretion was decreased inflight (15.6 ± 4.3 vs 8.0 ± 2.7 ng ⋅ kg−1⋅ day−1, P < 0.05). No changes were found with bed rest, but 8-iso-PGF2αwas increased during the recovery phase (48.9 ± 23.0 vs 65.4 ± 28.3 ng ⋅ kg−1⋅ day−1, P < 0.05). The changes in isoprostane production were attributed to decreased production of oxygen radicals from the electron transport chain due to the reduced energy intake inflight. The postflight increases in the excretion of the products of oxidative damage were attributed to a combination of an increase in metabolic activity and the loss of some host antioxidant defenses inflight. We conclude that 1) oxidative damage was decreased inflight, and 2) oxidative damage was increased postflight.
Hepatic α- and β-adrenergic receptors are not essential for the increase in Raduring exercise in diabetes
Authors: Coker Robert H. , Lacy D. Brooks , Williams Phillip E. , Wasserman David H.
Published: December 2017

The purpose of this study was to determine the role of direct hepatic adrenergic stimulation in the control of endogenous glucose production (Ra) during moderate exercise in poorly controlled alloxan-diabetic dogs. Chronically catheterized and instrumented (flow probes on hepatic artery and portal vein) dogs were made diabetic by administration of alloxan. Each study consisted of a 120-min equilibration, 30-min basal, 150-min moderate exercise, 30-min recovery, and 30-min blockade test period. Either vehicle (control; n = 6) or α (phentolamine)- and β (propranolol)-adrenergic blockers (HAB; n = 6) were infused in the portal vein. In both groups, epinephrine (Epi) and norepinephrine (NE) were infused in the portal vein during the blockade test period to create suprapharmacological levels at the liver. Isotopic ([3-3H]glucose, [U-14C]alanine) and arteriovenous difference methods were used to assess hepatic function. Arterial plasma glucose was similar in controls (345 ± 24 mg/dl) and HAB (336 ± 23 mg/dl) and was unchanged by exercise. Basal arterial insulin was 5 ± 1 mU/ml in controls and 4 ± 1 mU/ml in HAB and fell by ∼50% during exercise in both groups. Basal arterial glucagon was similar in controls (56 ± 10 pg/ml) and HAB (55 ± 7 pg/ml) and rose similarly, by ∼1.4-fold, with exercise in both groups. Despite greater arterial Epi and NE levels in HAB compared with controls during the basal and exercise periods, exercise-induced increases in catecholamines from basal were similar in both groups. Gluconeogenic conversion from alanine and lactate and the intrahepatic efficiency of this process were increased by twofold during exercise in both groups. Rarose similarly by 2.9 ± 0.7 and 2.7 ± 1.0 mg ⋅ kg−1⋅ min−1at time = 150 min during exercise in controls and HAB. During the blockade test period, arterial plasma glucose and Rarose to 454 ± 43 mg/dl and 11.3 mg ⋅ kg−1⋅ min−1in controls, respectively, but were essentially unchanged in HAB. The attenuated response to the blockade test in HAB substantiates the effectiveness of the hepatic adrenergic blockade. In conclusion, these results demonstrate that direct hepatic adrenergic stimulation does not play a role in the stimulation of Raduring exercise in poorly controlled diabetes.
Hyperglycemia contributes insulin resistance in hepatic and adipose tissue but not skeletal muscle of ZDF rats
Authors: Nawano Masao , Oku Akira , Ueta Kiichiro , Umebayashi Itsuro , Ishirahara Tomomi , Arakawa Kenji , Saito Akira , Anai Motonobu , Kikuchi Masatoshi , Asano Tomoichiro
Published: December 2017

To determine the contribution of hyperglycemia to the insulin resistance in various insulin-sensitive tissues of Zucker diabetic fatty (ZDF) rats, T-1095, an oral sodium-dependent glucose transporter (SGLT) inhibitor, was administered by being mixed into food. Long-term treatment with T-1095 lowered both fed and fasting blood glucose levels to near normal ranges. A hyperinsulinemic euglycemic clamp study that was performed after 4 wk of T-1095 treatment demonstrated partial recovery of the reduced glucose infusion rate (GIR) in the T-1095-treated group. In the livers of T-1095-treated ZDF rats, hepatic glucose production rate (HGP) and glucose utilization rate (GUR) showed marked recovery, with almost complete normalization of reduced glucokinase/glucose-6-phosphatase (G-6-Pase) activities ratio. In adipose tissues, decreased GUR was also shown to be significantly improved with a normalization of insulin-induced GLUT-4 translocation. In contrast, in skeletal muscles, the reduced GUR was not significantly improved in response to amelioration of hyperglycemia by T-1095 treatment. These results suggest that the contribution of hyperglycemia to insulin resistance in ZDF rats is very high in the liver and considerably elevated in adipose tissues, although it is very low in skeletal muscle.
Meal-induced insulin secretion in dogs is mediated by both branches of the autonomic nervous system
Authors: Benthem Lambertus , Mundinger Thomas O. , Taborsky Gerald J.
Published: December 2017

We investigated the relationship between autonomic activity to the pancreas and insulin secretion in chronically catheterized dogs when food was shown, during eating, and during the early absorptive period. Pancreatic polypeptide (PP) output, pancreatic norepinephrine spillover (PNESO), and arterial epinephrine (Epi) were measured as indexes for parasympathetic and sympathetic nervous activity to the pancreas and for adrenal medullary activity, respectively. The relation between autonomic activity and insulin secretion was confirmed by autonomic blockade. Showing food to dogs initiated a transient increase in insulin secretion without changing PP output or PNESO. Epi did increase, suggesting β2-adrenergic mediation, which was confirmed by β-adrenoceptor blockade. Eating initiated a second transient insulin response, which was only totally abolished by combined muscarinic and β-adrenoceptor blockade. During absorption, insulin increased to a plateau. PP output showed the same pattern, suggesting parasympathetic mediation. PNESO decreased by 50%, suggesting withdrawal of inhibitory sympathetic neural tone. We conclude that 1) the insulin response to showing food is mediated by the β2-adrenergic effect of Epi, 2) the insulin response to eating is mediated both by parasympathetic muscarinic stimulation and by the β2-adrenergic effect of Epi, and 3) the insulin response during early absorption is mediated by parasympathetic activation, with possible contribution of withdrawal of sympathetic neural tone.
Metabolic regulation of Na+/Pi-cotransporter-1 gene expression in H4IIE cells
Authors: Xie Zijian , Li Hui , Liu Liqin , Kahn Barbara B. , Najjar Sonia M. , Shah Waqar
Published: December 2017

We showed that the rat Na+/Picotransporter-1 (RNaPi-1) gene was regulated by insulin and glucose in rat hepatocytes. The aim of this work was to elucidate signaling pathways of insulin-mediated metabolic regulation of the RNaPi-1 gene in H4IIE cells. Insulin increased RNaPi-1 mRNA abundance in the presence of glucose and decreased RNaPi-1 mRNA in the absence of glucose, clearly establishing an involvement of metabolic signals for insulin-induced upregulation of the RNaPi-1 gene. Pyruvate and insulin increased RNaPi-1 expression but downregulated L-pyruvate kinase, indicating the existence of gene-specific metabolic signals. Although fructose, glycerol, and lactate could support insulin-induced upregulation of the RNaPi-1 gene, compounds entering metabolism beyond pyruvate oxidation, such as acetate and citrate, could not, suggesting that RNaPi-1-specific metabolic signals are generated at or above pyruvate oxidation. Wortmannin, LY-294002, and rapamycin abolished the insulin effect on the RNaPi-1 gene, whereas expression of dominant negative Asn17Ras and mitogen-activating protein kinase (MAPK) kinase (MEK) inhibitor PD-98059 exhibited no effect. Thus we herein propose that metabolic regulation of RNaPi-1 expression by insulin is mediated through the phosphatidylinositol 3-kinase/p70 ribosomal S6 kinase pathways, but not the Ras/MAPK pathway.