title: Portal glucose delivery stimulates muscle but not liver protein metabolism.
abstract: 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 [(14)C]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.
authors.affiliation: Dept. of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-6015, USA.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Kraft
authors.forename: Katie C
authors.initials: KC
authors.lastname: Coate
authors.forename: Dominique
authors.initials: D
authors.lastname: Dardevet
authors.forename: Ben
authors.initials: B
authors.lastname: Farmer
authors.forename: E Patrick
authors.initials: EP
authors.lastname: Donahue
authors.forename: Phillip E
authors.initials: PE
authors.lastname: Williams
authors.forename: Alan D
authors.initials: AD
authors.lastname: Cherrington
authors.forename: Mary Courtney
authors.initials: MC
authors.lastname: Moore
mesh_terms: D026962:Amino Acid Transport System ASC / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004285:Dogs; D004750:Enteral Nutrition; D005947:Glucose / Q000008:administration & dosage* / Q000378:metabolism / Q000493:pharmacokinetics; D007262:Infusions, Intravenous; D027283:Large Neutral Amino Acid-Transporter 1 / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D010766:Phosphorylation; D011169:Portal Vein; D019518:Postprandial Period; D014176:Protein Biosynthesis / Q000187:drug effects; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism
chemical_list: D026962:Amino Acid Transport System ASC; D000596:Amino Acids; D027283:Large Neutral Amino Acid-Transporter 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C448959:ribosomal protein S6 kinase, 70kD, polypeptide 2; D005947:Glucose