bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatty acid oxidation is directly regulated by carbohydrate metabolism during exercise
Authors: Coyle E. F. , Jeukendrup A. E. , Wagenmakers A. J. , Saris W. H.
Published: December 2017

We determined whether increased glycolytic flux from hyperglycemia and hyperinsulinemia directly reduces fatty acid oxidation during exercise. Fatty acid oxidation rates were measured during constant-rate intravenous infusion of trace amounts of a long-chain fatty acid ([1-13C]palmitate; Pal) vs. a medium-chain fatty acid ([1-13C]octanoate; Oct). Six endurance-trained men cycled for 40 min at 50% of maximal O2 uptake 1) after an overnight fast (“fasting”) and 2) after ingestion of 1.4 g/kg of glucose at 60 min and again 10 min before exercise (Glc). Glc caused hyperinsulinemia, a preexercise blood glucose of 6 mM, and a 34% reduction in total fat oxidation during exercise due to an approximately equal reduction in oxidation of plasma-free fatty acids (FFA) and intramuscular triglycerides (all P < 0.05). Oxidation of Pal was significantly reduced during Glc compared with fast (i.e., 70.0 +/- 4.1 vs. 86.0 +/- 1.9% of tracer infusion rate; P < 0.05). However, Glc had no effect on Oct oxidation, which is apparently not limited by mitochondrial transport. Furthermore, Glc reduced plasma FFA appearance 36% (P < 0.05), indicating a coordination of effects on adipose tissue and muscle. In summary, substrate oxidation during exercise can be regulated by increased glycolytic flux that is accompanied by a direct inhibition of long-chain fatty acid oxidation. These observations indicate that carbohydrate availability can directly regulate fat oxidation during exercise.
Regulation of glucose production during exercise at 80% of VO2peak in untrained humans
Authors: Coggan A. R. , Raguso C. A. , Gastaldelli A. , Williams B. D. , Wolfe R. R.
Published: December 2017

To determine whether alterations in insulin and/or glucagon secretion play an important role in stimulating glucose production (Ra) during intense but submaximal exercise, we studied six untrained subjects during 30 min of cycling at 80% of peak oxygen uptake on two occasions: once under control conditions and once when alterations in insulin and glucagon secretion were prevented with the use of the pancreatic islet clamp technique. In the latter experiments, glucose was infused during exercise to match glycemia with control levels. Glucose kinetics were measured in both trials using a primed, continuous infusion of [6,6-2H]glucose. In the control trial, glucose Ra rose from 11.9 +/- 0.8 mumol.min-1.kg-1 at rest to 42.5 +/- 4.3 mumol.min-1.kg-1 by the end of exercise. A similar increment was observed in the islet clamp experiments, with endogenous Ra peaking at 37.2 +/- 7.9 mumol.min-1.kg-1. This was true even through glucagon concentration did not change from basal and insulin concentration actually rose (the latter apparently due to a decrease in insulin clearance during intense exercise). Thus neither decrements in insulin or increments in glucagon are apparently required to stimulate glucose Ra under the present conditions. Because epinephrine levels rose only slightly, it appears that either neurally released norepinephrine or some other, as yet unidentified, factor is responsible for stimulating glucose Ra during intense but submaximal exercise.
Diabetic RBC-induced oxidant stress leads to transendothelial migration of monocyte-like HL-60 cells
Authors: Rattan V. , Shen Y. , Sultana C. , Kumar D. , Kalra V. K.
Published: December 2017

Red blood cells (RBC) from patients with diabetes mellitus exhibit an increased propensity to adhere to cultured human umbilical vein endothelial cells (HUVEC) as a result of interaction of advanced glycation end products with their counter receptors, contributing to the pathogenesis of vascular complications. We determined whether the interaction of diabetic RBC with HUVEC induced cellular oxidant stress that would culminate in adherence and diapedesis of monocytes, these being initiating events in endothelial injury and atherogenesis. We show that the adherence of diabetic RBC (2% hematocrit), but not normal RBC, to HUVEC results in a fourfold increase in the production of lipid peroxides. Furthermore, diabetic RBC-induced oxidant stress causes a sixfold increase in platelet endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation and doubles transendothelial migration of monocyte-like HL-60 cells; both are blocked by antioxidants and protein kinase C (PKC) inhibitors. Our results show that the adherence of diabetic RBC to endothelial cells initiates a cascade of cellular events resulting in PKC activation, causing PECAM-1 phosphorylation and concomitant transendothelial migration of monocytes. The increased diapedesis of monocytes, brought about by the interaction of diabetic RBC across vascular endothelium, may play an important role in accelerated atherosclerosis and cardiovascular disease in diabetics.
Regional differences in adipose tissue metabolism between sedentary and endurance-trained women.
Authors: Mauriège P , Prud'Homme D , Marcotte M , Yoshioka M , Tremblay A , Després J P
Published: December 2017

Subcutaneous (subc) abdominal and femoral adipose tissue metabolism was studied in sedentary and endurance-trained premenopausal women. Both fat cell weight and lipoprotein lipase (LPL) activity were lower in the subc abdominal depot of trained women compared with controls. Epinephrine- and isoproterenol-stimulated lipolytic responses, as well as the beta-adrenergic sensitivity of subc abdominal adipocytes, were higher in trained than in sedentary women, whereas both the antilipolytic effect of brimonidine (UK-14304) and the alpha 2-adrenoceptor sensitivity were lower in endurance-trained than in sedentary subjects. Maximal lipolysis in the presence of postadrenoceptor agents was also enhanced in subc abdominal adipose cells of trained women compared with sedentary controls. Negative relationships were found between maximal lipolytic responses of subc abdominal fat cells to catecholamines or to postreceptor agents and body fatness as well as abdominal fat distribution indexes. It is concluded that 1) endurance-trained women are characterized by a preferential lipid mobilization from the subc abdominal fat depot, and 2) differences in the metabolic characteristics of subc abdominal adipocytes between trained and sedentary women may involve changes in both LPL activity and the lipolytic cascade that include modifications at receptor and postreceptor levels. However, these alterations appear to be largely resulting from the reduced adipose cell size rather than from exercise training per se.
Potassium currents in ventricular myocytes from genetically diabetic rats
Authors: Tsuchida Katsuharu , Watajima Hiroshi
Published: December 2017

Our previous study demonstrated the longer duration of action potential in ventricular myocytes from genetically diabetic WBN/Kob rats without change in calcium channel density compared with age-matched controls [Tsuchida, K., H. Watajima, and S. Otamo. Am. J. Physiol. 267 ( Heart Circ. Physiol. 36): H2280–H2289, 1994]. In the present study we examined the alteration of potassium currents, especially transient outward current, in ventricular myocytes of genetically diabetic WBN/Kob rats. WBN/Kob rats gradually develop hyperglycemia with aging and show some similarity to non-insulin-dependent diabetes mellitus models, which differ from the insulin-dependent streptozotocin-treated rat model. The density of the intracellular calcium ion-independent transient outward current ( I to) from 17- to 19-mo diabetic rat myocytes was significantly smaller than that from age-matched control rat myocytes. In addition, the density of I to from 17- to 19-mo rat myocytes was significantly less than that from 2-mo rat myocytes, suggesting that aging-induced alteration of I to was accelerated by the diabetic state. The steady-state inactivation curves of I to, the recovery from I toinactivation, and the other outward currents were not significantly altered between diabetic myocytes and age-matched control myocytes. In conclusion, the prolonged duration of action potential from genetically diabetic rat myocytes is mainly due to the depressed I to.
Caloric restriction increases HDL2levels in rhesus monkeys (Macaca mulatta)
Authors: Verdery Roy B. , Ingram Donald K. , Roth George S. , Lane Mark A.
Published: December 2017

Caloric restriction (CR) prolongs the life of rodents and other small animals, but the benefits of CR for primates and people are as yet unknown, and mechanisms by which CR may slow aging remain unidentified. A study of rhesus monkeys, Macaca mulatta, is underway to determine if CR might prolong life span in primates and to evaluate potential mechanisms for life prolongation. Thirty rhesus monkeys in three age cohorts, restricted to 70% of ad libitum calorie intake for 6–7 yr, were compared with 30 controls. Plasma lipid, lipoprotein, and high-density lipoprotein (HDL) apolipoproteins and subfractions were measured and compared with weight, percent fat, glucose, and insulin level. CR caused decreased triglyceride levels in adult monkeys and increased levels of HDL2b, the HDL subfraction associated with protection from atherosclerosis. Multivariate statistical analyses showed that differences in lipid and lipoprotein levels occurring with CR could be accounted for, at least in part, by decreased body mass and improved glucose regulation. These studies have used a novel dietary modification paradigm in nonhuman primates focused on calorie reduction. Results suggest that CR, as mediated by its beneficial effect on body composition and glucose metabolism, could prolong human life by decreasing the incidence of atherosclerosis.
Effects of estrogen and growth hormone on skeleton in the ovariectomized rat with hypophysectomy
Authors: Yeh James K. , Chen Meng-Meng , Aloia John F.
Published: December 2017

To investigate whether growth hormone (GH) and 17β-estradiol (E2) replacement can prevent osteopenia induced by pituitary and ovarian hormone deficiency [by hypophysectomy and ovariectomy (HX+OV)], we administered relatively low doses of GH (2.3 IU ⋅ kg−1 ⋅ day−1) and E2 (100 μg ⋅ kg−1 ⋅ wk−1) in experiment 1 and relatively high doses of GH (13.5 IU ⋅ kg−1 ⋅ day−1) and E2 (3,500 μg ⋅ kg−1 ⋅ wk−1) in experiment 2 to 2-mo-old HX+OV Sprague-Dawley rats for 6 wk. Our data show that the HX+OV of rats results in diminished periosteal bone formation, longitudinal bone growth, and decreased cancellous bone volume. Administration of either the low or high dose of GH to these rats increased their systemic growth, serum levels of osteocalcin, and cortical bone formation. Either low or high doses of GH or E2 alone only partially prevent cancellous bone loss. However, the combined treatment of GH plus E2 resulted in an additive increase in the cancellous bone mass. We conclude that the additive effect of GH plus E2 on cancellous bone is attributed to the suppressive effect of E2 on bone resorption and the anabolic effect of GH on bone formation.
Induction of NO and prostaglandin E2in osteoblasts by wall-shear stress but not mechanical strain
Authors: Smalt R. , Mitchell F. T. , Howard R. L. , Chambers T. J.
Published: December 2017

The nature of the stimulus sensed by bone cells during mechanical usage has not yet been determined. Because nitric oxide (NO) and prostaglandin (PG) production appear to be essential early responses to mechanical stimulation in vivo, we used their production to compare the responsiveness of bone cells to strain and fluid flow in vitro. Cells were incubated on polystyrene film and subjected to unidirectional linear strains in the range 500–5,000 microstrain (με). We found no increase in NO or PGE2production after loading of rat calvarial or long bone cells, MC3T3-E1, UMR-106–01, or ROS 17/2.8 cells. In contrast, exposure of osteoblastic cells to increased fluid flow induced both PGE2and NO production. Production was rapidly induced by wall-shear stresses of 148 dyn/cm2and was observed in all the osteoblastic populations used but not in rat skin fibroblasts. Fluid flow appeared to act through an increase in wall-shear stress. These data suggest that mechanical loading of bone is sensed by osteoblastic cells through fluid flow-mediated wall-shear stress rather than by mechanical strain.
Reduced insulin receptor signaling in the obese spontaneously hypertensive Koletsky rat
Authors: Friedman Jacob E. , Ishizuka Tatsuya , Liu Sha , Farrell Craig J. , Bedol David , Koletsky Richard J. , Kaung Hue-Lee , Ernsberger Paul
Published: December 2017

Insulin resistance is associated with both obesity and hypertension. However, the cellular mechanisms of insulin resistance in genetic models of obese-hypertension have not been identified. The objective of the present study was to investigate the effects of genetic obesity on a background of inherited hypertension on initial components of the insulin signal transduction pathway and glucose transport in skeletal muscle and liver. Oral glucose tolerance testing in SHROB demonstrated a sustained postchallenge elevation in plasma glucose at 180 and 240 min compared with lean spontaneously hypertensive rat (SHR) littermates, which is suggestive of glucose intolerance. Fasting plasma insulin levels were elevated 18-fold in SHROB. The rate of insulin-stimulated 3- O-methylglucose transport was reduced 68% in isolated epitrochlearis muscles from the SHROB compared with SHR. Insulin-stimulated tyrosine phosphorylation of the insulin receptor β-subunit and insulin receptor substrate-1 (IRS-1) in intact skeletal muscle of SHROB was reduced by 36 and 23%, respectively, compared with SHR, due primarily to 32 and 60% decreases in insulin receptor and IRS-1 protein expression, respectively. The amounts of p85α regulatory subunit of phosphatidylinositol-3-kinase and GLUT-4 protein were reduced by 28 and 25% in SHROB muscle compared with SHR. In the liver of SHROB, the effect of insulin on tyrosine phosphorylation of IRS-1 was not changed, but insulin receptor phosphorylation was decreased by 41%, compared with SHR, due to a 30% reduction in insulin receptor levels. Our observations suggest that the leptin receptor mutation fakimposed on a hypertensive background results in extreme hyperinsulinemia, glucose intolerance, and decreased expression of postreceptor insulin signaling proteins in skeletal muscle. Despite these changes, hypertension is not exacerbated in SHROB compared with SHR, suggesting these metabolic abnormalities may not contribute to hypertension in this model of Syndrome X.
Reversal of chronic alterations of skeletal muscle protein kinase C from fat-fed rats by BRL-49653
Authors: Schmitz-Peiffer Carsten , Oakes Nicholas D. , Browne Carol L. , Kraegen Edward W. , Biden Trevor J.
Published: December 2017

We have recently shown that the reduction in insulin sensitivity of rats fed a high-fat diet is associated with the translocation of the novel protein kinase Cε(nPKCε) from cytosolic to particulate fractions in red skeletal muscle and also the downregulation of cytosolic nPKCθ. Here we have further investigated the link between insulin resistance and PKC by assessing the effects of the thiazolidinedione insulin-sensitizer BRL-49653 on PKC isoenzymes in muscle. BRL-49653 increased the recovery of nPKC isoenzymes in cytosolic fractions of red muscle from fat-fed rats, reducing their apparent activation and/or downregulation, whereas PKC in control rats was unaffected. Because BRL-49653 also improves insulin-stimulated glucose uptake in fat-fed rats and reduces muscle lipid storage, especially diglyceride content, these results strengthen the association between lipid availability, nPKC activation, and skeletal muscle insulin resistance and support the hypothesis that chronic activation of nPKC isoenzymes is involved in the generation of muscle insulin resistance in fat-fed rats.
Leucine metabolism in TNF-α- and endotoxin-treated rats: contribution of hepatic tissue
Authors: Holeček M. , Šprongl L. , Skopec F. , Andrýs C. , Pecka M.
Published: December 2017

The effects of tumor necrosis factor-α (TNF-α; cachectin) and lipopolysaccharide of Salmonella enteritidis (LPS; endotoxin) on leucine metabolism in rats were evaluated in the whole body using intravenous infusion ofl-[1-14C]leucine and in isolated perfused liver (IPL) using the single-pass perfusion technique with α-keto[1-14C]isocaproate as a tracer for measurement of ketoisocaproic acid (KIC) oxidation, and the recirculation technique for measurement of hepatic amino acid exchanges. The data obtained in TNF-α and LPS groups were compared with those obtained in controls. Both TNF-α and LPS treatment induced an increase of whole body leucine turnover, oxidation, and clearance. As the result of a higher increase of leucine oxidation than of incorporation into the pool of body proteins, the fractional oxidation of leucine was increased. The fractional rate of protein synthesis increased significantly in the spleen (both in TNF-α and LPS rats), in blood plasma, liver, colon, kidneys, gastrocnemius muscle (in LPS rats), and in lungs (TNF-α-treated rats), whereas it decreased in the jejunum (LPS rats). In IPL of TNF-α- and LPS-treated rats a decrease of KIC oxidation and higher uptake of branched-chain amino acids (BCAA; valine, leucine, and isoleucine) were observed when compared with control animals. We hypothesize that the negative consequences of increased whole body proteolysis and of increased oxidation of BCAA induced by TNF-α and/or LPS are reduced by decreased activity of hepatic branched-chain ketoacid dehydrogenase that can help resupply BCAA to the body.
Skeletal unloading inhibits the in vitro proliferation and differentiation of rat osteoprogenitor cells
Authors: Kostenuik Paul J. , Halloran Bernard P. , Morey-Holton Emily R. , Bikle Daniel D.
Published: December 2017

Loss of weight bearing in the growing rat decreases bone formation, osteoblast numbers, and bone maturation in unloaded bones. These responses suggest an impairment of osteoblast proliferation and differentiation. To test this assumption, we assessed the effects of skeletal unloading using an in vitro model of osteoprogenitor cell differentiation. Rats were hindlimb elevated for 0 (control), 2, or 5 days, after which their tibial bone marrow stromal cells (BMSCs) were harvested and cultured. Five days of hindlimb elevation led to significant decreases in proliferation, alkaline phosphatase (AP) enzyme activity, and mineralization of BMSC cultures. Differentiation of BMSCs was analyzed by quantitative competitive polymerase chain reaction of cDNA after 10, 15, 20, and 28 days of culture. cDNA pools were analyzed for the expression of c- fos (an index of proliferation), AP (an index of early osteoblast differentiation), and osteocalcin (a marker of late differentiation). BMSCs from 5-day unloaded rats expressed 50% less c- fos, 61% more AP, and 35% less osteocalcin mRNA compared with controls. These data demonstrate that cultured osteoprogenitor cells retain a memory of their in vivo loading history and indicate that skeletal unloading inhibits proliferation and differentiation of osteoprogenitor cells in vitro.
Galanin is localized in sympathetic neurons of the dog liver
Authors: Mundinger Thomas O. , Verchere C. Bruce , Baskin Denis G. , Boyle Michael R. , Kowalyk Stephan , Taborsky Gerald J.
Published: December 2017

Stimulation of canine hepatic nerves releases the neuropeptide galanin from the liver; therefore, galanin may be a sympathetic neurotransmitter in the dog liver. To test this hypothesis, we used immunocytochemistry to determine if galanin is localized in hepatic sympathetic nerves and we used hepatic sympathetic denervation to verify such localization. Liver sections from dogs were immunostained for both galanin and the sympathetic enzyme marker tyrosine hydroxylase (TH). Galanin-like immunoreactivity (GALIR) was colocalized with TH in many axons of nerve trunks as well as individual nerve fibers located both in the stroma of hepatic blood vessels and in the liver parenchyma. Neither galanin- nor TH-positive cell bodies were observed. Intraportal 6-hydroxydopamine (6-OHDA) infusion, a treatment that selectively destroys hepatic adrenergic nerve terminals, abolished the GALIR staining in parenchymal neurons but only moderately diminished the GALIR staining in the nerve fibers around blood vessels. To confirm that 6-OHDA pretreatment proportionally depleted galanin and norepinephrine in the liver, we measured both the liver content and the hepatic nerve-stimulated spillover of galanin and norepinephrine from the liver. Pretreatment with 6-OHDA reduced the content and spillover of both galanin and norepinephrine by >90%. Together, these results indicate that galanin in dog liver is primarily colocalized with norepinephrine in sympathetic nerves and may therefore function as a hepatic sympathetic neurotransmitter.
Responses to angiotensin peptides are mediated by AT1 receptors in the rat
Authors: Champion Hunter C. , Czapla Marc A. , Kadowitz Philip J.
Published: December 2017

The effects of the angiotensin AT1 and AT2 receptor antagonists candesartan and PD-123,319 on hemodynamic responses to angiotensin peptides were investigated in the anesthetized rat. Injections of angiotensin II and III caused dose-related increases in systemic arterial and in hindquarters perfusion pressure that were reduced in an insurmountable manner by candesartan. Pressor responses to angiotensin IV were also attenuated, and a vasodepressor or vasodilator response to the angiotensin peptides was not unmasked by the AT1 receptor antagonists candesartan or losartan. The AT2receptor antagonist PD-123,319 had no significant effect on increases in systemic arterial and hindquarters perfusion pressure in response to the angiotensin peptides. Pressor responses to angiotensin peptides were not altered by adrenergic nerve terminal and α-receptor blocking agents or by the cyclooxygenase inhibitor sodium meclofenamate but were increased by an inhibitor of nitric oxide synthase. The present results suggest that pressor responses to the angiotensin peptides are mediated by the activation of AT1 receptors and that AT2 receptors, the adrenergic system, or cyclooxygenase products do not appear to modulate hemodynamic responses to the angiotensin peptides in the anesthetized rat.
Regulation of hexokinase II activity and expression in human muscle by moderate exercise
Authors: Koval Janice A. , DeFronzo Ralph A. , O’Doherty Robert M. , Printz Richard , Ardehali Hossein , Granner Daryl K. , Mandarino Lawrence J.
Published: December 2017

A single bout of exercise increases the rate of insulin-stimulated glucose uptake and metabolism in skeletal muscle. Exercise also increases insulin-stimulated glucose 6-phosphate in skeletal muscle, suggesting that exercise increases hexokinase activity. Within 3 h, exercise increases hexokinase II (HK II) mRNA and activity in skeletal muscle from rats. It is not known, however, if a single bout of moderate-intensity exercise increases HK II expression in humans. The present study was undertaken to answer this question. Six subjects had percutaneous biopsies of the vastus lateralis muscle before and 3 h after a single 3-h session of moderate-intensity aerobic (60% of maximal oxygen consumption) exercise. Glycogen synthase, HK I, and HK II activities as well as HK I and HK II mRNA content were determined from the muscle biopsy specimens. The fractional velocity of glycogen synthase was increased by 446 ± 84% after exercise ( P < 0.005). Hexokinase II activity in the soluble fraction of the homogenates increased from 1.2 ± 0.4 to 4.5 ± 1.6 pmol ⋅ min−1⋅ μg−1( P < 0.05) but was unchanged in the particulate fraction (4.3 ± 1.3 vs. 5.3 ± 1.5). HK I activity in neither the soluble nor particulate fraction changed after exercise. Relative to a 28S rRNA control signal, HK II mRNA increased from 0.091 ± 0.02 to 0.195 ± 0.037 ( P < 0.05), whereas HK I mRNA was unchanged (0.414 ± 0.061 vs. 0.498 ± 0.134, P < 0.20). The increase in HK II activity after moderate exercise in healthy subjects could be one factor responsible for the enhanced rate of insulin-stimulated glucose uptake seen after exercise.
Insulin sensitivity is associated with blood pressure response to sodium in older hypertensives
Authors: Dengel Donald R. , Hogikyan Robert V. , Brown Michael D. , Glickman Scott G. , Supiano Mark A.
Published: December 2017

The purpose of this study was to determine whether sodium-resistant hypertensives are more insulin resistant and whether dietary sodium restriction improves insulin sensitivity in older hypertensives. Insulin sensitivity was assessed by a frequently sampled intravenous glucose tolerance test to determine the insulin sensitivity index (SI) after 1 wk each of low- (20 mmol ⋅ l−1 ⋅ day−1) and high- (200 mmol ⋅ l−1 ⋅ day−1) sodium diets in 21 older (63 ± 2 yr) hypertensives. Subjects were grouped on the difference in mean arterial blood pressure (MABP) between diets [sodium sensitive (SS): ≥5-mmHg increase in MABP on the high-sodium diet ( n = 14); sodium resistant (SR): <5-mmHg increase in MABP on the high-sodium diet ( n = 7)]. There was no dietary sodium effect on fasting plasma insulin or SI. An analysis of variance indicated a significant ( P = 0.0002) group effect, with SS individuals having lower fasting plasma insulins on the low- (13 ± 2 vs. 27 ± 3 μU/ml) and high- (12 ± 2 vs. 22 ± 3 μU/ml) sodium diets compared with SR individuals. Similarly, there was a significant ( P= 0.0002) group effect in regard to SI, with SS individuals having significantly higher SI on the low- (3.26 ± 0.60 vs. 0.91 ± 0.31 μU × 10−4 ⋅ min−1 ⋅ ml−1) and high- (3.45 ± 0.51 vs. 1.01 ± 0.30 μU × 10−4 ⋅ min−1 ⋅ ml−1) sodium diets compared with SR individuals. We conclude that SR individuals exhibit a greater degree of insulin resistance than SS individuals and that dietary sodium restriction fails to improve insulin sensitivity regardless of sodium sensitivity status.
Regulation of fatty acid oxidation in untrained vs. trained men during exercise
Authors: Sidossis Labros S. , Wolfe Robert R. , Coggan Andrew R.
Published: December 2017

We have recently shown that increased carbohydrate flux decreases fat oxidation during exercise by inhibition of fatty acid entry into the mitochondria. Because endurance training reduces the rate of carbohydrate flux during exercise, we hypothesized that training increases fat oxidation by relieving this inhibition. To test this hypothesis, five sedentary and five endurance-trained men exercised on a cycle ergometer at an oxygen consumption (V˙o2) of ∼2.0 l/min, representing 80 and 40% peakV˙o2, respectively. [1-13C]oleate and [1-14C]octanoate, long- and medium-chain fatty acids, respectively, were infused for the duration of the studies. Carbohydrate oxidation was significantly higher in the sedentary group (196 ± 9 vs. 102 ± 17 μmol ⋅ kg−1⋅ min−1, P < 0.05). Oleate oxidation was higher in the trained group (3.8 ± 0.6 vs. 1.9 ± 0.3 μmol ⋅ kg−1⋅ min−1, P < 0.05), whereas octanoate oxidation was not different between the two groups. The percentage of oleate that was taken up by tissues and oxidized was higher in the trained group (76 ± 7 vs. 58 ± 3%, P < 0.05). However, the percentage of octanoate taken up and oxidized was not different (82 ± 3 vs. 85 ± 4%, not significant). Because octanoate, unlike oleate, can freely diffuse across the mitochondrial membrane, the present results suggest that the difference in fatty acid oxidation between trained and untrained individuals may be due to enhanced fatty acid entry into the mitochondria.
Tracer methods underestimate short-term variations in urea production in humans
Authors: Hamadeh Mazen J. , Hoffer L. John
Published: December 2017

Urea production rate (Ra) is commonly measured using a primed continuous tracer urea infusion, but the accuracy of this method has not been clearly established in humans. We used intravenous infusions of unlabeled urea to assess the accuracy of this technique in normal, postabsorptive men under the following four different conditions: 1) tracer [13C]urea was infused under basal conditions for 12 h (control); 2) tracer [13C]urea was infused for 12 h, and unlabeled urea was infused from hours 4 to 12 at a rate twofold greater than the endogenous Ra (“step” infusion); 3) tracer [13C]urea was infused for 12 h, and unlabeled urea was infused from hours 4 to 8 (“pulse” infusion); and 4) tracer [13C]urea was infused for 9 h, and unlabeled alanine was infused at a rate of 120 mg ⋅ kg−1 ⋅ h−1(1.35 mmol ⋅ kg−1 ⋅ h−1) from hours 4 to 9. Urea Ra was calculated using the isotopic steady-state equation (tracer infusion rate/tracer-to-tracee ratio), Steele’s non-steady-state equation, and urinary urea excretion corrected for changes in total body urea. For each subject, endogenous urea Ra was measured at hour 4 of the basal condition, and the sum of this rate plus exogenous urea input was considered as “true urea input.” Under control conditions, urea Ra at hour 4 was similar to that measured at hour 12. After 8-h step and 4-h pulse unlabeled urea infusions, Steele’s non-steady-state equation underestimated true urea input by 22% (step) and 33% (pulse), whereas the nonisotopic method underestimated true urea input by 28% (step) and 10% (pulse). Similar conclusions were derived from the alanine infusion. These results indicate that, although Steele’s non-steady-state equation and the nontracer method more accurately predict total urea Ra than the steady-state equation, they nevertheless seriously underestimate total urea Ra for as long as 8 h after a change in true urea Ra.
Phosphatidylinositol 3-kinase activation is required for insulin-stimulated sodium transport in A6 cells
Authors: Record Rae D. , Froelich Larry L. , Vlahos Chris J. , Blazer-Yost Bonnie L.
Published: December 2017

Insulin stimulates amiloride-sensitive sodium transport in models of the distal nephron. Here we demonstrate that, in the A6 cell line, this action is mediated by the insulin receptor tyrosine kinase and that activation of phosphatidylinositol 3-kinase (PI 3-kinase) lies downstream of the receptor tyrosine kinase. Functionally, a specific inhibitor of PI 3-kinase, LY-294002, blocks basal as well as insulin-stimulated sodium transport in a dose-dependent manner (IC50≈ 6 μM). Biochemically, PI 3-kinase is present in A6 cells and is inhibited both in vivo and in vitro by LY-294002. Furthermore, a subsequent potential downstream signaling element, pp70 S6 kinase, is activated in response to insulin but does not appear to be part of the pathway involved in insulin-stimulated sodium transport. Together with previous reports, these results suggest that insulin may induce the exocytotic insertion of sodium channels into the apical membrane of A6 cells in a PI 3-kinase-mediated manner.
Population-based modeling to demonstrate extrapancreatic effects of tolbutamide
Authors: Rostami-Hodjegan A. , Peacey S. R. , George E. , Heller S. R. , Tucker G. T.
Published: December 2017

Tolbutamide is used increasingly as an investigative tool in in vivo studies of the physiology of glucose tolerance. Its hypoglycemic effect in nondiabetic subjects is widely variable, reflecting possible variability in its pharmacokinetics, an insulinergic response, an extrapancreatic effect of the drug, or the hypoglycemic effect of insulin itself. Using population-based modeling, we have investigated the kinetics and dynamics of tolbutamide and assessed covariates in two groups of healthy subjects. The results indicate a high variability in insulinergic effect, measured by the area under of the curve of insulin (0–60 min), in response to tolbutamide injection (coefficient of variation = 29–96%). However, it appears that impaired insulin sensitivity is compensated by higher insulin secretion in response to tolbutamide. Thus the hypoglycemic effect of high insulin secretion is minimal in insulin-resistant subjects. Application of the model indicated that tolbutamide has appreciable extrapancreatic effects mediated by prolongation of the residence time of insulin in a remote effect and by enhancement of glucose effectiveness. An effect in increasing the insulin sensitivity index is also possible but could not be confirmed statistically for all groups of subjects studied. These observations may explain inconsistencies between the results of tolbutamide and insulin injection in the frequently sampled intravenous glucose tolerance test and call for further study of insulin- vs. tolbutamide-modified frequently sampled intravenous glucose tolerance tests in the assessment of the insulin sensitivity and glucose effectiveness indexes.
Mass isotopomer study of the nonoxidative pathways of the pentose cycle with [1,2-13C2]glucose
Authors: Lee Wai-Nang Paul , Boros Laszlo G. , Puigjaner Joaquim , Bassilian Sara , Lim Shu , Cascante Marta
Published: December 2017

We present a single-tracer method for the study of the pentose phosphate pathway (PPP) using [1,2-13C2]glucose and mass isotopomer analysis. The metabolism of [1,2-13C2]glucose by the glucose-6-phosphate dehydrogenase, transketolase (TK), and transaldolase (TA) reactions results in unique pentose and lactate isotopomers with either one or two13C substitutions. The distribution of these isotopomers was used to estimate parameters of the PPP using the model of Katz and Rognstad (J. Katz and R. Rognstad. Biochemistry 6: 2227–2247, 1967). Mass and position isotopomers of ribose, and lactate and palmitate (products from triose phosphate) from human hepatoma cells (Hep G2) incubated with 30% enriched [1,2-13C2]glucose were determined using gas chromatography-mass spectrometry. After 24–72 h incubation, 1.9% of lactate molecules in the medium contained one13C substitution ( m1) and 10% contained two13C substitutions ( m2). A similar m1-to- m2ratio was found in palmitate as expected. Pentose cycle (PC) activity determined from incubation with [1,2-13C2]glucose was 5.73 ± 0.52% of the glucose flux, which was identical to the value of PC (5.55 ± 0.73%) determined by separate incubations with [1-13C] and [6-13C]glucose.13C was found to be distributed in four ribose isotopomers ([1-13C]-, [5-13C]-, [1,2-13C2]-, and [4,5-13C2]ribose). The observed ribose isotopomer distribution was best matched with that provided from simulation by substituting 0.032 for TK and 0.85 for TA activity relative to glucose uptake into the model of Katz and Rognstad. The use of [1,2-13C2]glucose not only permits the determination of PC but also allows estimation of relative rates through the TK and TA reactions.
Vagotomy in young obese hyperglycemic mice: effects on syndrome development and islet proliferation
Authors: Edvell Anders , Lindström Per
Published: December 2017

Obese hyperglycemic mice have large pancreatic islets and high levels of serum insulin and blood glucose. Vagotomy was performed on 3-wk-old animals to investigate the role of gut cholinergic innervation in young Umeå ob/ob mice. After vagotomy, obesity and hyperglycemia are dissociated. Weight increase in obese vagotomized mice was lower than in sham-operated controls during the 1st wk postoperatively but not thereafter. Blood glucose was lower up to 5 mo after vagotomy, but vagotomized mice showed reduced glucose tolerance. Islet cell proliferation rate was reduced 2 and 3 wk but not 5 mo after vagotomy. After 5 mo, islet volume was smaller in vagotomized mice. Serum insulin levels were the same in vagotomized animals as in sham-operated controls. The effects of reduced cholinergic innervation are probably caused both by direct effects of denervation and by lowered metabolic demand.
Acute-phase protein response to infection in severe malnutrition
Authors: Morlese John F. , Forrester Terrence , Jahoor Farook
Published: December 2017

It is not known whether malnourished infants can mount a comprehensive acute-phase protein (APP) response and, if so, whether this is achieved by increasing APP synthesis rates. To address these issues, we measured 1) the plasma concentrations of five APPs (C-reactive protein, α1-acid glycoprotein, α1-antitrypsin, haptoglobin, and fibrinogen) and 2) the synthesis rates of three APPs (α1-antitrypsin, haptoglobin, and fibrinogen) using a constant intragastric infusion of [2H3]leucine in nine infected marasmic children at ∼2 days postadmission ( study 1), ∼9 days postadmission when infections had cleared ( study 2), and ∼59 days postadmission at recovery ( study 3). Except for fibrinogen, the plasma concentrations of all APPs were higher in study 1 than in studies 2 and 3. Although the rate of synthesis of haptoglobin was significantly greater in study 1 than study 2, the rates of fibrinogen and α1-antitrypsin synthesis were similar in all three studies. These results show that 1) severely malnourished children can mount an APP response to infection which does not include fibrinogen and 2) the APP response is accomplished through different mechanisms.
Responses of hepatic TNF-α mRNA to repeated hemorrhage in the conscious rat
Authors: Yamashita Masatomo , Yamashita Mamoru
Published: December 2017

Trauma victims may suffer from repeated hemorrhage, but responses of cytokines to it have not been described. To study this question, we first detected the time course of changes in serum tumor necrosis factor (TNF) activity and hepatic TNF-α mRNA by cytotoxicity against L929 cells and by reverse transcription (RT) and polymerase chain reaction (PCR), respectively, after different sizes of hemorrhage (10–20 ml/kg) with chronically cannulated rats. Then we examined the changes in TNF-α mRNA when two sequential 10 ml/kg hemorrhages were performed. TNF activity showed no significant increases after either size of hemorrhage. At mRNA level, both 15 ml/kg and 20 ml/kg hemorrhages induced significant increases after hemorrhage, whereas a 10 ml/kg hemorrhage did not. When the 10 ml/kg hemorrhage was repeated 24 h later, however, TNF-α mRNA showed a significant increase. There were no significant differences in blood pressure and heart rate after single and repeated 10 ml/kg hemorrhage. This potentiation persisted for ≥48 h. These results show that responses of hepatic TNF-α mRNA are augmented when moderate hemorrhage is repeated.
Infused IGF-I/IGFBP-3 complex causes glomerular localization of IGF-I in the rat kidney
Authors: Sandra Alexander , Boes Mary , Dake Brian L. , Stokes John B. , Bar Robert S.
Published: December 2017

Insulin-like growth factor I (IGF-I) increases renal blood flow, glomerular filtration rate (GFR), and proximal tubule reabsorption of phosphate in humans and rodents. The biological effects of IGF-I are likely to be influenced by cellular localization of IGF-I within the kidney. We therefore tested whether the renal localization of infused IGF-I could be altered if given with selected IGF-binding proteins (IGFBPs). Rats were treated with intravenous injections of125I-labeled IGF-I,125I-IGFBP-3, or125I-IGFBP-4 alone or with complexes of125I-IGF-I and IGFBP-3 or IGFBP-4. The cellular localization of IGF and the IGFBP within the kidney was then determined.125I-IGF-I,125I-IGFBP-4, and125I-IGF-I/IGFBP-4 complexes were found almost exclusively in vacuolar structures (endosomes) of proximal renal tubules. In contrast, about one-third of renal125I-IGFBP-3 and125I-IGF-I/IGFBP-3 was localized to glomeruli. When125I-IGF-I was given alone, 3% was found in glomeruli and 89% in proximal tubules. When given as125I-IGF-I/IGFBP-3, 29% was in glomeruli and 65% in proximal tubules. We conclude that the cellular localization of IGF-I within the kidney can be directed to glomerular elements if the IGF-I is given with IGFBP-3.
In vivo regulation of acyl-CoA synthetase mRNA and activity by endotoxin and cytokines
Authors: Memon Riaz A. , Fuller John , Moser Arthur H. , Smith Pamela J. , Feingold Kenneth R. , Grunfeld Carl
Published: December 2017

Acyl-CoA synthetase (ACS) catalyzes the activation of fatty acids (FA) to acyl-CoA esters, which are further metabolized in either anabolic or catabolic pathways. Endotoxin [lipopolysaccharide (LPS)], tumor necrosis factor (TNF), and interleukin-1 (IL-1) enhance hepatic FA synthesis and reesterification and inhibit FA oxidation. LPS also decreases triglyceride storage in adipose tissue and inhibits the uptake of FA by heart and muscle. Therefore, in this study we examined the effects of LPS and cytokines on ACS (now also known as ACS1) mRNA expression and activity in multiple tissues in Syrian hamsters. LPS markedly decreased ACS1 mRNA levels in liver, adipose tissue, heart, and skeletal muscle. The inhibitory effects of LPS on ACS1 mRNA levels in liver and adipose tissue were observed as early as 2–4 h after administration, became maximal by 4–8 h, and were sustained for ≥24 h. Very low doses of LPS (0.1–1 μg/100 g body wt) were needed to reduce ACS1 mRNA levels in liver and adipose tissue. TNF and IL-1 mimicked the effect of LPS on ACS1 mRNA levels in liver and adipose tissue. LPS decreased ACS activity in adipose tissue, heart, and muscle. In liver, where ACS is localized in several subcellular organelles, both LPS and cytokines decreased mitochondrial ACS activity, whereas they increased microsomal ACS activity. Taken together, these results indicate that LPS and cytokines decrease ACS1 mRNA expression and ACS activity in tissues where FA uptake and/or oxidation is decreased during sepsis. In liver, where FA oxidation is decreased during sepsis but the reesterification of FA is increased, LPS and cytokines decrease ACS1 mRNA and mitochondrial ACS activity, which may inhibit FA oxidation, but increase microsomal ACS activity, which may support the reesterification of peripherally derived FA for triglyceride synthesis.
Effects of growth hormone on steroid-induced increase in ability of urea synthesis and urea enzyme mRNA levels
Authors: Grøfte Thorbjørn , Jensen Dorthe Svenstrup , Grønbæk Henning , Wolthers Troels , Jensen Søren Astrup , Tygstrup Niels , Vilstrup Hendrik
Published: December 2017

Growth hormone (GH) reduces the catabolic side effects of steroid treatment due to its effects on tissue protein synthesis/degradation. Little attention is focused on hepatic amino acid degradation and urea synthesis. Five groups of rats were given 1) placebo, 2) prednisolone, 3) placebo, pair fed to the steroid group, 4) GH, and 5) prednisolone and GH. After 7 days, the in vivo capacity of urea N synthesis (CUNS) was determined by saturating alanine infusion, in parallel with measurements of liver mRNA levels of urea cycle enzymes, N contents of organs, N balance, and hormones. Prednisolone increased CUNS (μmol ⋅ min−1⋅ 100 g−1, mean ± SE) from 9.1 ± 1.0 (pair-fed controls) to 13.2 ± 0.8 ( P < 0.05), decreased basal blood α-amino N concentration from 4.2 ± 0.5 to 3.1 ± 0.3 mmol/l ( P < 0.05), increased mRNA levels of the rate- and flux-limiting urea cycle enzymes by 20 and 65%, respectively ( P < 0.05), and decreased muscle N contents and N balance. In contrast, GH decreased CUNS from 6.1 ± 0.9 (free-fed controls) to 4.2 ± 0.5 ( P < 0.05), decreased basal blood α-amino N concentration from 3.8 ± 0.3 to 3.2 ± 0.2, decreased mRNA levels of the rate- and flux-limiting urea cycle enzymes to 60 and 40%, respectively ( P < 0.05), and increased organ N contents and N balance. Coadministration of GH abolished all steroid effects. We found that prednisolone increases the ability of amino N conversion into urea N and urea cycle gene expression. GH had the opposite effects and counteracted the N-wasting side effects of prednisolone.
Stimulatory effect of lithium on glucose transport in rat adipocytes is not mediated by elevation of IP1
Authors: Chen Xiaoli , McMahon Ellen G. , Gulve Eric A.
Published: December 2017

Lithium has been shown to increase glucose uptake in skeletal muscle and adipose tissues. The therapeutic effect of lithium on bipolar disease is thought to be mediated by its inhibitory effect on myo-inositol-1-monophosphatase (IMPase). We tested the hypothesis that the stimulatory effect of lithium on glucose uptake results from inhibition of IMPase and the resultant accumulation of inositol monophosphates (IP1) by comparing the effects of lithium and a selective IMPase inhibitor, L-690,488, on isolated rat adipocytes. Insulin produced a concentration-dependent stimulation of 2-deoxy-d-[14C]glucose (2-DG) transport (10 μU/ml caused half-maximal activation). Acute exposure to lithium stimulated basal glucose transport activity in a concentration-dependent manner, with a threefold stimulation at 30 mM lithium. Lithium also potentiated insulin-stimulated 2-DG transport. Lithium produced a concomitant increase in IP1accumulation. In contrast, L-690,488 increased IP1to levels comparable to those of lithium without stimulatory effects on 2-DG transport. These results demonstrate that stimulatory effects of lithium on glucose transport are not mediated by the inhibition of IMPase and subsequent accumulation of IP1in rat adipocytes.
The 24-h whole body leucine and urea kinetics at normal and high protein intakes with exercise in healthy adults
Authors: Forslund Anders H. , Hambraeus Leif , Olsson Roger M. , El-Khoury Antoine E. , Yu Yong-Ming , Young Vernon R.
Published: December 2017

In healthy adult men adapted to a diet/exercise regimen for 6 days, the effects of small, frequent meals supplying daily protein intakes of 1 ( n = 8) or 2.5 g ⋅ kg−1 ⋅ day−1( n = 6) on leucine oxidation, urea production, and whole body protein synthesis (PS) and degradation (PD) have been compared with the use of a 24-h continuous intravenous [13C]leucine and [15N,15N]urea infusion protocol. Two 90-min periods of exercise (∼50% maximal O2 consumption) were included during the fasting and the fed periods of the 24-h day. Subjects were determined to be at approximate energy, nitrogen, and leucine balances on both diets. Increased protein intake raised the urea production rate; the absolute rate of urea hydrolysis was the same on both diets. When the first-pass splanchnic uptake of leucine was taken to be 25% of intake, PS was stimulated by feeding (after an overnight fast) at both protein intake levels ( P < 0.05 and P < 0.01), whereas PD declined significantly ( P < 0.01) at both protein levels. Protein gain at a high protein intake appears to be the result of both a stimulation of PS and a marked decline in PD, whereas at a less generous intake, the gain appears to be a result of a fall in PD with a less evident change in PS. Exercise moderately decreased PS during and/or immediately after exercise at each protein level, and there was a postexercise-induced increase ( P < 0.01) in PD, which was more dramatic when feeding was at the higher protein intake level.
Plasma leptin concentrations are only transiently increased in nephrectomized rats
Authors: Landt Michael , Martin Daniel R. , Zeng Jianbo , Miller Steven B. , Kohrt Wendy M. , Patterson Bruce W.
Published: December 2017

Leptin is an adipocyte-secreted hormone that has effects on appetite and energy expenditure. Several studies have shown that end-stage renal disease results in elevated plasma leptin concentrations and that the kidney is responsible for most of leptin elimination in rodents. Leptin metabolism was investigated in rats that underwent unilateral nephrectomy to experimentally limit renal elimination function. Within 4 h of nephrectomy, plasma leptin concentrations increased from 2.9 ± 0.8 to 5.8 ± 1.0 μg/l but thereafter rapidly (<24 h) decreased to prenephrectomy concentrations, despite continued elevated plasma creatinine levels. Sham-operated rats maintained presurgical concentrations of leptin and creatinine throughout the experiment. Kinetic studies of125I-labeled leptin elimination showed that fractional catabolic rates and half-lives of leptin in circulation were similar at 48 h in nephrectomized and sham-operated rats, suggesting that production of leptin was unchanged after nephrectomy. Excretion of125I derived from leptin in urine of nephrectomized rats was similar to that of sham-operated rats, and residual radioactivity was increased in the remaining kidneys excised from nephrectomized rats. These results demonstrate that 1) leptin concentrations are quickly restored to presurgical levels in nephrectomized rats, and 2) it is leptin elimination, not leptin production, that compensates to maintain leptin concentrations. Rapid metabolic adaptation of remaining renal tissue may explain the restoration of normal leptin elimination in nephrectomized rats.