bluuebunny/crossref_metadata_2025 huggingface dataset:
Adrenomedullin is a potent stimulator of osteoblastic activity in vitro and in vivo
Authors: Cornish Jillian , Callon Karen E. , Coy David H. , Jiang Ning-Yi , Xiao Liqun , Cooper Garth J. S. , Reid Ian R.
Published: December 2017

Adrenomedullin is a 52-amino acid vasodilator peptide produced in many tissues, including bone. It has 20% sequence identity with amylin, a regulator of osteoblast growth, and circulates in picomolar concentrations. The present study assesses whether adrenomedullin also acts on osteoblasts. At concentrations of 10−12 M and greater, adrenomedullin produced a dose-dependent increase in cell number and [3H]thymidine incorporation in cultures of fetal rat osteoblasts. This effect was also seen with adrenomedullin-(15—52), -(22—52), and -(27—52), but adrenomedullin-(40—52) was inactive. These effects were lost in the presence of amylin blockers, suggesting they were mediated by the amylin receptor. Adrenomedullin also increased [3H]thymidine incorporation into cultured neonatal mouse calvaria but, unlike amylin, did not reduce bone resorption in this model. Adrenomedullin stimulated phenylalanine incorporation into both isolated osteoblasts and calvaria. When injected daily for 5 days over the calvariae of adult mice, it increased indexes of bone formation two- to threefold ( P < 0.0001) and increased mineralized bone area by 14% ( P = 0.004). It is concluded that adrenomedullin regulates osteoblast function and that it increases bone mass in vivo. The potential of this family of peptides in the therapy of osteoporosis should be further evaluated.
Measurement of muscle protein degradation in live mice by accumulation of bestatin-induced peptides
Authors: Botbol Violeta , Scornik Oscar A.
Published: December 2017

Bestatin, an aminopeptidase inhibitor, permits the degradation of cellular proteins to di- and tripeptides but interferes with the further breakdown of these peptides to amino acids. We propose to measure instant rates of protein degradation in skeletal muscles of intact mice by the accumulation of bestatin-induced intermediates. Muscle protein was labeled by injection ofl-[guanidino-14C]arginine; 3 days later, maximum accumulation of intermediates was measured in abdominal wall muscles 10 min after the intravenous injection of 5 mg of bestatin. The peptides were partially purified and hydrolyzed in 6 N HCl, and the radioactivity in peptide-derived arginine was determined, after conversion to14CO2by treatment with arginase and urease. The measurement of bestatin-induced intermediates provides a unique tool for studying acute changes in muscle protein turnover in live mice. We observed a 62% increase in muscle protein breakdown after a 16-h fast, which was reversed by refeeding for 3.5 h, and a 38% increase after 3 days of protein depletion.
Effects of vagal blockade on the counterregulatory response to insulin-induced hypoglycemia in the dog
Authors: Jackson P. A. , Pagliassotti M. J. , Shiota M. , Neal D. W. , Cardin S. , Cherrington A. D.
Published: December 2017

Our aim was to determine whether vagal transmission is required for the hormonal response to insulin-induced hypoglycemia in 18-h-fasted conscious dogs. Hollow coils were placed around the vagus nerves, with animals under general anesthesia, 2 wk before an experiment. On the day of the study they were perfused with −15°C ethanol for the purpose of blocking vagal transmission, either coincident with the onset of insulin-induced hypoglycemia or after 2 h of established hypoglycemia. In a separate study the coils were perfused with 37°C ethanol in a sham cooling experiment. The following parameters were measured: heart rate, arterial plasma glucose, insulin, pancreatic polypeptide, glucagon, cortisol, epinephrine, norepinephrine, glycerol, free fatty acids, and endogenous glucose production. In response to insulin-induced hypoglycemia (42 mg/dl), plasma glucagon peaked at a level that was double the basal level, and plasma cortisol levels quadrupled. Plasma epinephrine and norepinephrine levels both rose considerably to 2,135 ± 314 and 537 ± 122 pg/ml, respectively, as did plasma glycerol (330 ± 60%) and endogenous glucose production (150 ± 20%). Plasma free fatty acids peaked at 150 ± 20% and then returned to basal levels by the end of the study. The hypoglycemia-induced changes were not different when vagal cooling was initiated after the prior establishment of hypoglycemia. Similarly, when vagal cooling occurred concurrently with the initiation of insulin-induced hypoglycemia (46 mg/dl), there were no significant differences in any of the parameters measured compared with the control. Thus vagal blockade did not prevent the effect on either the hormonal or metabolic responses to low blood sugar. Functioning vagal afferent nerves are not required for a normal response to insulin-induced hypoglycemia.
Effects of insulin-like growth factor I on glucose metabolism in rats with liver cirrhosis
Authors: Petersen Kitt Falk , Jacob Ralph , West A. Brian , Sherwin Robert S. , Shulman Gerald I.
Published: December 2017

To determine the effect of insulin-like growth factor I (IGF-I) on glucose metabolism in cirrhosis, a 2-h euglycemic clamp with IGF-I (0.65 nmol ⋅ kg−1⋅ min−1) or insulin (12 pmol ⋅ kg−1⋅ min−1) was performed in awake rats with carbon tetrachloride-induced liver cirrhosis. Rates of [3-3H]glucose-determined whole body glucose turnover were similar in the fasting state in cirrhotic and control rats (36.4 ± 2.6 and 37.7 ± 2.8 μmol ⋅ kg−1⋅ min−1, respectively). In the control group, IGF-I and insulin had similar effects on turnover (81.6 ± 27.0 and 76.1 ± 9.9 μmol ⋅ kg−1⋅ min−1), muscle glycogen synthesis (47.5 ± 12.3 and 37.5 ± 2.5 nmol ⋅ g muscle−1⋅ min−1), and suppression of endogenous glucose production (EGP; −54 ± 14 and −60 ± 12%). Cirrhotic rats were markedly insulin resistant, reflected by a 43% reduction of turnover (43.8 ± 9.4 μmol ⋅ g muscle−1⋅ min−1; P = 0.03), a 73% reduction in muscle glycogen synthesis (10.2 ± 3.4 nmol ⋅ g muscle−1⋅ min−1; P < 0.0001), and a diminished suppression of EGP (−32 ± 17% vs. control: −56 ± 14%; P < 0.05). In contrast, during the IGF-I clamps, turnover increased threefold in the cirrhotic rats ( P = 0.001), rates of muscle glycogen synthesis were 7.4 times higher than during the insulin stimulation ( P < 0.0001), and EGP was suppressed by 80 ± 12% ( P < 0.05). In conclusion, insulin resistance in cirrhotic rats is mostly due to defects in insulin-stimulated muscle glycogen synthesis, and the ability of IGF-I to stimulate muscle glycogen synthesis as well as suppress EGP is maintained in cirrhotic rats. These findings suggest that alterations in both hepatic and peripheral glucose metabolism in patients with cirrhosis might be amenable to IGF-I therapy.
Improved estimation of anaplerosis in heart using13C NMR
Authors: Cohen David M. , Bergman Richard N.
Published: December 2017

Anaplerotic enzymes, such as pyruvate carboxylase or malic enzyme, catalyze reactions that fill up the pools of the citric acid cycle (CAC), thereby increasing the total mass of CAC intermediates. Relative anaplerosis ( y) denotes the ratio of anaplerotic flux to the flux catalyzed by citrate synthase. We examine conventional methods [C. R. Malloy, A. D. Sherry, and F. M. H. Jeffrey. J. Biol. Chem. 263:6964–6971, 1988; C. R. Malloy, A. D. Sherry, and F. M. H. Jeffrey. Am. J. Physiol. 259 ( Heart Circ. Physiol. 28): H987–H995, 1990] of measurement of y using13C-labeled precursors and analysis of [13C]glutamate labeling by nuclear magnetic resonance (NMR) spectroscopy. Through mathematical analysis and computer simulation, we show that isotopic enrichment of the pool of pyruvate that is substrate for anaplerosis will severely decrease the accuracy of estimates of y made with conventional methods no matter how small the mass of the pool of pyruvate. Suppose that the recycling parameter R denotes the fraction of molecules of pyruvate that contain carbons derived from intermediates of the CAC. Each means of estimation of relative anaplerosis in the peer-reviewed literature assumes that R = 0, although this assumption has not been confirmed by experiment. We show that conventional formulas, using either fractional enrichments of carbons or isotopomer analysis, actually estimate at most y ⋅ (1 − R) instead of y during administration of [2-13C]acetate and unlabeled pyruvate. Using a new formula for estimation of y, we recalculate values of y from the literature and find them ∼50% too low. We assume that all anaplerosis is via pyruvate and that the difference in isotopic enrichment between cytosolic and mitochondrial malate is negligible.
Insulin secretion by gastrin-releasing peptide in mice: ganglionic versus direct islet effect
Authors: Karlsson Sven , Sundler Frank , Ahrén Bo
Published: December 2017

Gastrin-releasing peptide (GRP) stimulates insulin secretion by a direct islet effect. In this study, we initially demonstrated, by immunocytochemistry of the mouse pancreas, GRP immunoreactive nerve fibers within exocrine tissue, islets, and intrapancreatic ganglia. A more pronounced GRP innervation was found in ganglia compared with in islets. We therefore studied whether indirect cholinergic mechanisms contribute to the insulinotropic action of GRP. In mice, the insulinotropic response to GRP (4.25 nmol/kg iv) was inhibited by the m3-selective, muscarinic receptor antagonist 4-diphenylacetoxy- N-methyl piperidine methobromide (4-DAMP, 0.21 mol/kg; by 68%, P < 0.05) and by the ganglionic blocker hexamethonium (28 mol/kg; by 98%, P < 0.05). In contrast, in isolated islets, 4-DAMP or hexamethonium (10 or 100 μM) did not inhibit GRP (100 nM)-induced insulin secretion. Furthermore, afferent denervation by neonatal capsaicin did not affect the insulin response to GRP. We conclude that the insulinotropic effect of GRP in the mouse is mediated by both direct islet effects and through activation, at the ganglionic level, of postganglionic cholinergic nerves. In vivo, the indirect cholinergic mechanism predominates.
Production and utilization of amino acids by ovine placenta in vivo
Authors: Chung Misoo , Teng Cecilia , Timmerman Michelle , Meschia Giacomo , Battaglia Frederick C.
Published: December 2017

Uterine and umbilical uptakes of plasma amino acids were measured simultaneously in eighteen singleton pregnant ewes at 130 ± 1 days gestation for the purpose of establishing which amino acids are produced or used by the uteroplacenta under normal physiological conditions and at what rates. The branched-chain amino acids (BCAA) had uterine uptakes significantly greater than umbilical uptakes. Net uteroplacental BCAA utilization was 8.0 ± 2.5 μmol ⋅ kg fetus−1 ⋅ min−1( P < 0.005) and represented 42% of the total BCAA utilization by fetus plus uteroplacenta. There was placental uptake of fetal glutamate (4.2 ± 0.3 μmol ⋅ kg fetus−1 ⋅ min−1, P < 0.001) and no uterine uptake of maternal glutamate. Umbilical uptake of glutamine was ∼61% greater than uterine uptake, thus demonstrating net uteroplacental glutamine production of 2.2 ± 0.9 μmol ⋅ kg fetus−1 ⋅ min−1( P < 0.021). In conjunction with other evidence, these data indicate rapid placental metabolism of glutamate, which is in part supplied by the fetus and in part produced locally via BCAA transamination. Most of the glutamate is oxidized, and some is used to synthesize glutamine, which is delivered to the fetus. There was net uteroplacental utilization of maternal serine and umbilical uptake of glycine produced by the placenta. Maternal serine utilization and glycine umbilical uptake were virtually equal (3.14 ± 0.50 vs. 3.10 ± 0.46 μmol ⋅ kg fetus−1 ⋅ min−1). This evidence supports the conclusion that the ovine placenta converts large quantities of maternal serine into fetal glycine.
Role for parathyroid hormone in mechanical responsiveness of rat bone
Authors: Chow J. W. M. , Fox S. , Jagger C. J. , Chambers T. J.
Published: December 2017

We investigated the relationship between parathyroid hormone (PTH) and mechanical stimulation in mechanically induced osteogenesis. In normal rats, mechanical stimulation of the eighth caudal vertebra induced an osteogenic response. This was augmented by a single injection of human PTH-(1—34) 30–45 min before loading. No osteogenic response was seen in thyroparathyroidectomized (TPTX) rats; the osteogenic response was restored by a single injection of PTH before stimulation, suggesting that physiological levels of PTH are necessary for the mechanical responsiveness of bone. c- fosexpression was detected only in the osteocytes of those rats that were both mechanically stimulated and given PTH. This suggests that PTH supports mechanically induced osteogenesis by sensitizing either the strain-sensing mechanism itself or early responses of bone to strain-generated signals. The osteogenic response was not augmented by two further daily injections of PTH and was not seen in TPTX rats in which PTH administration was started 3 days after loading. These results reveal a major role for PTH in the mechanical responsiveness of rat bone.
Preexercise muscle glycogen content affects metabolism during exercise despite maintenance of hyperglycemia
Authors: Weltan Sandra M. , Bosch Andrew N. , Dennis Steven C. , Noakes Timothy D.
Published: December 2017

Trained cyclists with low muscle glycogen (LGH; n = 8) or normal glycogen (NGH; n = 5) exercised for 145 min at 70% of maximal oxygen uptake during a hyperglycemic clamp. Respiratory exchange ratio was higher in NGH than LGH, and free fatty acid concentrations were lower in NGH than LGH. Areas under the curve for insulin and lactate were lower in LGH than NGH. Total glucose infusion and total glucose oxidation were not different between NGH and LGH, and total glucose oxidation amounted to 65 and 66% of total glucose infusion in NGH and LGH, respectively. Rates of glucose oxidation rose during exercise, reaching peaks of 9.2 ± 1.7 and 8.3 ± 1.1 mmol/min in NGH and LGH, respectively. Muscle glycogen disappearance was greater in NGH than LGH. Thus 1) low muscle glycogen content does not cause increased glucose oxidation, even during hyperglycemia; instead there is an increase in fat oxidation, 2) there is an upper limit to the rate of glucose oxidation during exercise with hyperglycemia irrespective of muscle glycogen status, and 3) net muscle glycogen utilization is determined by muscle glycogen content at the start of exercise, even during hyperglycemia.
Contributions of theAmerican Journal of Physiologyto the discovery of insulin
Authors: Goldfine Ira D. , Youngren Jack F.
Published: December 2017

Since its inception in 1898 the American Journal of Physiology has been a leader in diabetes research and has published many key articles on the subject. The Journalfirst published studies of phlorhizin-induced diabetes in 1898, and after many other contributions went on to publish the first reports of Banting, Best, Macleod, and Collip in 1922 concerning the isolation and purification of insulin (5–8, 13). This review highlights some of these key contributions of the Journal.
A1adenosine receptor antagonism improves glucose tolerance in Zucker rats
Authors: Xu Baiyang , Berkich Deborah A. , Crist George H. , LaNoue Kathryn F.
Published: December 2017

The A1adenosine receptor (A1ar) antagonist 1,3-dipropyl-8-( p-acrylic)phenylxanthine (BW-1433) was administered to lean and obese Zucker rats to probe the influence of endogenously activated A1ars on whole body energy metabolism. The drug induced a transient increase in lipolysis as indicated by a rise in serum glycerol in obese rats. The disappearance of the response by day 7 of chronic studies was accompanied by an increase in A1ar numbers. Glucose tolerance tests were administered to rats treated with BW-1433. Peak serum insulin levels and areas under glucose curves (AUGs) were 34 and 41% lower in treated obese animals than in controls, respectively, and 19 and 39% lower in lean animals. With chronic administration (6 wk), AUGs decreased 47 and 33% in obese and lean animals, respectively. There was no effect of BW-1433 in either lean or obese rats on weight gain or percent body fat. Thus the major sustained influence of whole body A1ar antagonism in both lean and obese animals was an increase in whole body glucose tolerance at lower levels of insulin.
Effects of physical exercise on phospholipid fatty acid composition in skeletal muscle
Authors: Andersson Agneta , Sjödin Anders , Olsson Roger , Vessby Bengt
Published: December 2017

The effects of low-intensity exercise on the fatty acid composition in skeletal muscle and in serum were studied in 19 sedentary, middle-aged Swedish men. During a 10-wk period, all subjects were given a standardized diet with an identical fat composition. After 4 wk on this diet, they were randomly allocated to a daily exercise program (55% peak oxygen uptake) or to continue to live a sedentary life for the remaining 6 wk. Aerobic capacity (submaximal bicycle test) and peripheral insulin sensitivity (hyperinsulinemic euglycemic clamp) improved with training, whereas the body weight as well as the body composition (underwater weighing and bioimpedance) were unchanged. The proportions of palmitic acid (16:0) and linoleic acid [18:2(n-6)] and the sum of n-6 fatty acids [18:2(n-6), 20:3(n-6), 20:4(n-6)] were decreased in skeletal muscle phospholipids, whereas the proportion of oleic acid [18:1(n-9)] was increased, by training. The fatty acid profile in skeletal muscle triglycerides remained unchanged. We conclude that regular low-intensity exercise influences the fatty acid composition of the phospholipids in skeletal muscle, which hypothetically may contribute to changes of the skeletal muscle membrane fluidity and influence the peripheral insulin sensitivity.
Brown fat is essential for cold-induced thermogenesis but not for obesity resistance in aP2-Ucp mice
Authors: Stefl Bohumír , Janovská Alena , Hodný Zdenek , Rossmeisl Martin , Horáková Milada , Syrový Ivo , Bémová Jaroslava , Bendlová Bela , Kopecký Jan
Published: December 2017

The role of brown adipose tissue in total energy balance and cold-induced thermogenesis was studied. Mice expressing mitochondrial uncoupling protein 1 (UCP-1) from the fat-specific aP2 gene promoter (heterozygous and homozygous aP2 -Ucp transgenic mice) and their nontransgenic C57BL6/J littermates were used. The transgenic animals are resistant to obesity induced by a high-fat diet, presumably due to ectopic synthesis of UCP-1 in white fat. These animals exhibited atrophy of brown adipose tissue, as indicated by smaller size of brown fat and reduction of its total UCP-1 and DNA contents. Norepinephrine-induced respiration (measured in pentobarbital sodium-anesthetized animals) was decreased proportionally to the dosage of the transgene, and the homozygous (but not heterozygous) transgenic mice exhibited a reduction in their capacity to maintain body temperature in the cold. Our results indicate that the role of brown fat in cold-induced thermogenesis cannot be substituted by increased energy expenditure in other tissues.
Measurement of dermal collagen synthesis rate in vivo in humans
Authors: El-Harake Wassim A. , Furman Mikhail A. , Cook Brian , Nair K. Sreekumaran , Kukowski Jayme , Brodsky Irwin G.
Published: December 2017

Accumulation of collagen produces organ dysfunction in many pathological conditions. We measured the fractional synthesis rate (FSR) of dermal collagen in five human volunteers from the increment of [13C]proline in detergent-soluble dermal collagen hydroxylated to hydroxyproline during a continuous infusion ofl-[1-13C]proline. In these and eight other volunteers, we measured [13C]proline enrichment in skin aminoacyl-tRNA, skin tissue fluid amino acid, and plasma. The prolyl-[13C]tRNA enrichment was one-half that in tissue fluid proline and more than threefold less than in plasma. The FSR of dermal collagen was 0.076 ± 0.063%/h (mean ± SD), similar to previously reported rates for skeletal muscle contractile proteins and substantially slower than hepatically derived circulating proteins such as albumin or fibrinogen. We conclude that the FSR of human dermal collagen resembles that of other human proteins considered to display slow turnover. The current method for its measurement may be used to determine the regulation of collagen synthesis in other organs and disease states.
Whole body and splanchnic metabolic, circulatory, and thermal effects of oral vs. intravenous fat administration
Authors: Brundin Tomas
Published: December 2017

Relatively few studies on the physiological effects of fat administration have been published. In the present study, whole body and splanchnic oxygen consumption, blood flow, blood temperature, glucose and insulin economy, and arterial and hepatic venous concentrations of hemoglobin, free fatty acids (FFA), and glycerol were measured by indirect calorimetry and catheterization technique in seven healthy men before and during 2.5 h after oral ingestion of 850 kJ of fat and in five healthy men before and during a 2.5-h intravenous (iv) infusion of 850 kJ of fat. Oral fat increased the splanchnic blood flow by 57 ± 25%, reduced the plasma volume by 6 ± 1%, reduced the arterial concentrations of FFA and glycerol by 33 ± 7 and 50 ± 16%, respectively, and increased arterial insulin concentration by 52 ± 12% despite a simultaneous reduction in splanchnic insulin release, thus suggesting a reduction of the extrasplanchnic extraction of insulin. None of these effects occurred during intravenous fat infusion, and it is suggested that intestinal hormones might elicit these effects. Body heat content, unaffected after oral fat, increased by 67 ± 20 kJ during intravenous fat infusion.
Evidence against a role for the growth hormone-releasing peptide axis in human slow-wave sleep regulation
Authors: Moreno-Reyes Rodrigo , Kerkhofs Myriam , L’Hermite-Balériaux Mireille , Thorner Michael O. , Van Cauter Eve , Copinschi Georges
Published: December 2017

A complex interrelationship exists between sleep and somatotropic activity. In humans, intravenous injections of growth hormone-releasing hormone (GHRH) given during sleep consistently stimulate slow-wave (SW) sleep, particularly when given in the latter part of the night. In the present study, the possible somnogenic effects induced under similar conditions by GH-releasing peptide (GHRP) were investigated in seven young healthy men. Bolus intravenous injections of GHRP-2 (1 μg/kg body wt) or saline, in randomized order, were given after 60 s of the third rapid-eye-movement period. All GHRP injections were immediately followed by transient prolactin elevations and by GH pulses of a magnitude within or around the upper limit of the physiological range. Except for a nonsignificant tendency to increased amounts of wakefulness during the 1st h after the injection, no effects of GHRP-2 administration on sleep were detected. There was in particular no enhancement of SW sleep. Thus, in contrast to GHRH, late-night single injections of GHRP-2 at a dosage resulting in similar GH elevations have no stimulatory effects on SW sleep. The present data provide evidence against the involvement of the GHRP axis in human SW sleep regulation.
Training-induced alterations in fat and carbohydrate metabolism during exercise in elderly subjects
Authors: Sial Shahid , Coggan Andrew R. , Hickner Robert C. , Klein Samuel
Published: December 2017

Compared with young adults, fat oxidation is lower in elderly persons during endurance exercise performed at either the same absolute or relative intensity. We evaluated the effect of 16 wk of endurance training on fat and glucose metabolism during 60 min of moderate intensity exercise [50% of pretraining peak oxygen consumption (V˙o2 peak)] in six elderly men and women (74 ± 2 yr). Training caused a 21% increase in meanV˙o2 peak. The average rate of fat oxidation during exercise was greater after (221 ± 28 μmol/min) than before (166 ± 17 μmol/min) training ( P = 0.002), and the average rate of carbohydrate oxidation during exercise was lower after (3,180 ± 461 μmol/min) than before (3,937 ± 483 μmol/min) training ( P = 0.003). Training did not cause a significant change in glycerol rate of appearance (Ra), free fatty acid (FFA) Ra, and FFA rate of disappearance during exercise. However, glucose Raduring exercise was lower after (1,027 ± 95 μmol/min) than before (1,157 ± 69 μmol/min) training ( P = 0.01). These results demonstrate that a 16-wk period of endurance training increases fat oxidation without a significant change in lipolysis (glycerol Ra) or FFA availability (FFA Ra) during exercise in elderly subjects. Therefore, the training-induced increase in fat oxidation during exercise is likely related to alterations in skeletal muscle fatty acid metabolism.
Glucose-induced pulsatile insulin release from single islets at stable and oscillatory cytoplasmic Ca2+
Authors: Bergsten Peter
Published: December 2017

The cytoplasmic Ca2+concentration ([Ca2+]i) and insulin release were measured simultaneously in mouse pancreatic islets cultured overnight. [Ca2+]iwas 105 nM and insulin release 3 pmol ⋅ g−1⋅ s−1at 3 mM glucose. An increase to 7 mM glucose reduced [Ca2+]itransiently, whereas insulin release doubled and was pulsatile with a frequency of 0.47 min−1. [Ca2+]ioscillations with similar frequency appeared at 11 mM glucose associated with increased amplitude of the insulin oscillations, raising the secretory rate 10-fold. In the presence of 16 and 20 mM glucose [Ca2+]iwas >300 nM and showed no oscillations apart from two islets, which demonstrated [Ca2+]ioscillations with small amplitude at 16 mM glucose. Insulin release with maintained frequency increased by 46 and 31%, respectively. When the glucose concentration was increased from 3 to 11 mM, [Ca2+]idecreased with a nadir that appeared significantly earlier than when the glucose concentration was raised from 3 to 7 mM. Glucose-induced insulin release from the isolated islet is pulsatile both at stable and oscillatory [Ca2+]i, with changes in secretory rate caused by the sugar also when [Ca2+]iis unchanged.
Distribution and kinetics of amylin in humans
Authors: Clodi M. , Thomaseth K. , Pacini G. , Hermann K. , Kautzky-Willer A. , Waldhäusl W. , Prager R. , Ludvik B.
Published: December 2017

The aim of the study was to determine the apparent volume of distribution (VTOT), total body clearance (CL), fractional clearance, and mean residence time (MRT) of the β-cell hormone amylin. We therefore performed an intravenous injection of 50 μg of human synthetic amylin (amlintide) in nine healthy male subjects during suppression of endogenous amylin release by intravenous somatostatin (0.06 μg ⋅ kg−1⋅ min−1). The plasma levels of amylin concentrations over time were analyzed using three-exponential curves. VTOTwas 173 ± 16 ml/kg and was not different from that of insulin reported in the literature (157 ml/kg). MRT was 27.7 ± 2.1 min and thus two times the reported value for insulin (14.1 min) and C-peptide (16.4 min). CL and fractional CL were 6.2 ± 0.2 ml ⋅ kg−1⋅ min−1and 0.038 ± 0.003 min−1, respectively. Fractional CL is therefore definitely lower than that reported for insulin (0.12–0.2 min−1) but is, however, in the range of that of C-peptide (0.05 min−1). In conclusion, clearance of amylin is similar to that reported for C-peptide and much slower than insulin, indicating that the commonly used molar insulin-to-amylin ratio does not reflect the correct relationship of the two peptides.
Mechanisms involved in the protective effect of estradiol-17β on lipid peroxidation and DNA damage
Authors: Ayres Stacey , Abplanalp William , Liu James H. , Subbiah M. T. Ravi
Published: December 2017

Previous studies from our laboratory have shown that estrogens can protect against lipoprotein peroxidation and DNA damage. In this study, the mechanism of estradiol-17β (E2) action was investigated by comparing E2with selective scavengers of reactive oxygen species (ROS) in terms of inhibition of 1) human low-density lipoprotein (LDL) peroxidation (measured by the diene conjugation method) and 2) DNA damage (measured by the formation of strand breaks in supercoiled OX-174 RFI DNA). In addition, the direct effect of E2on the generation of individual ROS was also measured. By use of ROS scavengers, it was determined that lipoprotein peroxidation was predominantly due to superoxide (39%), with some contributions from hydrogen peroxide (23%) and peroxy (38%) radicals. E2was a more effective inhibitor of peroxidation than all the ROS scavengers combined. In DNA damage, scavengers of hydrogen peroxide, hydroxyl, and superoxide radical offered significant protection (49–65%). E2alone offered a similar degree of protection, and no additional effect was evident when it was combined with ROS scavengers. E2caused a significant reduction (37%) in the production of superoxide radical by bovine heart endothelial cells in culture but had no effect on the formation of either hydrogen peroxide or hydroxyl radicals. These studies show that 1) the protection offered by E2in terms of lipid peroxidation could be due to its ability to inhibit generation of superoxide radical and prevent further chain propagation, and 2) in DNA damage protection, E2mainly appears to inhibit chain propagation.
Steroid specificity of the putative DHB receptor: evidence that the receptor is not 11βHSD
Authors: Sheppard Karen E. , Khoo Karen , Krozowski Zygmunt S. , Li Kevin X. Z.
Published: December 2017

Recently, we identified a novel putative nuclear receptor in colonic crypt cells distinct from both mineralocorticoid receptor and glucocorticoid receptor, with high affinity for 11-dehydrocorticosterone (11-DHB) (33). In the present study, competitive nuclear binding assays demonstrated that this site has a unique steroid binding specificity that distinguishes it from other steroid receptors. Western blot analysis showed the presence of 11β-hydroxysteroid dehydrogenase-2 (11βHSD2) but not 11βHSD1in colonic crypt cells and showed that 11βHSD2was present in the nuclear pellet. Differences in steroid specificity between the putative DHB receptor and inhibition of 11βHSD activity indicate that binding is not to the enzyme. Furthermore, modified Chinese hamster ovary cells transfected with the 11βHSD2gene express nuclear 11βHSD2but not a nuclear DHB binding site. In conclusion, these data support the existence of a novel nuclear DHB receptor in rat colon that is distinct from the classic steroid receptors and from both 11βHSD1and 11βHSD2.
Effects of short-term submaximal training in humans on muscle metabolism in exercise
Authors: Putman C. T. , Jones N. L. , Hultman E. , Hollidge-Horvat M. G. , Bonen A. , McConachie D. R. , Heigenhauser G. J. F.
Published: December 2017

Muscle metabolism, including the role of pyruvate dehydrogenase (PDH) in muscle lactate (Lac−) production, was examined during incremental exercise before and after 7 days of submaximal training on a cycle ergometer [2 h daily at 60% peak O2 uptake (V˙o 2 max)]. Subjects were studied at rest and during continuous steady-state cycling at three stages (15 min each): 30, 65, and 75% of the pretraining V˙o 2 max. Blood was sampled from brachial artery and femoral vein, and leg blood flow was measured by thermodilution. Biopsies of the vastus lateralis were obtained at rest and during steady-state exercise at the end of each stage. V˙o 2 max, leg O2 uptake, and the maximum activities of citrate synthase and PDH were not altered by training; muscle glycogen concentration was higher. During rest and cycling at 30% V˙o 2 max, muscle Lac− concentration ([Lac−]) and leg efflux were similar. At 65%V˙o 2 max, muscle [Lac−] was lower (11.9 ± 3.2 vs. 20.0 ± 5.8 mmol/kg dry wt) and Lac− efflux was less [−0.22 ± 0.24 (one leg) vs. 1.42 ± 0.33 mmol/min] after training. Similarly, at 75%V˙o 2 max, lower muscle [Lac−] (17.2 ± 4.4 vs. 45.2 ± 6.6 mmol/kg dry wt) accompanied less release (0.41 ± 0.53 vs. 1.32 ± 0.65 mmol/min) after training. PDH in its active form (PDHa) was not different between conditions. Calculated pyruvate production at 75%V˙o 2 max fell by 33%, pyruvate reduction to lactate fell by 59%, and pyruvate oxidation fell by 24% compared with before training. Muscle contents of coenzyme A and phosphocreatine were higher during exercise after training. Lower muscle lactate production after training resulted from improved matching of glycolytic and PDHafluxes, independently of changes in muscle O2 consumption, and was associated with greater phosphorylation potential.
Age-related increase in mitochondrial proton leak and decrease in ATP turnover reactions in mouse hepatocytes
Authors: Harper Mary-Ellen , Monemdjou Shadi , Ramsey Jon J. , Weindruch Richard
Published: December 2017

Age-related changes in mitochondria, including decreased respiratory control ratios and altered mitochondrial inner membrane lipid composition, led us to study oxidative phosphorylation in hepatocytes from old (30 mo) and young (3 mo) male C57BL/J mice. Top-down metabolic control analysis and its extension, elasticity analysis, were used to identify changes in the control and regulation of the three blocks of reactions constituting the oxidative phosphorylation system: substrate oxidation, mitochondrial proton leak, and the ATP turnover reactions. Resting oxygen consumption of cells from old mice was 15% lower ( P < 0.05) than in young cells. This is explained entirely by a decrease in oxygen consumption supporting ATP turnover reactions. At all values of mitochondrial membrane potential assessed, the proportion of total oxygen consumption used to balance the leak was greater in the old cells than in the young cells. Metabolic control coefficients indicate a shift in control over respiration and phosphorylation away from substrate oxidation toward increased control by leak and by ATP turnover reactions. Control of the actual number of ATP molecules synthesized by mitochondria for each oxygen atom consumed by the ATP turnover and leak reactions was greater in old than in young cells, showing that efficiency in older cells is more sensitive to changes in these two blocks of reactions than in young cells.
Gi-3protein mediates the increase in voltage-gated K+currents by somatostatin on cultured ovine somatotrophs
Authors: Chen Chen
Published: December 2017

Voltage-gated K+currents in rat somatotrophs are increased by somatostatin (SRIF) through unidentified G protein. In this experiment, somatotroph-enriched cells (up to 85%) were obtained from ovine pituitary glands and further identified by the increase in K+currents by SRIF. The whole cell recording was employed to study the voltage-gated K+currents. A reversible increase in K+currents (up to 150% of control) was obtained in response to local application of SRIF (10 nM) but not vehicle. When the guanosine 5′- O-(3-thiotriphosphate) was included in the pipette solution (200 μM), the recovery phase of K+current response to SRIF was abolished. Inclusion of guanosine 5′- O-(2-thiodiphosphate) (200 μM) in pipette solution blocked the K+current response to SRIF. Intracellular dialysis of antibodies against αo-, αi-, αi-1–2-, or αi-3-subunits of G proteins via patch pipettes was confirmed by immunofluorescent staining of the antibodies. Antibody dialysis alone did not modify voltage-gated K+currents. Dialysis of anti-αior anti-αi-3antibodies significantly attenuated the increase in K+currents that was obtained after application of 10 or 100 nM SRIF. Dialysis with anti-αo, anti-αi-1–2, or heat-inactivated (60°C for 10 min) anti-αiantibodies did not diminish the effect of SRIF on K+currents. We conclude that the Gi-3protein mediates the effect of SRIF on voltage-gated K+currents in ovine somatotrophs.
Plasminogen binds the heparin-binding domain of insulin-like growth factor-binding protein-3
Authors: Campbell Phil G. , Durham Susan K. , Suwanichkul Adisak , Hayes James D. , Powell David R.
Published: December 2017

Limited proteolysis lowers affinity of insulin-like growth factor (IGF)-binding protein (IGFBP)-3 for bound IGFs, resulting in greater IGF bioavailability. Plasmin is one of many proteases that cleave IGFBP-3, and the plasmin system may regulate IGFBP-3 proteolysis and IGF bioavailability in cultured cells in vitro. A role for the plasmin system in IGFBP-3 proteolysis in vivo is suggested by data presented here showing that IGFBP-3 binds plasminogen (Pg; Glu-Pg) with a dissociation constant ( Kd) ranging from 1.43 to 3.12 nM. IGF-I and Glu-Pg do not compete for IGFBP-3 binding; instead, the binary IGFBP-3/Glu-Pg complex binds IGF-I with high affinity ( Kd= 0.47 nM) to form a ternary complex. Competitive binding studies suggest that the kringle 1, 4, and 5 domains of Glu-Pg and the heparin-binding domain of IGFBP-3 participate in forming the IGFBP-3/Glu-Pg complex, and other studies show that Glu-Pg in this complex is activated at a normal rate by tissue Pg activator. Importantly, IGFBP-3/Glu-Pg complexes were detected in both human citrate plasma and serum, indicating that these complexes exist in vivo. Binding of IGFBP-3 to Glu-Pg in vivo suggests how Glu-Pg activation can specifically lead to IGFBP-3 proteolysis with subsequent release of IGFs to local target tissues.
Differential regulation of skeletal muscle protein turnover by insulin and IGF-I after bacteremia
Authors: Vary Thomas C. , Dardevet Dominique , Grizard Jean , Voisin Laure , Buffiere Caroline , Denis Phillipe , Breuille Denis , Obled Christiane
Published: December 2017

Skeletal muscle catabolism is a characteristic metabolic response to sepsis. We investigated the ability of physiological insulin (2 nM) or insulin-like growth factor I (IGF-I, 10 nM) concentrations to modify protein metabolism during incubation of epitrochlearis 2, 6, or 15 days after injection of live Escherichia coli. On days 2 and 6 postinfection, skeletal muscle exhibited an exacerbated negative protein balance resulting from both an inhibition in protein synthesis (25%) and an enhanced proteolysis (90%) compared with controls. By day 15 postinfection, protein balance in infected rats was significantly improved compared with either day 2 or 6. At this time, protein synthesis was augmented and protein degradation was decreased in infected rats relative to day 6. Insulin or IGF-I stimulated protein synthesis in muscles from septic and control rats in vitro to the same extent at each time point examined. The ability of insulin or IGF-I to limit protein degradation was severely blunted 48 h after infection. On day 6 postinfection, the effect of insulin or IGF-I to inhibit proteolysis was more pronounced than on day 2. Incubation with IGF-I limited proteolysis to a greater extent than insulin on both days in infected but not control rats. By day 15, insulin diminished proteolysis to the same extent as in controls. The results suggest that injection of bacteria causes fundamental derangements in protein metabolism that persist for days after infection.
Systemic administration of amylin increases bone mass, linear growth, and adiposity in adult male mice
Authors: Cornish Jillian , Callon Karen E. , King Alan R. , Cooper Garth J. S. , Reid Ian R.
Published: December 2017

Amylin is a peptide hormone cosecreted with insulin from the pancreatic β-cells that can act as an osteoblast mitogen and as an inhibitor of bone resorption. The effects on bone of its systemic administration are uncertain. The present study addresses this question in adult male mice that were given daily subcutaneous injections of amylin (10.5 μg) or vehicle ( n = 20 in each group) for 4 wk. Histomorphometric indices of bone formation increased 30–100% in the amylin-treated group, whereas resorption indices were reduced by ∼70% ( P < 0.005 for all indices). Total bone volume in the proximal tibia was 13.5 ± 1.4% in control animals and 23.0 ± 2.0% in those receiving amylin ( P = 0.0005). Cortical width, tibial growth plate width, tibial length, body weight, and fat mass were all increased in the amylin-treated group. It is concluded that systemic administration of amylin increases skeletal mass and linear bone growth. This peptide has potential as a therapy for osteoporosis if its bone effects can be dissociated from those on soft tissue mass.
Intrinsic mineralization defect inHyp mouse osteoblasts
Authors: Xiao Z. S. , Crenshaw M. , Guo R. , Nesbitt T. , Drezner M. K. , Quarles L. D.
Published: December 2017

X-linked hypophosphatemia (XLH) is caused by inactivating mutations of PEX, an endopeptidase of uncertain function. This defect is shared by Hyp mice, the murine homologue of the human disease, in which a 3′ Pex deletion has been documented. In the present study, we report that immortalized osteoblasts derived from the simian virus 40 (SV40) transgenic Hyp mouse (TMOb- Hyp) have an impaired capacity to mineralize extracellular matrix in vitro. Compared with immortalized osteoblasts from the SV40 transgenic normal mouse (TMOb-Nl), osteoblast cultures from the SV40 Hyp mouse exhibit diminished 45Ca accumulation into extracellular matrix (37 ± 6 vs. 1,484 ± 68 counts ⋅ min−1 ⋅ μg protein−1) and reduced formation of mineralization nodules. Moreover, in coculture experiments, we found evidence that osteoblasts from the SV40 Hyp mouse produce a diffusible factor that blocks mineralization of extracellular matrix in normal osteoblasts. Our findings indicate that abnormal PEX in osteoblasts is associated with the accumulation of a factor(s) that inhibits mineralization of extracellular matrix in vitro.
Splanchnic retention of intraduodenal and intrajejunal glucose in healthy adults
Authors: Livesey G. , Wilson P. D. G. , Roe M. A. , Faulks R. M. , Oram L. M. , Brown J. C. , Eagles J. , Greenwood R. H. , Kennedy H.
Published: December 2017

Estimates of the spanchnic retention and appearance in the systemic circulation of orally administered glucose vary among laboratories even after recently identified sources of error have been accounted for [Livesey, G., P. D. G. Wilson, J. R. Dainty, J. C. Brown, R. M. Faulks, M. A. Roe, T. A. Newman, J. Eagles, F. A. Mellon, and R. Greenwood. Am. J. Physiol. 275 ( Endocrinol. Metab. 38): E717–E728, 1998]. We questioned whether, in healthy humans,d-glucose delivered intraluminally to the midjejunum appeared systemically as extensively as that delivered intraduodenally. Subjects were infused over a period of 90 min with 50 g of glucose in 1 liter of isotonic saline (incorporating 0.5 gd-[13C6]glucose) per 70 kg of body weight. Infusions were via enteral tubes terminating ∼15 and 100 cm postpylorus. The systemic appearance of glucose was monitored by means of a primed-continuous intravenous infusion ofd-[6,6-2H2]glucose. Whereas 98 ± 2% ( n = 7) of the duodenally infused glucose appeared in the systemic circulation, only 35 ± 9% ( n = 7) of midjejunally infused glucose did so, implying that 65 ± 9% was retained in the splanchnic bed. Either glucose was less efficiently absorbed at the midintestinal site or hepatic glucose sequestration was increased 10-fold, or both. The proximal intestine plays a key role in the delivery of glucose to the systemic circulation, and the distal intestine potentially delivers more glucose to the liver.
Age effect on fibrinogen and albumin synthesis in humans
Authors: Fu Aizhong , Nair K. Sreekumaran
Published: December 2017

A strong association has been reported between atherosclerotic diseases and fibrinogen levels, and a decreased whole body protein synthesis has also been reported with aging. We investigated the effect of age on fractional synthesis rates (FSR) of fibrinogen and albumin in 12 human subjects of young (20–30 yr), middle (45–60 yr), and old (65–79 yr) age by use ofl-[1-13C]leucine andl-[15N]phenylalanine as tracers. An age-related decline in FSR of fibrinogen ( P < 0.01) was observed with use of both tracers, with the maximal decrease (average 37% with α-[13C]ketoisocaproate as the precursor) occurring by middle age and with no further changes thereafter. In contrast, plasma concentrations of fibrinogen increased with age ( P < 0.002). There was no age-related change in synthesis rate and concentrations of albumin. An age-related decline in fibrinogen FSR, but not FSR of albumin, indicates a differential effect of age on synthesis rate of these two liver proteins. This study also demonstrated that the increased circulating levels of fibrinogen represent a slower rate of disposal of fibrinogen rather than an increased production rate.
Isolation of human skeletal muscle myosin heavy chain and actin for measurement of fractional synthesis rates
Authors: Hasten D. L. , Morris G. S. , Ramanadham S. , Yarasheski K. E.
Published: December 2017

Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), we have developed a simple method to isolate myosin heavy chain (MHC) and actin from small (60–80 mg) human skeletal muscle samples for the determination of their fractional synthesis rates. The amounts of MHC and actin isolated are adequate for the quantification of [13C]leucine abundance by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Fractional synthesis rates of mixed muscle protein (MMP), MHC, and actin were determined in six healthy young subjects (27 ± 1 yr) after they received a 14-h intravenous infusion (prime = 7.58 μmol/kg body wt, constant infusion = 7.58 μmol ⋅ kg body wt−1 ⋅ h−1) of [1-13C]leucine. The fractional synthesis rates of MMP, MHC, and actin were found to be 0.0468 ± 0.0048, 0.0376 ± 0.0033, and 0.0754 ± 0.0078%/h, respectively. Overall, the synthesis rate of MHC was 20% lower ( P = 0.012), and the synthesis rate of actin was 61% higher ( P = 0.060, not significant) than the MMP synthesis rate. The isolation of these proteins for isotope abundance analysis by GC-C-IRMS provides important information about the synthesis rates of these specific contractile proteins, as opposed to the more general information provided by the determination of MMP synthesis rates.
β-Adrenergic regulation of lipolysis and blood flow in human skeletal muscle in vivo
Authors: Hagström-Toft Eva , Enoksson Staffan , Moberg Erik , Bolinder Jan , Arner Peter
Published: December 2017

Little is known about the regulation of catecholamine-stimulated lipolysis in human skeletal muscle. Therefore, β-adrenergic regulation of lipolysis and blood flow was investigated in healthy subjects in vivo by use of microdialysis of the gastrocnemius muscle. First, during a hypoglycemic, hyperinsulinemic clamp, which induces a lipolytic response in skeletal muscle tissue, the muscle was locally perfused with β-adrenoceptor blocking agents. Perfusion with nonselective (propranolol) and β2-selective (ICI-118551) blocking agents counteracted the hypoglycemia-induced lipolysis ( P < 0.01), but perfusion with metoprolol (β1-blocker) did not affect the glycerol response. Second, selective β-adrenoceptor agonists were perfused in situ into skeletal muscle during resting conditions. β2-Adrenoceptor stimulation with terbutaline induced a concentration-dependent increase in skeletal muscle glycerol levels and in tissue blood flow, whereas perfusion with β1- or β3-adrenoceptor agonists (dobutamine or CGP-12177) did not influence the glycerol concentration or blood flow. In conclusion, in skeletal muscle tissue, only the β2-subtype is of importance among β-adrenoceptors for regulation of lipolysis and blood flow. This is in contrast to adipose tissue, where β1- and β3-adrenoceptors are also involved.