scholarly journals Portal glucose delivery stimulates muscle but not liver protein metabolism

2012 ◽  
Vol 303 (10) ◽  
pp. E1202-E1211 ◽  
Author(s):  
Guillaume Kraft ◽  
Katie C. Coate ◽  
Dominique Dardevet ◽  
Ben Farmer ◽  
E. Patrick Donahue ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Portal Vein ◽  
Glucose Uptake ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Glycogen Storage ◽  
Glucose Infusion ◽  
Nutrition Support ◽  
Liver Protein ◽  
Skeletal Muscle Protein

Portal vein glucose delivery (the portal glucose signal) stimulates glucose uptake and glycogen storage by the liver, whereas portal amino acid (AA) delivery (the portal AA signal) induces an increase in protein synthesis by the liver. During a meal, both signals coexist and may interact. In this study, we compared the protein synthesis rates in the liver and muscle in response to portal or peripheral glucose infusion during intraportal infusion of a complete AA mixture. Dogs were surgically prepared with hepatic sampling catheters and flow probes. After a 42-h fast, they underwent a 3-h hyperinsulinemic (4× basal) hyperglucagonemic (3× basal) hyperglycemic (≈160 mg/dl) hyperaminoacidemic (hepatic load 1.5× basal; delivered intraportally) clamp (postprandial conditions). Glucose was infused either via a peripheral (PeG; n = 7) or the portal vein (PoG; n = 8). Protein synthesis was assessed with a primed, continuous [14C]leucine infusion. Net hepatic glucose uptake was stimulated by portal glucose infusion (+1 mg·kg−1·min−1, P < 0.05) as expected, but hepatic fractional AA extraction and hepatic protein synthesis did not differ between groups. There was a lower arterial AA concentration in the PoG group (−19%, P < 0.05) and a significant stimulation (+30%) of muscle protein synthesis associated with increased expression of LAT1 and ASCT2 AA transporters and p70S6 phosphorylation. Concomitant portal glucose and AA delivery enhances skeletal muscle protein synthesis compared with peripheral glucose and portal AA delivery. These data suggest that enteral nutrition support may have an advantage over parenteral nutrition in stimulating muscle protein synthesis.

Glucose flux is normalized by compensatory hyperinsulinaemia in growth hormone-induced insulin resistance in healthy subjects, while skeletal muscle protein synthesis remains unchanged

2002 ◽  
Vol 102 (4) ◽  
pp. 457-464 ◽  
Author(s):  
Jonas NYGREN ◽  
Anders THORELL ◽  
Kerstin BRISMAR ◽  
Pia ESSÉN ◽  
Jan WERNERMAN ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Glucose Infusion ◽  
Skeletal Muscle Protein ◽  
Gh Treatment ◽  
Glucose Flux ◽  
Skeletal Muscle Protein Synthesis ◽  
Igf Binding

The aim of this present investigation was to study the relationship between the reduction in insulin sensitivity accompanying 5 days of treatment with growth hormone (GH; 0.05mgċ24h-1ċkg-1) and intracellular substrate oxidation rates in six healthy subjects, while maintaining glucose flux by a constant glucose infusion and adjusting insulin infusion rates to achieve normoglycaemia (feedback clamp). Protein synthesis rates in skeletal muscle (flooding dose of L-[2H5]phenylalanine) were determined under these conditions. We also compared changes in insulin sensitivity after GH treatment with simultaneous changes in energy requirements, protein synthesis rates, nitrogen balance, 3-methylhistidine excretion in urine, body composition and the hormonal milieu. After GH treatment, 70% more insulin was required to maintain normoglycaemia (P < 0.01). The ratio between glucose infusion rate and serum insulin levels decreased by 34% at the two levels of glucose infusion tested (P < 0.05). Basal levels of C-peptide, insulin-like growth factor (IGF)-I and IGF-binding protein-3 increased almost 2-fold, while levels of glucose, insulin, glucagon, GH and IGF-binding protein-1 remained unchanged. Non-esterified fatty acid levels decreased (P < 0.05). In addition, 24h urinary nitrogen excretion decreased by 26% (P < 0.01) after GH treatment, while skeletal muscle protein synthesis and 3-methylhistidine excretion in urine remained unchanged. Energy expenditure increased by 5% (P < 0.05) after treatment, whereas fat and carbohydrate oxidation were unaltered. In conclusion, when glucose flux was normalized by compensatory hyperinsulinaemia under conditions of GH-induced insulin resistance, intracellular rates of oxidation of glucose and fat remained unchanged. The nitrogen retention accompanying GH treatment seems to be due largely to improved nitrogen balance in non-muscle tissue.

Insulin stimulates muscle protein synthesis in neonates during endotoxemia despite repression of translation initiation

2007 ◽  
Vol 292 (2) ◽  
pp. E629-E636 ◽  
Author(s):  
Renan A. Orellana ◽  
Scot R. Kimball ◽  
Agus Suryawan ◽  
Jeffery Escobar ◽  
Hanh V. Nguyen ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Translation Initiation ◽  
Translational Control ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Control Mechanisms ◽  
Liver Protein ◽  
Skeletal Muscle Protein ◽  
Longissimus Dorsi Muscle ◽  
Neonatal Pigs

Skeletal muscle protein synthesis is reduced in neonatal pigs in response to endotoxemia. To examine the role of insulin in this response, neonatal pigs were infused with endotoxin (LPS, 0 and 10 μg·kg−1·h−1), whereas glucose and amino acids were maintained at fasting levels and insulin was clamped at fasting or fed (2 or 10 μU/ml) levels. Fractional rates of protein synthesis and translational control mechanisms were examined in longissimus dorsi muscle and liver. In the presence of fasting insulin, LPS reduced muscle protein synthesis (−29%), and increasing insulin to fed levels accelerated muscle protein synthesis in both groups (controls, +44%; LPS, +64%). LPS, but not insulin, increased liver protein synthesis by +28%. In muscle of fasting neonatal pigs, LPS reduced 4E-BP1 phosphorylation and eIF4E to eIF4G binding. In muscle of controls, but not LPS pigs, raising insulin to fed levels increased 4E-BP1 and S6K1 phosphorylation and eIF4E to eIF4G binding. In muscle and liver, neither LPS nor insulin altered eIF2B activity. eEF2 phosphorylation decreased in response to insulin in both LPS and control animals. The results suggest that, in endotoxemic neonatal animals, the response of protein synthesis to insulin is maintained despite suppression of mTOR-dependent translation initiation and eIF4E availability for eIF4F assembly. Maintenance of an anabolic response to the feeding-induced rise in insulin likely exerts a protective effect for the neonate to the catabolic processes induced by sepsis.

scholarly journals Resistance exercise maintains skeletal muscle protein synthesis during bed rest

1997 ◽  
Vol 82 (3) ◽  
pp. 807-810 ◽  
Author(s):  
Arny A. Ferrando ◽  
Kevin D. Tipton ◽  
Marcas M. Bamman ◽  
Robert R. Wolfe
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Resistance Training ◽  
Resistance Exercise ◽  
Lean Body Mass ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Bed Rest ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis

Ferrando, Arny A., Kevin D. Tipton, Marcas M. Bamman, and Robert R. Wolfe. Resistance exercise maintains skeletal muscle protein synthesis during bed rest. J. Appl. Physiol. 82(3): 807–810, 1997.—Spaceflight results in a loss of lean body mass and muscular strength. A ground-based model for microgravity, bed rest, results in a loss of lean body mass due to a decrease in muscle protein synthesis (MPS). Resistance training is suggested as a proposed countermeasure for spaceflight-induced atrophy because it is known to increase both MPS and skeletal muscle strength. We therefore hypothesized that scheduled resistance training throughout bed rest would ameliorate the decrease in MPS. Two groups of healthy volunteers were studied during 14 days of simulated microgravity. One group adhered to strict bed rest (BR; n = 5), whereas a second group engaged in leg resistance exercise every other day throughout bed rest (BREx; n = 6). MPS was determined directly by the incorporation of infusedl-[ ring-13C6]phenylalanine into vastus lateralis protein. After 14 days of bed rest, MPS in the BREx group did not change and was significantly greater than in the BR group. Thus moderate-resistance exercise can counteract the decrease in MPS during bed rest.

Growth hormone acutely stimulates forearm muscle protein synthesis in normal humans

1991 ◽  
Vol 260 (3) ◽  
pp. E499-E504 ◽  
Author(s):  
D. A. Fryburg ◽  
R. A. Gelfand ◽  
E. J. Barrett
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Growth Hormone ◽  
Protein Synthesis ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis ◽  
Igf I ◽  
Normal Humans

The short-term effects of growth hormone (GH) on skeletal muscle protein synthesis and degradation in normal humans are unknown. We studied seven postabsorptive healthy men (age 18-23 yr) who received GH (0.014 micrograms.kg-1.min-1) via intrabrachial artery infusion for 6 h. The effects of GH on forearm amino acid and glucose balances and on forearm amino acid kinetics [( 3H]Phe and [14C]Leu) were determined after 3 and 6 h of the GH infusion. Forearm deep vein GH rose to 35 +/- 6 ng/ml in response to GH, whereas systemic levels of GH, insulin, and insulin-like growth factor I (IGF-I) were unchanged. Forearm glucose uptake did not change during the study. After 6 h, GH suppressed forearm net release (3 vs. 6 h) of Phe (P less than 0.05), Leu (P less than 0.01), total branched-chain amino acids (P less than 0.025), and essential neutral amino acids (0.05 less than P less than 0.1). The effect on the net balance of Phe and Leu was due to an increase in the tissue uptake for Phe (71%, P less than 0.05) and Leu (37%, P less than 0.005) in the absence of any significant change in release of Phe or Leu from tissue. In the absence of any change in systemic GH, IGF-I, or insulin, these findings suggest that locally infused GH stimulates skeletal muscle protein synthesis. These findings have important physiological implications for both the role of daily GH pulses and the mechanisms through which GH can promote protein anabolism.

scholarly journals Changes in skeletal muscle protein synthesis in trained adults during recovery from endurance exercise

2008 ◽  
Vol 22 (S1) ◽  
Author(s):  
Lisa Vislocky ◽  
P. Courtney Gaine ◽  
Matthew Pikosky ◽  
Douglas Bolster ◽  
Arny Ferrando ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Endurance Exercise ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis

scholarly journals Amino Acid Trafficking and Skeletal Muscle Protein Synthesis: A Case of Supply and Demand

2021 ◽  
Vol 9 ◽  
Author(s):  
James P. White
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Energy Production ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Supply And Demand ◽  
Mechanical Stimuli ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis ◽  
Branched Chain

Skeletal muscle protein synthesis is a highly complex process, influenced by nutritional status, mechanical stimuli, repair programs, hormones, and growth factors. The molecular aspects of protein synthesis are centered around the mTORC1 complex. However, the intricacies of mTORC1 regulation, both up and downstream, have expanded overtime. Moreover, the plastic nature of skeletal muscle makes it a unique tissue, having to coordinate between temporal changes in myofiber metabolism and hypertrophy/atrophy stimuli within a tissue with considerable protein content. Skeletal muscle manages the push and pull between anabolic and catabolic pathways through key regulatory proteins to promote energy production in times of nutrient deprivation or activate anabolic pathways in times of nutrient availability and anabolic stimuli. Branched-chain amino acids (BCAAs) can be used for both energy production and signaling to induce protein synthesis. The metabolism of BCAAs occur in tandem with energetic and anabolic processes, converging at several points along their respective pathways. The fate of intramuscular BCAAs adds another layer of regulation, which has consequences to promote or inhibit muscle fiber protein anabolism. This review will outline the general mechanisms of muscle protein synthesis and describe how metabolic pathways can regulate this process. Lastly, we will discuss how BCAA availability and demand coordinate with synthesis mechanisms and identify key factors involved in intramuscular BCAA trafficking.

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