title: Insulin does not stimulate muscle protein synthesis during increased plasma branched-chain amino acids alone but still decreases whole body proteolysis in humans.
abstract: Insulin stimulates muscle protein synthesis when the levels of total amino acids, or at least the essential amino acids, are at or above their postabsorptive concentrations. Among the essential amino acids, branched-chain amino acids (BCAA) have the primary role in stimulating muscle protein synthesis and are commonly sought alone to stimulate muscle protein synthesis in humans. Fourteen healthy young subjects were studied before and after insulin infusion to examine whether insulin stimulates muscle protein synthesis in relation to the availability of BCAA alone. One half of the subjects were studied in the presence of postabsorptive BCAA concentrations (control) and the other half in the presence of increased plasma BCAA (BCAA). Compared with that prior to the initiation of the insulin infusion, fractional synthesis rate of muscle protein (%/h) did not change (P > 0.05) during insulin in either the control (0.04 ± 0.01 vs 0.05 ± 0.01) or the BCAA (0.05 ± 0.02 vs. 0.05 ± 0.01) experiments. Insulin decreased (P < 0.01) whole body phenylalanine rate of appearance (μmol·kg-1·min-1), indicating suppression of muscle proteolysis, in both the control (1.02 ± 0.04 vs 0.76 ± 0.04) and the BCAA (0.89 ± 0.07 vs 0.61 ± 0.03) experiments, but the change was not different between the two experiments (P > 0.05). In conclusion, insulin does not stimulate muscle protein synthesis in the presence of increased circulating levels of plasma BCAA alone. Insulin's suppressive effect on proteolysis is observed independently of the levels of circulating plasma BCAA.
authors.affiliation: Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona.
authors.forename: Sarah
authors.initials: S
authors.lastname: Everman
authors.affiliation: Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona.
authors.forename: Christian
authors.initials: C
authors.lastname: Meyer
authors.affiliation: Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona; Mayo Clinic in Arizona, Scottsdale, Arizona; and.
authors.forename: Lee
authors.initials: L
authors.lastname: Tran
authors.affiliation: Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona; Mayo Clinic in Arizona, Scottsdale, Arizona; and.
authors.forename: Nyssa
authors.initials: N
authors.lastname: Hoffman
authors.affiliation: Midwestern University, Glendale, Arizona.
authors.forename: Chad C
authors.initials: CC
authors.lastname: Carroll
authors.affiliation: Midwestern University, Glendale, Arizona.
authors.forename: William L
authors.initials: WL
authors.lastname: Dedmon
authors.affiliation: Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona; Mayo Clinic in Arizona, Scottsdale, Arizona; and christos.katsanos@asu.edu.
authors.forename: Christos S
authors.initials: CS
authors.lastname: Katsanos
mesh_terms: D000597:Amino Acids, Branched-Chain / Q000097:blood / Q000494:pharmacology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D010649:Phenylalanine / Q000097:blood; D014176:Protein Biosynthesis / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects*; D055815:Young Adult
chemical_list: D000597:Amino Acids, Branched-Chain; D007004:Hypoglycemic Agents; D007328:Insulin; D009124:Muscle Proteins; D010649:Phenylalanine
keywords: branched-chain amino acid clearance; branched-chain amino acids; branched-chain amino acids and insulin; protein breakdown; protein synthesis