bluuebunny/crossref_metadata_2025 huggingface dataset:
A model of skeletal muscle leucine kinetics measured across the human forearm
Authors: Tessari P. , Inchiostro S. , Zanetti M. , Barazzoni R.
Published: December 2017

We propose a new six-compartment model of intracellular muscle kinetics of leucine and of its transamination product alpha-ketoisocaproic acid (KIC) by combining systemic tracer infusions of [14C]- and [15N]leucine with the arterial-deep venous catheterization of the human forearm. Venous [14C]KIC specific activity (SA) is taken as representative of intracellular [14C]leucine SA, whereas net [15N]leucine disposal is used to calculate leucine inflow and outflow across forearm cell membrane(s). In post-absorptive normal subjects, model-derived rates of intracellular leucine release from and incorporation into protein were approximately 32% (P = 0.03) and approximately 37% greater (P = 0.025), respectively, than those calculated using a conventional arteriovenous approach. Forearm fasting proteolysis exceeded protein synthesis (P < 0.025), whereas leucine oxidation was greater than zero (P < 0.01), suggesting a net negative leucine (i.e., protein) balance. Leucine inflow from blood to cell represented approximately 30% of arterial leucine delivery; therefore approximately 70% of arterial leucine bypassed intracellular metabolism. This model provides a comprehensive description of regional leucine and KIC kinetics and new estimates of protein degradation and synthesis across the human forearm.
Arginine enhances glycogen synthesis in response to insulin in 3T3-L1 adipocytes
Authors: Egan J. M. , Henderson T. E. , Bernier M.
Published: December 2017

The present study was undertaken to define the role of L-arginine (L-Arg) in glucose metabolism in differentiated 3T3-L1 adipocytes in culture. L-Arg alone had no effect on 2-deoxyglucose uptake or basal glycogen synthesis, but this amino acid increased by 153 +/- 10% (P < 0.01) the incorporation of glucose into glycogen in insulin-treated cells. L-Glutamate (L-Glu), a major metabolite of L-Arg, also enhanced insulin-stimulated glycogen synthesis. The response to insulin was not altered by L-lysine (L-Lys), but the effect of L-Arg was markedly attenuated by L-Lys. Cell incubation with L-Arg markedly enhanced arginase-mediated urea synthesis, whereas L-Lys abolished this response. The stimulatory effect of L-Arg on insulin-stimulated glycogen synthesis did not appear to be accounted for by the generation of polyamines or the production of nitric oxide, both potentially derived from the enzymatic conversion of L-Arg. In the presence of insulin, cellular ATP levels were significantly increased by L-Arg, L-Glu, and L-Lys as well. These data suggest that metabolic degradation of L-Arg not related to citric acid cycle activity is important in the mechanism by which L-Arg enhances insulin-stimulated glycogen synthesis.
Vitamin E prevents diabetes-induced abnormal retinal blood flow via the diacylglycerol-protein kinase C pathway
Authors: Kunisaki M. , Bursell S. E. , Clermont A. C. , Ishii H. , Ballas L. M. , Jirousek M. R. , Umeda F. , Nawata H. , King G. L.
Published: December 2017

We have characterized effects of d-alpha-tocopherol (vitamin E) on activation of protein kinase C (PKC) and diacylglycerol (DAG) levels in retinal tissues of diabetic rats and correlated its effects to diabetes-induced changes in retinal hemodynamics. Membrane PKC specific activities were increased by 71% in streptozocin-induced diabetic rats compared with controls (P < 0.05). Western blot analysis showed that membrane PKC-beta II was increased by 133 +/- 5% (P < 0.05). Injection of d-alpha-tocopherol (40 mg/kg ip) every other day prevented the increases in membrane PKC specific activity and PKC-beta II protein by immunoblots. Diabetes-induced increases in DAG levels were also normalized by d-alpha-tocopherol treatment of 2 wk duration. Physiologically, angiographic abnormalities of retinal hemodynamics based on computerized video-based fluorescein angiography and associated with increases of DAG and membranous PKC levels were also prevented by d-alpha-tocopherol treatment in diabetic rats. The effect of d-alpha-tocopherol on retinal vascular cells was also studied. Exposure of retinal endothelial cells to 22 mM glucose for 3 days increased total DAG and [3H]palmitate-labeled DAG levels by 35 +/- 8 and 50 +/- 8% (P < 0.05), respectively, compared with exposure to 5.5 mM glucose. The presence of d-alpha-tocopherol (50 micrograms/ml) prevented the increases in total DAG and [3H]palmitate-labeled DAG levels in cells exposed to 22 mM glucose. These findings suggested that treatment with d-alpha-tocopherol can prevent diabetes-induced abnormalities in rat retinal blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)
Pentagastrin increases pepsin secretion without increasing its fractional synthetic rate
Authors: Corbett M. E. , Boyd E. J. , Penston J. G. , Wormsley K. G. , Watt P. W. , Rennie M. J.
Published: December 2017

We studied the effects of increasing doses of pentagastrin on gastric secretion of pepsin and on incorporation of L-[1-13C]leucine into gastric aspirate protein as an index of pepsin synthesis. Pentagastrin (0.25-4.0 micrograms.kg-1.h-1) significantly increased pepsin output from basal 76 mg/h to < or = 181 mg/h but did not significantly alter incorporation of L-[1-13C]leucine from the basal fractional synthetic rate of 3.63 +/- 0.05%/h. In four subjects in whom infusion of tracer leucine was continued for > 1 day, aspiration of pepsin between 24 and 27 h demonstrated that plateau 13C labeling of leucine in pepsin had been attained, but at a value that was only 48% of the 13C labeling of plasma alpha-ketoisocaproic acid (alpha-KIC) [0.730 +/- 0.02 (SE) vs. 1.520 +/- 0.14 atoms %excess]. This suggests that actual rates of pepsin synthesis were approximately double those calculated on the basis of alpha-KIC labeling. The results are consistent with an interpretation that increasing doses of pentagastrin cause increased secretion of pepsinogen by recruitment of gastric chief cells, each synthesizing pepsinogen at an unaltered rate. Plateau 13C enrichment of alpha-KIC may not be a valid surrogate for plateau 13C leucine enrichment when fractional synthetic rates of some secreted proteins are calculated.
Mechanotransduction in bone: role of strain rate
Authors: Turner C. H. , Owan I. , Takano Y.
Published: December 2017

Bone tissue can detect and respond to its mechanical environment, but there is no consensus for how bone cells detect mechanical loads. Some think that cells sense tissue deformation (strain) and respond when strain is abnormally high. However, strains in bone tissue are usually very small, and it is questionable whether bone cells are sensitive enough to detect them. Another theory suggests that mechanical loads are coupled to the bone cells by stress-generated fluid flow within the bone tissue, which is dependent on the rate of change of bone strain. We applied bending loads to the tibiae of adult rats to create equivalent peak strains in the bone tissue but with varied rates of strain. Bone formation was significantly increased in the two experimental groups when the highest strain rates were compared with lower strain rates (P < 0.01), and the amount of new bone formation was directly proportional to the rate of strain in the bone tissue. These results suggest that relatively large strains alone are not sufficient to activate bone cells. High strain rates and possibly stress-generated fluid flow are required to stimulate new bone formation.
Glutamate stimulates insulin secretion and improves glucose tolerance in rats
Authors: Bertrand G. , Puech R. , Loubatieres-Mariani M. M. , Bockaert J.
Published: December 2017

We previously showed in vitro that glutamate stimulates insulin release via an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor. Here we address a more physiological question concerning the in vivo effect of intravenously or orally administered glutamate on insulinemia and glycemia in fed and fasted rats. In anesthetized fed rats, the intravenous administration of glutamate at 9 and 30 mg/kg transiently increased insulinemia in a dose-dependent manner. The insulin-secretory effect of glutamate (9 mg/kg) was blocked by an antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. In anesthetized fasted rats, glutamate at 9 mg/kg was ineffective, but during an intravenous glucose tolerance test (0.5 g/kg), glutamate markedly potentiated insulin release and increased the glucose disappearance rate. In conscious rats, the intragastric administration of glutamate at 200 mg/kg elicited a transient insulin response in fed animals and had no effect in fasted animals but, during an oral glucose tolerance test (1 g/kg), enhanced insulin secretion and reduced the hyperglycemia. Glutamate was effective at plasma concentrations of 200-300 microM. In conclusion, intravenously and orally administered glutamate stimulates insulin secretion in vivo via an excitatory amino acid receptor and improves glucose tolerance.
Determinants of cardiac fibrosis in experimental hypermineralocorticoid states
Authors: Young M. , Head G. , Funder J.
Published: December 2017

Uninephrectomized rats maintained on 1.0% NaCl to drink and infused with aldosterone (0.75 microgram/h) for 8 wk have previously been shown to develop hypertension, cardiac hypertrophy, and cardiac fibrosis. In the present study we have shown that K+ supplementation (1.0% NaCl plus 0.4% KCl drinking solution) alters neither the interstitial nor the perivascular fibrotic response to mineralocorticoid treatment. Second, rats receiving 0.75 microgram/h 9 alpha-fluorocortisol, a mineralocorticoid and glucocorticoid agonist, respond with hypertension and cardiac fibrosis without cardiac hypertrophy. Finally, intracerebroventricular infusion of the mineralocorticoid receptor antagonist RU-28318 blocks blood pressure elevation, but not cardiac hypertrophy or fibrosis, when aldosterone is coinfused peripherally. We conclude that the myocardial fibrosis observed in response to chronic mineralocorticoid elevation and salt loading is a humorally mediated event independent of hypokalemia, hypertension, and cardiac hypertrophy. It remains to be determined whether the fibrosis observed in the presence of excess salt represents a direct (e.g., cardiac) effect of mineralocorticoid hormones or one mediated via a primary action on classical epithelial aldosterone target tissues (e.g., kidney).
Lactate transport studied in sarcolemmal giant vesicles from rat skeletal muscles: effect of denervation
Authors: Pilegaard H. , Juel C.
Published: December 2017

The effect of denervation on lactate transport capacity was studied in giant sarcolemmal vesicles obtained from rat muscle. The rate of lactate transport was determined in soleus and red (RG) and white gastrocnemius (WG) after 1, 3, and 21 days of denervation and in the corresponding contralateral muscles. In addition, muscle lactate dehydrogenase (LDH) and succinate dehydrogenase (SDH) activities were determined. After 1, 3, and 21 days of denervation the rate of lactate transport was lower (P < 0.05) in WG (9, 11, and 36%), RG (15, 21, and 41%), and soleus (12, 24, and 50%) compared with the contralateral muscles. After 21 days of denervation LDH activity was 26, 25, and 34% and SDH activity 33, 25, and 27% lower (P < 0.05) in WG, RG, and soleus, respectively, compared with the contralateral muscles. In the control muscles the lactate transport capacity was 20 and 32% lower (P < 0.05) in WG than in RG and soleus, respectively. The present findings provide support that the sarcolemmal lactate carrier is a plastic system; the transport capacity in soleus, RG, and WG already declines after 1 day of denervation and is further reduced after 21 days of denervation. In addition, the data suggest that the lactate transport capacity in fast-twitch glycolytic fibers < fast-twitch oxidative-glycolytic fibers < slow-twitch oxidative fibers.
Compensatory alterations for insulin signal transduction and glucose transport in insulin-resistant diabetes
Authors: Bonini J. A. , Colca J. R. , Dailey C. , White M. , Hofmann C.
Published: December 2017

Insulin binding activates the receptor tyrosine kinase toward the insulin receptor substrate-1 (IRS-1). Phosphorylated IRS-1 then interacts with the p85 alpha subunit of phosphatidylinositol 3-kinase (PI3K), Nck, growth factor receptor-bound protein 2 (GRB2), and Syp, thus branching insulin's signal for both mitogenic and metabolic responses. To determine whether the expression of these proteins is altered in insulin resistance, the levels of these proteins were compared in adipose and liver tissues of nondiabetic mice and obese insulin-resistant diabetic KKAy mice. IR and PI3K p85 alpha protein levels were significantly lower in KKAy mice than in control nondiabetic mice, whereas IRS-1 protein levels were not altered. In contrast, the protein levels of GRB2, Nck, Syp, and GLUT-1 were dramatically elevated in KKAy fat, with less striking changes in liver. Treatment of diabetic animals with pioglitazone, an insulin-sensitizing antihyperglycemic agent, partially corrected the expression of some of these proteins. Taken together, these findings suggest that the insulin-resistant diabetic condition is characterized by changes in expression of insulin signal transduction components that may be associated with altered glucose metabolism.
Quantitation of hepatic glucose fluxes and pathways of hepatic glycogen synthesis in conscious mice
Authors: Massillon D. , Chen W. , Hawkins M. , Liu R. , Barzilai N. , Rossetti L.
Published: December 2017

Mice were studied with the euglycemic hyperinsulinemic and the hyperglycemic clamp techniques after a 6-h fast: 1) euglycemic (6.7 +/- 0.2 mM) hyperinsulinemia (approximately 800 microU/ml); 2) hyperglycemic (15.3 +/- 0.4 mM) hyperinsulinemia (approximately 800 microU/ml). All mice received an infusion of [3-3H]glucose and [U-14C]lactate. Basal hepatic glucose production (HGP) averaged approximately 170 mumol.kg-1.min-1 in both groups. During euglycemic and hyperglycemic hyperinsulinemia, HGP decreased by 53% (to 76.7 +/- 11.1 mumol.kg-1.min-1; P < 0.01) and 74% (to 43.3 +/- 7.2 mumol.kg-1.min-1; P < 0.01), respectively. Hyperglycemia increased glucose cycling (by 2.1-fold; P < 0.01) and the contribution of gluconeogenesis to HGP (88 vs. 43%; P < 0.01) while decreasing that of glycogenolysis (12 vs. 57%; P < 0.01). The percentage of neosynthetized hepatic glycogen formed via the direct pathway was markedly increased during hyperglycemia (53 +/- 2% vs. 23 +/- 3%; P < 0.01): These data indicate that the assessment of hepatic glucose fluxes can be accomplished in conscious unrestrained mice and that, in the presence of hyperinsulinemia, hyperglycemia causes 1) a further inhibition of HGP mainly via inhibition of glycogenolysis and increase in hepatic glucose cycling; and 2) about a fivefold stimulation in the direct pathway of hepatic glycogen formation.
Involvement of alpha 2-adrenoceptors in metabolic and hormonal responses to a mixed meal in beagle dogs
Authors: Guillot E. , Morand R. , Bouloy C. , Eon M. T. , Angel I.
Published: December 2017

The effects of alpha 2-adrenoceptor blockade or activation on glucose, insulin, free fatty acids (FFA), and glycerol responses to a mixed meal were studied in the beagle dog. The alpha 2-adrenoceptor antagonist deriglidole (1 mg/kg po), administered 45 min before feeding, significantly reduced glycemia and increased insulin, FFA, and glycerol levels. Although the alpha 2-adrenoceptor agonist UK-14.304 (3 micrograms/kg sc), administered 15 min before feeding, had no effect per se, it completely blocked meal-induced insulin release, thus promoting a mild increase in glycemia, and prolonged the meal-induced FFA decrease. Deriglidole antagonized the reduction of insulin secretion and the hyperglycemia induced by UK-14.304. The meal-induced fall in FFA levels was still observed after deriglidole treatment and was markedly amplified when UK-14.304 was administered with deriglidole. These results suggest that, in the dog, insulin release and lipolysis are very sensitive to alpha 2-adrenoceptor stimulation. It is also suggested that the meal-evoked decrease in lipid mobilization results from an increase in alpha 2-adrenoceptor stimulation rather than from an increase in insulin secretion.
Comparison of 22-oxacalcitriol and 1,25(OH)2D3 on bone metabolism in young X-linked hypophosphatemic male mice
Authors: Halstead L. R. , Weinstein R. S. , Cheng S. L. , Rifas L. , Avioli L. V.
Published: December 2017

Using a mouse model (Hyp) of human hypophosphatemic vitamin D-resistant rickets [X-linked hypophosphatemia (XLH)], we compared the effects of 22-oxa-1,25-dihydroxyvitamin D3 (OCT) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on restoring defects in mineral and skeletal metabolism. Hyp/Y mice received OCT or 1,25(OH)2D3 at doses of 0.05-0.25 micron.kg-1.day-1 for 4 wk. OCT normalized serum calcium levels, whereas 1,25(OH)2D3 produced hypercalcemia in Hyp/Y. OCT and 1,25(OH)2D3 also normalized serum phosphate levels and increased urinary calcium levels. Additionally, OCT and 1,25(OH)2D3 reduced elevated urinary pyridinoline levels and suppressed urinary adenosine 3',5'-cyclic monophosphate levels to normal. Bone ash content was low in Hyp/Y, and OCT was more effective than 1,25(OH)2D3 in reversing this defect. Histomorphometric analysis of bone turnover, mineralization rate, and osteoid content demonstrated comparable responses with OCT and 1,25(OH)2D3, although the highest dose of 1,25(OH)2D3 resulted in increased osteoid content and delayed mineralization. OCT appears to be more effective and definitely less toxic than 1,25(OH)2D3 in reversing skeletal lesions in Hyp/Y mice and may prove to be the drug of choice in the treatment of childhood XLH.
Effects of dietary protein restriction on regional amino acid metabolism in insulin-dependent diabetes mellitus
Authors: Brodsky I. G. , Devlin J. T.
Published: December 2017

We studied subjects with insulin-dependent diabetes mellitus (IDDM) and controls by administering primed continuous infusions of L-[1-13C,15N)]leucine and L-[2,3-13C2]alanine to measure whole body and forearm metabolism of these amino acids during ample protein intake and again after 4 wk of moderately restricted protein intake. Decreased rates of whole body protein degradation, leucine transamination, leucine oxidation, and increased forearm alanine release produced by dietary protein restriction occurred equivalently in IDDM subjects under short-term tightly managed glycemia and in controls. Dietary protein restriction did not affect whole body alanine appearance or forearm leucine appearance, disposal, or balance in IDDM subjects or controls. IDDM subjects differed from controls only in that normal forearm leucine balance was maintained at higher rates of leucine appearance and disposal. We conclude that IDDM subjects adapt normally to dietary protein restriction. Undernutrition during moderate protein deprivation in these patients likely occurs during episodes of poor glycemic control.
Exercise-induced increase in glucose transport, GLUT-4, and VAMP-2 in plasma membrane from human muscle
Authors: Kristiansen S. , Hargreaves M. , Richter E. A.
Published: December 2017

A major effect of muscle contractions is an increase in sarcolemmal glucose transport. We have used a recently developed technique to produce sarcolemmal giant vesicles from human muscle biopsy samples obtained before and after exercise. Six men exercised for 10 min at 50% maximal O2 uptake (Vo2max) and then to fatigue at 100% Vo2max (5.7 +/- 0.2 min). Vesicle glucose transport at 5 mM increased from 3.3 +/- 0.6 pmol.microgram-1.min-1 at rest to 6.6 +/- 1.0 pmol.microgram-1.min-1 at fatigue (mean +/- SE, n = 6, P < 0.05). This increase in glucose transport was associated with a 1.6-fold increase in vesicle GLUT-4 protein content. Glucose transport normalized to GLUT-4 protein content also increased with exercise, suggesting increased intrinsic activity of GLUT-4. Furthermore, exercise resulted in a 1.4-fold increase in sarcolemmal vesicle-associated membrane protein (VAMP-2) content, suggesting that muscle contractions may induce trafficking of GLUT-4-containing vesicles via a mechanism similar to neurotransmitter release. Our results demonstrate for the first time exercise-induced translocation of GLUT-4 and VAMP-2 to the plasma membrane of human muscle and increased sarcolemmal glucose transport.
Pancreatic sympathetic nerves contribute to increased glucagon secretion during severe hypoglycemia in dogs
Authors: Havel P. J. , Mundinger T. O. , Taborsky G. J.
Published: December 2017

To determine if pancreatic sympathetic nerves can contribute to increased glucagon secretion during hypoglycemia, plasma glucagon and pancreatic glucagon secretion in situ were measured before and during insulin-induced hypoglycemia in three groups of halothane-anesthetized dogs. All dogs were bilaterally vagotomized to eliminate the input from pancreatic parasympathetic nerves. One group of dogs received only vagotomy (VAGX). A second group was vagotomized and adrenalectomized (VAGX + ADX). A third group received vagotomy, adrenalectomy, plus surgical denervation of the pancreas (VAGX + ADX + NERVX) to prevent activation of pancreatic sympathetic nerves. In dogs with VAGX only, hypoglycemia increased plasma epinephrine (Epi), pancreatic norepinephrine (NE) output (+320 +/- 140 pg/min, P < 0.05), arterial plasma glucagon (+28 +/- 12 pg/ml, P < 0.01), and pancreatic glucagon output (+1,470 +/- 370 pg/min, P < 0.01). The addition of ADX eliminated the increase of Epi but did not increase pancreatic NE output (+370 +/- 190 pg/min, P < 0.025), arterial plasma glucagon (+20 +/- 5 pg/ml, P < 0.01), or pancreatic glucagon output (+810 +/- 200 pg/min, P < 0.01). In contrast, the addition of pancreatic denervation eliminated the increase of pancreatic NE output (-20 +/- 40 pg/min, P < 0.05 vs. VAGX), the arterial glucagon (+1 +/- 2 pg/ml, P < 0.01 vs. VAGX), and pancreatic glucagon output responses (+210 +/- 280 pg/min, P < 0.025 vs. VAGX) to hypoglycemia. Thus activation of pancreatic sympathetic nerves can contribute to the increased glucagon secretion during severe insulin-induced hypoglycemia in dogs.
Cortical bone growth and maturational changes in dwarf rats induced by recombinant human growth hormone
Authors: Martinez D. A. , Orth M. W. , Carr K. E. , Vanderby R. , Vailas A. C.
Published: December 2017

The growth hormone (GH)-deficient dwarf rat was used to investigate recombinant human (rh) GH-induced bone formation and to determine whether rhGH facilitates simultaneous increases in bone formation and bone maturation during rapid growth. Twenty dwarf rats, 37 days of age, were randomly assigned to dwarf plus rhGH (GH; n = 10) and dwarf plus vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt two times daily for 14 days. Biochemical, morphological, and X-ray diffraction measurements were performed on the femur middiaphysis. rhGH stimulated new bone growth in the GH group, as demonstrated by significant increases (P < 0.05) in longitudinal bone length (6%), middiaphyseal cross-sectional area (20%), and the amount of newly accreted bone collagen (28%) in the total pool of middiaphyseal bone collagen. Cortical bone density, mean hydroxyapatite crystal size, and the calcium and collagen contents (microgram/mm3) were significantly smaller in the GH group (P < 0.05). Our findings suggest that the processes regulating new collagen accretion, bone collagen maturation, and mean hydroxyapatite crystal size may be independently regulated during rapid growth.
Interleukin-1 receptor antagonist inhibits endotoxin fever and systemic interleukin-6 induction in the rat
Authors: Luheshi G. , Miller A. J. , Brouwer S. , Dascombe M. J. , Rothwell N. J. , Hopkins S. J.
Published: December 2017

Although a number of studies indicate that the pyrogenic activity of lipopolysaccharide (LPS) and/or interleukin (IL)-1 is mediated via induction of IL-6, this has been questioned by recent evidence demonstrating a dissociation between fever and circulating IL-6. The present study reexamines this relationship by use of human recombinant interleukin-1 receptor antagonist (IL-1ra). Injection of LPS (100 micrograms/kg ip) into rats induced fever (2.0 degrees C) that was significantly inhibited (P < 0.05) when IL-1ra (16 mg/kg ip) was given 1 and 2 h after LPS. The rise in plasma IL-6 preceded the febrile response by 1-1.5 h and, although the concentrations of bioactive IL-6 in plasma and cerebrospinal fluid (CSF) were not reduced at 4 h, at 2 h plasma and CSF IL-6 bioactivity was inhibited by 80 and 70%, respectively, after a single injection of IL-1ra (16 mg/kg ip). Intracerebroventricular injection of IL-1ra (200 micrograms/rat) inhibited LPS fever but did not affect the plasma IL-6 bioactivity measured 2 or 4 h after intraperitoneal LPS. These data show that peripheral IL-1 plays a part in the induction of both fever and the rise in plasma IL-6 that precedes it, and that IL-1 within the brain is also important in the induction of fever by LPS.
Multiple forms of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase are expressed in perinatal rat liver
Authors: Casado M. , Bosca L. , Martin-Sanz P.
Published: December 2017

Fetal rat liver expresses a 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/Fru-2,6-Pase2) form that differs from the adult liver enzyme in the inhibition by phosphorylation by the adenosine 3',5'-cyclic monophosphate-dependent protein kinase and in the recognition by an antibody specific for the NH2-terminal domain of the adult liver enzyme. Northern blot analysis shows that fetal hepatocytes contain a species of mRNA that is 2.2 kb in size and that exhibits the maximal levels after delivery. PFK-2/Fru-2,6-Pase2 mRNA analysis using a sensitive ribonuclease protection assay reveals the presence of nearly similar amounts of adult liver-specific and skeletal muscle-specific mRNA in fetal liver and hepatocytes during the last days of gestation, as well as a 233-bp protected fragment present in fetal liver. These results were confirmed by polymerase chain reaction using specific oligonucleotide pairs. Primer extension of fetal liver cDNA suggests the presence of two initiation sites of transcription. Analysis of the adult liver PFK-2/Fru-2,6-Pase2 protein during the perinatal transition using a specific antibody shows a marked accumulation of this form immediately after birth.
Consequences of high dietary fructose in the islet-transplanted rat with suboptimal beta-cell mass
Authors: Bell R. C. , Ryan E. A. , Finegood D. T.
Published: December 2017

Fructose (FR) feeding in rats provides a model of dietary-induced insulin resistance that has been used to examine interactions among the cluster of metabolic disorders including insulin resistance, hyperinsulinemia, hypertension, and dyslipidemia known as Syndrome X. In animals with reduced beta-cell mass, however, insulin resistance may not have similar associated disorders. Therefore this study examined the consequences of FR feeding in rats with a reduced beta-cell mass. Formerly diabetic islet-transplanted (TX) or shamoperated (SHAM) male Wistar Furth rats were fed a purified control (CNTL) diet or a diet containing either 40 or 70% (wt/wt) FR for 3-5 wk. FR feeding in SHAM animals resulted in elevated triglyceride levels but did not affect fed or fasting glucose and insulin concentrations, blood pressure, glucose tolerance, and the acute insulin response to a glucose bolus compared with CNTL-fed animals. Among TX animals, hypertriglyceridemia and fasting hyperglycemia were observed only in those fed FR. Thus the effects of diet-induced insulin resistance are limited to dyslipidemia, if insulin secretory capacity is adequate, but are detrimental to both glucose and lipid metabolism in combination with a reduced beta-cell mass.
Metabolic changes in rats during a continuous infusion of recombinant interleukin-1
Authors: Ling P. R. , Schwartz J. H. , Jeevanandam M. , Gauldie J. , Bistrian B. R.
Published: December 2017

The effects of recombinant interleukin-1 (IL-1), given as a continuous infusion for 6 days, on host responses were determined in rats. The development of fever, change in food intake and body weight, and key components of the acute-phase response in energy and protein metabolism were assessed. The effects of IL-1 were compared with those observed in a matched pair-fed group (semistarved), to distinguish the contribution from anorexia, and in a group that received IL-1 for 4 h acutely. IL-1 significantly increased core temperature, plasma levels of IL-6, and acute-phase protein production and decreased food intake and the circulating zinc level. The catabolic effects of IL-1 on nitrogen loss and muscle protein breakdown were independent of, and additive to those from malnutrition. The changes in energy expenditure, cumulative urinary nitrogen, and hydroxyproline excretion in the chronic IL-1 group were increased over semistarved animals. Finally, changes in muscle protein kinetics were only seen with chronic IL-1 infusion, and the changes in acute-phase protein were greater.
Gender differences in muscle sympathetic nerve activity: effect of body fat distribution
Authors: Jones P. P. , Snitker S. , Skinner J. S. , Ravussin E.
Published: December 2017

Muscle sympathetic nerve activity (MSNA) has been correlated with percent body fat (%BF) in males. Because MSNA is typically lower and %BF higher in females, we tested whether this relationship could be generalized to females. Because abdominal-visceral body fat in men may be responsible for elevated sympathetic activity, we hypothesized that an estimate [waist-to-thigh ratio (W/T)] would correlate positively with MSNA in both genders and account for higher MSNA in males. Microneurography, hydrodensitometry, and W/T measures were obtained in 14 males and 14 females with a large range of %BF and W/T. Regression analyses revealed positive correlations between MSNA and %BF in males (r = 0.55, P = 0.04) and in females (r = 0.63, P = 0.02), with no difference in the slopes of the regression lines but a higher intercept in males (P < 0.01). When genders were pooled, MSNA and W/T were correlated (r = 0.68, P < 0.0001); this positive correlation was also found in males (r = 0.57, P = 0.04) but not as strongly in females (r = 0.49, P = 0.07). Forward stepwise multiple-regression analysis using %BF, W/T, gender, and age indicated that W/T was the primary factor related to MSNA (R2 = 0.46); the other factors were not independent predictors. It is concluded that %BF is related to MSNA in both males and females but that the regression line is shifted downward in females because of lower levels of MSNA. W/T is a better correlate of MSNA than %BF and partially explains the higher MSNA in males. These findings may be relevant to the cardiovascular and metabolic disease risk associated with abdominal obesity.
Effect of aging on the metabolism of phosphorus and 1,25-dihydroxyvitamin D in healthy men
Authors: Portale A. A. , Halloran B. P. , Morris R. C. , Lonergan E. T.
Published: December 2017

We tested the hypothesis that aging alters physiological regulation of the serum concentration of 1,25-dihydroxyvitamin D [1,25(OH)2D] by inorganic phosphorus. In seven elderly men [age 71 +/- 1 (SE) yr] and 9 young men (29 +/- 2 yr), dietary phosphorus was first normal, then increased and decreased within its normal range. At each intake of phosphorus, serum concentrations of 1,25(OH)2D in the elderly did not differ from those in young men, but fasting and 24-h mean serum concentrations of phosphorus were lower in elderly men. With phosphorus restriction, in each group serum 1,25(OH)2D increased by 47%, and 24-h mean serum phosphorus decreased by 0.6 +/- 0.1 mg/dl. Serum concentrations of 1,25(OH)2D varied inversely with 24-h mean serum phosphorus (R= -0.92, P<0.0001). Thus, in healthy elderly men in whom glomerular filtration rate is normal or near normal, serum concentrations of 1,25(OH)2D increase when dietary phosphorus is restricted; the magnitude of response at steady state is unaffected by aging, but the time course of response is delayed. At any level of serum phosphorus, serum 1,25(OH)2D is lower than that in young men, as reflected by a lower intercept of regression of serum 1,25(OH)2D on 24-h mean phosphorus.
Altered regulation of hepatic glucose output in the male offspring of protein-malnourished rat dams
Authors: Ozanne S. E. , Smith G. D. , Tikerpae J. , Hales C. N.
Published: December 2017

Offspring of protein-malnourished rat dams have permanent alterations in hepatic enzyme activities associated with glucose homeostasis. Hormonal control of hepatic glucose output (HGO) was studied in male offspring of dams fed either a 20% (control) or 8% (low protein) protein diet during pregnancy and lactation. Glucagon (210 pM) stimulated HGO significantly more (P < 0.04) in controls (from 0.72 +/- 0.11 to 3.18 +/- 0.30 mumol.min-1.g liver-1) compared with low-protein animals (from 0.53 +/- 0.11 to 2.05 +/- 0.24 mumol.min-1.g liver-1). Insulin (1 nM) decreased (P < 0.001) HGO in controls to 2.39 +/- 0.37 mumol.min-1.g liver-1 after 10 min but increased HGO (to 2.82 +/- 0.40 mumol.min-1.g liver-1; P < 0.04) in low-protein rats. There were fivefold fewer (P = 0.01) glucagon receptors but a threefold increase (P < 0.05) in hepatic insulin receptor number in the low-protein rats, which was reflected by increased in insulin degradation (P < 0.001). The glucose transporter GLUT-2 was also raised threefold in the low-protein group (P < 0.001). The anomalous response to insulin indicates changes in its metabolic signaling, but normal insulin binding suggests that this alteration is a postreceptor event.
Glucose production, recycling, and gluconeogenesis in normals and diabetics: a mass isotopomer [U-13C]glucose study
Authors: Tayek J. A. , Katz J.
Published: December 2017

Eight normal controls and nine non-insulin-dependent diabetes mellitus diabetics were, after an overnight fast, infused for 3 h with [6-3H]- and with [U-13C]glucose with six 13C carbons at rates from 0.03 to 0.15 mg.kg-1.min-1. Plasma glucose and lactate were assayed by gas chromatography-mass spectroscopy. Several parameters of glucose metabolism were calculated from the mass isotopomer distribution. Glucose production (GP) determined with [6-3H]- and [U-13C]glucose agreed closely. GP was 1.9 +/- 0.16 (range 1.3-2.5) mg.kg-1.min-1 in controls and 2.8 +/- 0.29 (1.7-4.5) mg.kg-1.min-1 in diabetics (P < 0.05). The correlation in diabetes between plasma glucose and GP (r = 0.911, P < 0.01) was close. Recycling of carbon (8 vs 7%) dilution by unlabeled carbon (2- vs 2.3-fold), and dilution via the tricarboxylic acid cycle (1.5-fold) were similar in controls and diabetics. Gluconeogenesis was 0.90 +/- 0.08 (0.5-1.3) mg.kg-1.min-1 in controls and 1.30 +/- 0.13 (0.8-1.9) mg.kg-1.min-1 in diabetics (P < 0.05). Gluconeogenesis contributions to GP were 46.6 +/- 4.0% (26-61%) in the controls and 48.8 +/- 5.7% (32-83%) in diabetics. We show that, using [U-13C]glucose infusion of 2-5% of glucose turnover (0.03-0.10 mg.kg-1.min-1), a large number of parameters of glucose metabolism may be determined in humans.
Neural input modulates osmotically stimulated release of vasopressin into the supraoptic nucleus
Authors: Ludwig M. , Callahan M. F. , Landgraf R. , Johnson A. K. , Morris M.
Published: December 2017

The effects of lesioning of the anteroventral third ventricle (AV3V) region on vasopressin (VP) release into the supraoptic nucleus (SON) and blood in response to central and systemic osmotic stimulation were determined. Microdialysis probes were implanted bilaterally within the SON of male urethan-anesthetized rats with sham or AV3V lesions. Osmotic stimuli were administered intraperitoneally (3.5 M NaCl, 600 microliters/100 g body wt) and then via the microdialysis probes (1 M NaCl-artificial cerebrospinal fluid). AV3V lesions attenuated the response to systemic osmotic stimulation. The lesioned rats showed no increase in intranuclear VP release and reduced plasma VP (increase of 42.6 +/- 8.4 vs. 78.0 +/- 16.4 pg/ml) and blood pressure responses (7.1 +/- 2.3 vs. 19.6 +/- 3.2 mmHg) to intraperitoneal NaCl. In contrast, the endocrine and cardiovascular responses to direct osmotic stimulation of the nucleus were as seen in previous studies and seemed to be unaffected by the lesion. These results show that lesion of the AV3V region interrupts neuronal inputs which trigger VP secretion from the posterior pituitary as well as release into the extracellular compartment of the SON.
Physiological concentrations of insulin and T3 stimulate 3T3-L1 adipocyte acyl-CoA synthetase gene transcription
Authors: Kansara M. S. , Mehra A. K. , Von Hagen J. , Kabotyansky E. , Smith P. J.
Published: December 2017

Acyl-CoAsynthetase (ACS) is a key gene for cellular utilization of long-chain fatty acids. We characterized its regulation by physiological concentrations of insulin that acutely regulate metabolism. Our results demonstrate that subnanomolar insulin rapidly and maximally stimulates ACS gene transcription in the absence of protein synthesis; 0.5 nM insulin produced a 2.3 +/- 0.1-fold increase in ACS mRNA levels and induced ACS gene transcription 2.4 +/- 0.3-fold. The insulin sensitivity of ACS was compared with lipoprotein lipase (LPL) and stearoyl-CoA desaturase-1 (SCD-1), which were both less sensitive to insulin. Physiological triiodothyronine (10 nm) also induced ACS mRNA 2.4 +/- 0.1-fold and gene transcription 2.8 +/- 0.3-fold and coordinately induced LPL and SCD-1 mRNA and gene transcription. Because insulin and adenosine 3',5'-cyclic monophosphate often regulate genes involved in lipid and carbohydrate metabolism in a reciprocal manner, we evaluated effects of 1-methyl-3-isobutylxanthine (MIX).ACS mRNA levels were strongly downregulated by MIX in a dose-dependent manner, and ACS gene transcription inhibited in a coordinate manner with LPL and SCD-1. These data demonstrate a uniquely sensitive pattern of stimulation of ACS gene transcription by insulin with reciprocal regulation by MIX, and they suggest a significant role for ACS as a tightly regulated “gatekeeper” gene participating in the control of adipocyte metabolism.
Glucose tolerance and insulin action in healthy centenarians
Authors: Paolisso G. , Gambardella A. , Ammendola S. , D'Amore A. , Balbi V. , Varricchio M. , D'Onofrio F.
Published: December 2017

Advancing age has been found to be associated with a decline in insulin action. Nevertheless, no study has been conducted in healthy centenarians. Our study investigates glucose tolerance and insulin action in centenarians. Fifty-two subjects were enrolled. The subjects were divided in three groups as follows: 1) adults (< 50 yr; n = 20);2) aged subjects (> 75 yr; n = 22); and 3) centenarians (> 100 yr; n = 14). Body composition was studied by bioimpedance analysis. In all subjects, an oral glucose tolerance test and euglycemic glucose clamp were performed. Centenarians have a lower fat-free mass (FFM) than aged subjects and adults, whereas fasting plasma glucose, triglycerides, free fatty acids, urea, and creatinine were not different in the groups studies. Centenarians had a 2-h plasma glucose concentration (6.0 +/- 0.2 mmol/l) that was lower than that in aged subjects (6.6 +/- 0.5 mmol/l, P < 0.05) but not different from adults [6.4 +/- 0.4 mmol/l, P = not significant (NS)]. During the clamp, plasma glucose and insulin concentrations were similar in the three groups. In these conditions, centenarians had a whole body glucose disposal (34.1 +/- 0.6 mumol.kg FFM-1.min 1) that was greater than that in aged subjects (23.3 +/- 0.5 mumol.kg FFM-1.min-1 P < 0.01) but not different from adults (34.6 +/- 0.5 mumol/kg x min, P = NS). In conclusion, our study demonstrates that centenarians compared with aged subjects had a preserved glucose tolerance and insulin action.
Substrate and inhibitor specificity of the cloned human 11 beta-hydroxysteroid dehydrogenase type 2 isoform
Authors: Ferrari P. , Smith R. E. , Funder J. W. , Krozowski Z. S.
Published: December 2017

The 11 beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) enzyme is thought to confer specificity on the mineralocorticoid receptor by inactivating glucocorticoids in mineralocorticoid target organs. The cloned 11 beta HSD2 displayed Michaelis constant values for corticosterone and cortisol of 5.1 and 61 nM, respectively. Linearity in the dose-response curve ranged between 1 and 200 nM for corticosterone and 25 and 2,000 nM for cortisol, with no evidence for complex kinetics. Inhibition of cortisol oxidation by other steroids was purely competitive in nature. Inhibition of 11 beta HSD2 activity by the end product or aldosterone occurred only at supraphysiological levels, whereas corticosterone and deoxycorticosterone displayed significant inhibition at physiological concentrations and progesterone at concentrations that occur during pregnancy. In intact transfected CHOP cells, dexamethasone was converted to 11-dehydrodexamethasone by 11 beta HSD2 but not type 1 11 beta-hydroxysteroid dehydrogenase, an aspect that may be useful in evaluating 11 beta HSD activity in intact cells.
Effects of glucagon-like peptide-I on glucose turnover in rats
Authors: Van Dijk G. , Lindskog S. , Holst J. J. , Steffens A. B. , Ahren B.
Published: December 2017

The influences of glucagon-like peptide-I-(7-36) amide (GLP-I; 15 mumol. kg-1.min-1) on glucose turnover were studied in freely moving Wistar rats. In fed rats, GLP-1 reduced plasma glucose (from 7.3 +/- 0.2 to 5.6 +/- 0.3 mmol/l; P = 0.017), increased plasma insulin (from 20 +/- 3 to 89 +/- 11 mU/l; P = 0.002), and reduced plasma glucagon (from 44 +/- 1 to 35 +/- 2 pg/ml; P = 0.009) and glucose appearance rate (Ra; from 3.9 +/- 0.2 to 1.7 +/- 0.7 micromol.min-1. 100 g-1 after 30 min; P = 0.049) without affecting glucose disappearance rate (Rd). The glucose clearance rate (MCR) was increased (P = 0.048). In 48-h-fasted rats, GLP-I reduced plasma glucose (from 5.0 +/- 0.2 to 4.4 +/- 0.3 mmol/l; P = 0.035) and increased plasma insulin (from 4 +/- 1 to 25 +/- 10 mU/l; P = 0.042) and plasma glucagon (from 43 +/- 3 to 61 +/- 7 pg/ml; P = 0.046). Ra and Rd were not significantly affected, although Ra was lower than Rd after 15-30 min (P = 0.005) and MCR was increased (P = 0.049). Thus GLP-I reduces Ra in fed rats and increases MCR in fed and fasted rats. The reduced Ra seems mediated by an increased insulin-to-glucagon ratio; the increased glucose clearance seems dependent on insulin and a peripheral effect of GLP-I.
Reciprocal GLUT-1 and GLUT-4 expression and glucose transport in denervated muscles
Authors: Handberg A. , Megeney L. A. , McCullagh K. J. , Kayser L. , Han X. X. , Bonen A.
Published: December 2017

We investigated in 3-day-denervated muscles 1) the expression of GLUT-1 in perineurial sheaths (PNS) and muscle, 2) the muscle fiber-specific changes in GLUT-1 and GLUT-4, and 3) changes in basal and insulin-stimulated 3-O-methylglucose transport. GLUT-1 was increased in both the PNS (P < 0.05) and in the muscle membranes (P < 0.05). GLUT-1 and GLUT-4 concentrations were changed reciprocally, in a fiber-dependent fashion [GLUT-1: red gastrocnemius (RG), +31%; white gastrocnemius (WG), +10%; GLUT-4: RG, -53%; WG, -16%]. Basal glucose transport was increased (P < 0.05), and this increase was correlated with the oxidative nature of the muscles (r = 0.97). Insulin-stimulated glucose transport was decreased in denervated muscles (P < 0.05). This was also related to the oxidative nature of the muscles (r = -0.88). The increase in basal glucose transport was correlated with the loss of insulin-stimulated transport (r = 0.95). Thus the increase in GLUT-1 compensates for the loss of GLUT-4, resulting in a 56% regain of the reduced insulin-stimulated glucose transport.
Evidence for a circadian rhythm of insulin secretion
Authors: Boden G. , Ruiz J. , Urbain J. L. , Chen X.
Published: December 2017

Insulin secretion was studied in healthy volunteers at three different levels of glycemia. Plasma glucose was clamped at approximately 5, approximately 8.8 and approximately 12.6 mM for 68 h. Measured were serum insulin concentration and insulin secretion rates (ISR), the latter by deconvolution of plasma C-peptide concentration. Rhythmic patterns of ISR were identified (with a refined first-order Fourier transform) at all three glucose concentrations tested but were most clearly seen at 12.6 mM. ISR and serum insulin concentration changed in a circadian (approximately 24 h) rhythm, increasing from a nadir between midnight and 6 A.M. and reaching a peak between noon and 6 P.M. At 12.6 mM hyperglycemia, the amplitude of the insulin concentration cycles was greater than that of the ISR cycles (+/- 13.0 vs. +/- 8.7%) due to a decrease in insulin clearance (from 1.55 to 0.5 l/min, P < 0.01). Plasma melatonin levels (a marker of light-dark rhythmicity) changed in the opposite direction, i.e., they peaked when ISR bottomed and bottomed when ISR peaked. We concluded that normal human subjects have a circadian rhythm of insulin secretion, which becomes more apparent with rising ISR, and that circadian changes in ISR, rising during the day and falling during the night, may be one explanation for the well-established observation that glucose tolerance and insulin responses to glucose and meals are higher in the morning than at night.
Effects of long-term hypoxemia on pituitary-adrenal function in fetal sheep
Authors: Murotsuki J. , Gagnon R. , Matthews S. G. , Challis J. R.
Published: December 2017

To test the hypothesis that long-term hypoxemia causes premature activation of the fetal pituitary-adrenal function, we embolized the fetal side of the placenta in pregnant sheep and examined the changes in concentrations of immunoreactive adrenocorticotropic hormone (irACTH), cortisol, and prostaglandin E2 (PGE2) in fetal plasma, and levels and localization of proopiomelanocortin (POMC) mRNA in the pars distalis and the pars intermedia of the fetal pituitary. Twelve fetal sheep were studied (6 embolized and 6 control) for 21 days between 0.74 and 0.88 of gestation. Daily injections of nonradiolabeled microspheres were given into the fetal abdominal aorta to decrease fetal arterial oxygen content by 40-50% of the preembolization values. In the embolized group, concentrations of irACTH, PGE2, and cortisol in fetal plasma increased gradually and were significantly (P < 0.05) elevated above those of controls after day 10, day 16, and day 20, respectively. POMC mRNA levels in the pars distalis of the fetal pituitary were not different from those of controls but were significantly reduced in the pars intermedia (P < 0.05). We conclude that levels of POMC mRNA in the pars distalis are unchanged during long-term hypoxemia possibly because of negative feedback effects of elevated cortisol on the pituitary gland. During long-term fetal hypoxemia, there is a differential regulation of POMC mRNA expression in the pars distalis and pars intermedia.
Hormonal regulation of prostaglandin F2 alpha receptor gene expression in mouse ovary
Authors: Sugatani J. , Masu Y. , Nishizawa M. , Sakamoto K. , Houtani T. , Sugimoto T. , Ito S.
Published: December 2017

In this study we examined regulation by pituitary gonadotropins of the prostaglandin F2 alpha (PGF2 alpha) receptor gene expression in the mouse ovary. Administration of pregnant mare serum gonadotropin (PMSG) to 35-day-old mice in the diestrus phase stimulated the ovary and enhanced the production of progesterone at 1 h PMSG also increased the ovarian PGF2 alpha receptor mRNA level in a time-dependent manner, reaching a sixfold maximum at 1 h. These actions of PMSG were mimicked by human chorionic gonadotropin (hCG), follicle-stimulating hormone (FSH), and cholera toxin, all of which elevate intracellular adenosine 3',5'-cyclic monophosphate (cAMP). In situ hybridization revealed that PGF2 alpha receptor mRNA was localized to the corpus luteum, but the intensity of staining varied among corpora lutea in the same ovary. Exogenous PGF2 alpha inhibited the PMSG-stimulated progesterone production. These results demonstrate that gonadotropins may induce the expression of the PGF2 alpha receptor gene in luteal cells of the corpus luteum, probably by acting through a cAMP-mediated pathway, and that expression of the PGF2 alpha receptor may be functionally associated with the decrease in serum progesterone level.