Effects of FFA on insulin-stimulated glucose fluxes and muscle glycogen synthase activity in rats

1998 ◽  
Vol 275 (2) ◽  
pp. E338-E344 ◽  
Author(s):  
Joong-Yeol Park ◽  
Chul-Hee Kim ◽  
Sung K. Hong ◽  
Kyo I. Suh ◽  
Ki-Up Lee
Keyword(s):  
Skeletal Muscle ◽  
Muscle Glycogen ◽  
Infusion Rate ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Glucose Infusion ◽  
Glucose Infusion Rate ◽  
Whole Body ◽  
Heparin Infusion ◽  
Muscle Glycogen Synthesis

To examine effects of free fatty acids (FFA) on insulin-stimulated glucose fluxes, euglycemic hyperinsulinemic (86 pmol ⋅ kg−1 ⋅ min−1) clamps were performed for 5 h in conscious rats with ( n = 8) or without ( n = 8) lipid-heparin infusion. Glucose infusion rate required to maintain euglycemia was not different between the two groups during the first 2 h of clamps but became significantly lower with lipid-heparin infusion in the 3rd h and thereafter. To investigate changes in intracellular glucose metabolism during lipid-heparin infusion, additional clamps ( n = 8 each) were performed for 1, 2, 3, or 5 h with an infusion of [3-3H]glucose. Insulin-stimulated whole body glucose utilization (Rd), glycolysis, and glycogen synthesis were estimated on the basis of tracer concentrations in plasma during the final 40 min of each clamp. Similar to changes in glucose infusion rate, Rd was not different between the two groups in the 1st and 2nd h but was significantly lower with lipid-heparin infusion in the 3rd h and thereafter. Whole body glycolysis was significantly lower with lipid-heparin infusion in all time periods, i.e., 1st, 2nd, 3rd, and 5th h of clamps. In contrast, whole body glycogen synthesis was higher with lipid-heparin infusion in the 1st and 2nd h but lower in the 5th h. Similarly, accumulation of [3H]glycogen radioactivity in muscle glycogen was significantly higher with lipid-heparin during the 1st and 2nd h but lower during the 3rd and 5th h. Glucose 6-phosphate (G-6- P) concentrations in gastrocnemius muscles were significantly higher with lipid-heparin infusion throughout the clamps. Muscle glycogen synthase (GS) activity was not altered with lipid-heparin infusion at 1, 2, and 3 h but was significantly lower at 5 h. Thus increased availability of FFA significantly reduced whole body glycolysis, but compensatory increase in skeletal muscle glycogen synthesis in association with accumulation of G-6- P masked this effect, and Rd was not affected in the early phase (within 2 h) of lipid-heparin infusion. Rd was reduced in the later phase (>2 h) of lipid-heparin infusion, when glycogen synthesis was reduced in association with reduced skeletal muscle GS activity.

Quantitation of glycolysis and skeletal muscle glycogen synthesis in humans

1993 ◽  
Vol 265 (5) ◽  
pp. E761-E769 ◽  
Author(s):  
L. Rossetti ◽  
Y. T. Lee ◽  
J. Ruiz ◽  
S. C. Aldridge ◽  
H. Shamoon ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Muscle Glycogen ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Whole Body ◽  
Skeletal Muscle Glycogen ◽  
Muscle Glycogen Synthesis ◽  
The Difference ◽  
Total Glucose

We measured the net rates of skeletal muscle glycogen synthesis and glycolysis (conversion of [3-3H]glucose to 3H2O) in healthy overnight-fasted volunteers. Two studies were performed. In study 1, seven subjects participated in two paired infusions under basal conditions of either [2-3H]glucose (H2) or [3-3H]glucose (H3). Total glucose uptake (Rd) and rates of whole body 3H2O formation (3H2O Ra) were measured. With H2, Rd and 3H2O Ra were similar. With H3, 3H2O Ra, equal to glycolysis, was 65% of Rd. In study 2, six different subjects underwent a 3-h, 40 mU.m-2 x min-1 euglycemic insulin clamp. [6,6-2H2]glucose was infused throughout and H3 was infused during the last hour of the study. Open muscle biopsies were obtained at 150 and 180 min. Glycogen synthesis was assessed by three independent means: 1) direct measurement, as 3H disintegrations per minute in isolated muscle glycogen per plasma H3 specific activity; 2) extrapolation from the activity of glycogen synthase assayed in the presence of the concentrations of glucose 6-phosphate and UDP-glucose measured in the biopsy; and 3) the difference between Rd and glycolysis. Despite a wide range in Rd [24.5-58.8 mumol.kg fat-free mass (FFM)-1 x min-1] and glycolysis (14.2-26.1), the three methods yielded similar results of 20.0 +/- 3.9, 22.5 +/- 3.7, and 20.6 +/- 3.7 mumol.kg FFM-1 x min-1 and correlated highly with each other (r2 = 0.92-0.96). Our results (study 1) indicate that the rate of plasma tritiated water formation reflects the intracellular detritiation of tritiated glucose. Under hyperinsulinemic conditions (study 2) the net rate of muscle glycogen synthesis can be accurately estimated from the glycogen synthase activity and from the difference between total glucose uptake and glycolysis. Thus, at high physiological plasma insulin concentrations resulting in submaximal stimulation of muscle glycogen synthesis, the latter can be accurately measured in humans.

Insulin promotes glycogen synthesis in the absence of GSK3 phosphorylation in skeletal muscle

2008 ◽  
Vol 294 (1) ◽  
pp. E28-E35 ◽  
Author(s):  
Michale Bouskila ◽  
Michael F. Hirshman ◽  
Jørgen Jensen ◽  
Laurie J. Goodyear ◽  
Kei Sakamoto
Keyword(s):  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Muscle Glycogen ◽  
Glycogen Content ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Wild Type ◽  
Muscle Glycogen Synthesis ◽  
Mutant Forms

Insulin promotes dephosphorylation and activation of glycogen synthase (GS) by inactivating glycogen synthase kinase (GSK) 3 through phosphorylation. Insulin also promotes glucose uptake and glucose 6-phosphate (G-6- P) production, which allosterically activates GS. The relative importance of these two regulatory mechanisms in the activation of GS in vivo is unknown. The aim of this study was to investigate if dephosphorylation of GS mediated via GSK3 is required for normal glycogen synthesis in skeletal muscle with insulin. We employed GSK3 knockin mice in which wild-type GSK3α and -β genes are replaced with mutant forms (GSK3α/βS21A/S21A/S9A/S9A), which are nonresponsive to insulin. Although insulin failed to promote dephosphorylation and activation of GS in GSK3α/βS21A/S21A/S9A/S9Amice, glycogen content in different muscles from these mice was similar compared with wild-type mice. Basal and epinephrine-stimulated activity of muscle glycogen phosphorylase was comparable between wild-type and GSK3 knockin mice. Incubation of isolated soleus muscle in Krebs buffer containing 5.5 mM glucose in the presence or absence of insulin revealed that the levels of G-6- P, the rate of [14C]glucose incorporation into glycogen, and an increase in total glycogen content were similar between wild-type and GSK3 knockin mice. Injection of glucose containing 2-deoxy-[3H]glucose and [14C]glucose also resulted in similar rates of muscle glucose uptake and glycogen synthesis in vivo between wild-type and GSK3 knockin mice. These results suggest that insulin-mediated inhibition of GSK3 is not a rate-limiting step in muscle glycogen synthesis in mice. This suggests that allosteric regulation of GS by G-6- P may play a key role in insulin-stimulated muscle glycogen synthesis in vivo.

Increased lipid oxidation but normal muscle glycogen response to epinephrine in humans with IDDM

1996 ◽  
Vol 271 (2) ◽  
pp. E284-E293 ◽  
Author(s):  
N. Cohen ◽  
M. Halberstam ◽  
L. Rossetti ◽  
H. Shamoon
Keyword(s):  
Skeletal Muscle ◽  
Lipid Oxidation ◽  
Glucose Uptake ◽  
Muscle Glycogen ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Glycogen Metabolism ◽  
Whole Body ◽  
Dependent Diabetes Mellitus ◽  
Skeletal Muscle Glycogen

The effects of physiological increments in epinephrine and insulin on glucose production (GP), skeletal muscle glycogen metabolism, and substrate oxidation were studied in eight insulin-dependent diabetes mellitus (IDDM) and nine control subjects. Epinephrine was coinfused for the final 120 min of a 240-min euglycemic, hyperinsulinemic clamp. In both groups, insulin increased glucose uptake, glycogen synthesis, and whole body carbohydrate (CHO) oxidation and inhibited GP (by 70-80%) and lipid oxidation (by approximately 50%), whereas epinephrine antagonized the effect of insulin on glucose uptake and glycogen synthesis. In contrast, GP increased in IDDM subjects (P < 0.02) but remained suppressed by insulin in controls. CHO oxidation fell (1.37 +/- 0.25 vs. 2.08 +/- 0.32 mg.kg-1.min-1) and lipid oxidation increased to baseline in IDDM subjects, with increments in plasma free fatty acids (FFA) and glycerol. In contrast, in controls, plasma FFA and glycerol remained suppressed and lipid oxidation decreased further with epinephrine (P < 0.005). Epinephrine completely reversed insulin's activation of muscle glycogen synthase in both groups. Thus, during hyperinsulinemia, the hepatic response to epinephrine in IDDM subjects may be dependent on activation of lipid oxidation. Skeletal muscle glycogen metabolism is exquisitely sensitive to epinephrine despite the presence of hyperinsulinemia.

Plasma glucose concentration determines direct versus indirect liver glycogen synthesis

1986 ◽  
Vol 251 (5) ◽  
pp. E584-E590 ◽  
Author(s):  
C. H. Lang ◽  
G. J. Bagby ◽  
H. L. Blakesley ◽  
J. L. Johnson ◽  
J. J. Spitzer
Keyword(s):  
Plasma Glucose ◽  
Glucose Concentration ◽  
Infusion Rate ◽  
Glycogen Synthesis ◽  
Liver Glycogen ◽  
Glucose Infusion ◽  
Glucose Infusion Rate ◽  
Hepatic Glycogen ◽  
Glucose Load ◽  
Indirect Pathway

In the present study hepatic glycogenesis by the direct versus indirect pathway was determined as a function of the glucose infusion rate. Glycogen synthesis was examined in catheterized conscious rats that had been fasted 48 h before receiving a 3-h infusion (iv) of glucose. Glucose, containing tracer quantities of [U-14C]- and [6-3H]glucose, was infused at rates ranging from 0 to 230 mumol X min-1 X kg-1. Plasma concentrations of glucose, lactate, and insulin were positively correlated with the glucose infusion rate. Despite large changes in plasma glucose, lactate, and insulin concentrations, the rate of hepatic glycogen deposition (0.46 +/- 0.03 mumol X min-1 X g-1) did not vary significantly between glucose infusion rates of 20 and 230 mumol X min-1 X kg-1. However, the percent contribution of the direct pathway to glycogen repletion gradually increased from 13 +/- 2 to 74 +/- 4% in the lowest to the highest glucose infusion rates, with prevailing plasma glucose concentrations from 9.4 +/- 0.5 to 21.5 +/- 2.1 mM. Endogenous glucose production was depressed (by up to 40%), but not abolished by the glucose infusions. Only a small fraction (7-14%) of the infused glucose load was incorporated into liver glycogen via the direct pathway irrespective of the glucose infusion rate. Our data indicate that the relative contribution of the direct and indirect pathways of hepatic glycogen synthesis are dependent on the glucose load or plasma glucose concentration and emphasize the predominance of the indirect pathway of glycogenesis at plasma glucose concentrations normally observed after feeding.

Glucose infusion causes insulin resistance in skeletal muscle of rats without changes in Akt and AS160 phosphorylation

2007 ◽  
Vol 293 (5) ◽  
pp. E1358-E1364 ◽  
Author(s):  
Andrew J. Hoy ◽  
Clinton R. Bruce ◽  
Anna Cederberg ◽  
Nigel Turner ◽  
David E. James ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Insulin Signaling ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Glucose Infusion ◽  
Metabolic Effects ◽  
Synthesis Rate ◽  
Muscle Sample

Hyperglycemia is a defining feature of Type 1 and 2 diabetes. Hyperglycemia also causes insulin resistance, and our group (Kraegen EW, Saha AK, Preston E, Wilks D, Hoy AJ, Cooney GJ, Ruderman NB. Am J Physiol Endocrinol Metab Endocrinol Metab 290: E471–E479, 2006) has recently demonstrated that hyperglycemia generated by glucose infusion results in insulin resistance after 5 h but not after 3 h. The aim of this study was to investigate possible mechanism(s) by which glucose infusion causes insulin resistance in skeletal muscle and in particular to examine whether this was associated with changes in insulin signaling. Hyperglycemia (∼10 mM) was produced in cannulated male Wistar rats for up to 5 h. The glucose infusion rate required to maintain this hyperglycemia progressively lessened over 5 h (by 25%, P < 0.0001 at 5 h) without any alteration in plasma insulin levels consistent with the development of insulin resistance. Muscle glucose uptake in vivo (44%; P < 0.05) and glycogen synthesis rate (52%; P < 0.001) were reduced after 5 h compared with after 3 h of infusion. Despite these changes, there was no decrease in the phosphorylation state of multiple insulin signaling intermediates [insulin receptor, Akt, AS160 (Akt substrate of 160 kDa), glycogen synthase kinase-3β] over the same time course. In isolated soleus strips taken from control or 1- or 5-h glucose-infused animals, insulin-stimulated 2-deoxyglucose transport was similar, but glycogen synthesis was significantly reduced in the 5-h muscle sample (68% vs. 1-h sample; P < 0.001). These results suggest that the reduced muscle glucose uptake in rats after 5 h of acute hyperglycemia is due more to the metabolic effects of excess glycogen storage than to a defect in insulin signaling or glucose transport.

scholarly journals Akt2 influences glycogen synthase activity in human skeletal muscle through regulation of NH2-terminal (sites 2 + 2a) phosphorylation

2013 ◽  
Vol 304 (6) ◽  
pp. E631-E639 ◽  
Author(s):  
Martin Friedrichsen ◽  
Jesper B. Birk ◽  
Erik A. Richter ◽  
Rasmus Ribel-Madsen ◽  
Christian Pehmøller ◽  
...  
Keyword(s):  
Insulin Signaling ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Fine Tuning ◽  
Whole Body ◽  
Euglycemic Hyperinsulinemic Clamp ◽  
Negatively Associated ◽  
Molecular Events ◽  
Muscle Glycogen Synthesis ◽  
Key Enzyme

Type 2 diabetes is characterized by reduced muscle glycogen synthesis. The key enzyme in this process, glycogen synthase (GS), is activated via proximal insulin signaling, but the exact molecular events remain unknown. Previously, we demonstrated that phosphorylation of Thr308 on Akt (p-Akt-Thr308), Akt2 activity, and GS activity in muscle were positively associated with insulin sensitivity. Here, in the same study population, we determined the influence of several upstream elements in the canonical PI3K signaling on muscle GS activation. One-hundred eighty-one nondiabetic twins were examined with the euglycemic hyperinsulinemic clamp combined with excision of muscle biopsies. Insulin signaling was evaluated at the levels of the insulin receptor, IRS-1-associated PI3K (IRS-1-PI3K), Akt, and GS employing activity assays and phosphospecific Western blotting. The insulin-stimulated GS activity was positively associated with p-Akt-Thr308 ( P = 0.01) and Akt2 activity ( P = 0.04) but not p-Akt-Ser473 or IRS-1-PI3K activity. Furthermore, p-Akt-Thr308 and Akt2 activity were negatively associated with NH2-terminal GS phosphorylation ( P = 0.001 for both), which in turn was negatively associated with insulin-stimulated GS activity ( P < 0.001). We found no association between COOH-terminal GS phosphorylation and Akt or GS activity. Employing whole body Akt2-knockout mice, we validated the necessity for Akt2 in insulin-mediated GS activation. However, since insulin did not affect NH2-terminal phosphorylation in mice, we could not use this model to validate the observed association between GS NH2-terminal phosphorylation and Akt activity in humans. In conclusion, our study suggests that although COOH-terminal dephosphorylation is likely necessary for GS activation, Akt2-dependent NH2-terminal dephosphorylation may be the site for “fine-tuning” insulin-mediated GS activation in humans.

Flux control in the rat gastrocnemius glycogen synthesis pathway by in vivo13C/31P NMR spectroscopy

2001 ◽  
Vol 280 (4) ◽  
pp. E598-E607 ◽  
Author(s):  
J. R. Chase ◽  
D. L. Rothman ◽  
R. G. Shulman
Keyword(s):  
Glucose Transport ◽  
Muscle Glycogen ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Synthesis Rate ◽  
31P Nmr Spectroscopy ◽  
Control Analysis ◽  
Control Coefficient ◽  
Flux Control ◽  
Muscle Glycogen Synthesis

To determine the relative contributions of glucose transport/hexokinase, glycogen synthase (GSase), and glycolysis to the control of insulin-stimulated muscle glycogen synthesis, we combined13C and 31P NMR to quantitate the glycogen synthesis rate and glucose 6-phosphate (G-6- P) levels in rat (Sprague-Dawley) gastrocnemius muscle during hyperinsulinemia at euglycemic (E) and hyperglycemic (H) glucose concentrations under thiopental anesthesia. Flux control was calculated using metabolic control analysis. The combined control coefficient of glucose transport/hexokinase (GT/Hk) for glycogen synthesis was 1.1 ± 0.03 (direct measure) and 1.14–1.16 (calculated for a range of glycolytic fluxes), whereas the control coefficient for GSase was much lower (0.011–0.448). We also observed that the increase in in vivo [G-6- P] from E to H (0.22 ± 0.03 to 0.40 ± 0.03 mM) effects a supralinear increase in the in vitro velocity of GSase, from 14.6 to 26.1 mU · kg−1 · min−1 (1.8-fold). All measurements suggest that the majority of the flux control of muscle glycogen synthesis is at the GT/Hk step.

scholarly journals Effect of acute activation of 5′-AMP-activated protein kinase on glycogen regulation in isolated rat skeletal muscle

2007 ◽  
Vol 102 (3) ◽  
pp. 1007-1013 ◽  
Author(s):  
Licht Miyamoto ◽  
Taro Toyoda ◽  
Tatsuya Hayashi ◽  
Shin Yonemitsu ◽  
Masako Nakano ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Muscle Glycogen ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Glycolytic Flux ◽  
Ampk Activation ◽  
Ampk Activity ◽  
Amp Activated Protein Kinase ◽  
Isolated Rat

5′-AMP-activated protein kinase (AMPK) has been implicated in glycogen metabolism in skeletal muscle. However, the physiological relevance of increased AMPK activity during exercise has not been fully clarified. This study was performed to determine the direct effects of acute AMPK activation on muscle glycogen regulation. For this purpose, we used an isolated rat muscle preparation and pharmacologically activated AMPK with 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR). Tetanic contraction in vitro markedly activated the α1- and α2-isoforms of AMPK, with a corresponding increase in the rate of 3- O-methylglucose uptake. Incubation with AICAR elicited similar enhancement of AMPK activity and 3- O-methylglucose uptake in rat epitrochlearis muscle. In contrast, whereas contraction stimulated glycogen synthase (GS), AICAR treatment decreased GS activity. Insulin-stimulated GS activity also decreased after AICAR treatment. Whereas contraction activated glycogen phosphorylase (GP), AICAR did not alter GP activity. The muscle glycogen content decreased in response to contraction but was unchanged by AICAR. Lactate release was markedly increased when muscles were stimulated with AICAR in buffer containing glucose, indicating that the glucose taken up into the muscle was catabolized via glycolysis. Our results suggest that AMPK does not mediate contraction-stimulated glycogen synthesis or glycogenolysis in skeletal muscle and also that acute AMPK activation leads to an increased glycolytic flux by antagonizing contraction-stimulated glycogen synthesis.

Mechanism of muscle glycogen autoregulation in humans

2000 ◽  
Vol 278 (4) ◽  
pp. E663-E668 ◽  
Author(s):  
Didier Laurent ◽  
Ripudaman S. Hundal ◽  
Alan Dresner ◽  
Thomas B. Price ◽  
Suzanne M. Vogel ◽  
...  
Keyword(s):  
Muscle Glycogen ◽  
Feedback Inhibition ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Plasma Free Fatty Acid ◽  
Whole Body ◽  
Resonance Spectroscopy ◽  
Twofold Increase ◽  
Oxidation Rates ◽  
Before And After

To examine the mechanism by which muscle glycogen limits its own synthesis, muscle glycogen and glucose 6-phosphate (G-6- P) concentrations were measured in seven healthy volunteers during a euglycemic (∼5.5 mM)-hyperinsulinemic (∼450 pM) clamp using 13C/31P nuclear magnetic resonance spectroscopy before and after a muscle glycogen loading protocol. Rates of glycogen synthase ( V syn) and phosphorylase ( V phos) flux were estimated during a [1-13C]glucose (pulse)-unlabeled glucose (chase) infusion. The muscle glycogen loading protocol resulted in a 65% increase in muscle glycogen content that was associated with a twofold increase in fasting plasma lactate concentrations ( P < 0.05 vs. basal) and an ∼30% decrease in plasma free fatty acid concentrations ( P < 0.001 vs. basal). Muscle glycogen loading resulted in an ∼30% decrease in the insulin-stimulated rate of net muscle glycogen synthesis ( P < 0.05 vs. basal), which was associated with a twofold increase in intramuscular G-6- P concentration ( P < 0.05 vs. basal). Muscle glycogen loading also resulted in an ∼30% increase in whole body glucose oxidation rates ( P < 0.05 vs. basal), whereas there was no effect on insulin-stimulated rates of whole body glucose uptake (∼10.5 mg ⋅ kg body wt−1 ⋅ min−1 for both clamps) or glycogen turnover ( V syn/ V phos was ∼23% for both clamps). In conclusion, these data are consistent with the hypothesis that glycogen limits its own synthesis through feedback inhibition of glycogen synthase activity, as reflected by an accumulation of intramuscular G-6- P, which is then shunted into aerobic and anaerobic glycolysis.

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