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Am J Physiol Endocrinol Metab. 2016 Oct 1;311(4):E671-E677. doi: 10.1152/ajpendo.00120.2016. Epub 2016 Aug 16.

Insulin does not stimulate muscle protein synthesis during increased plasma branched-chain amino acids alone but still decreases whole body proteolysis in humans.

Author information

1
Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona.
2
Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona; Mayo Clinic in Arizona, Scottsdale, Arizona; and.
3
Midwestern University, Glendale, Arizona.
4
Center for Metabolic and Vascular Biology, Arizona State University, Tempe, Arizona; Mayo Clinic in Arizona, Scottsdale, Arizona; and christos.katsanos@asu.edu.

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.

KEYWORDS:

branched-chain amino acid clearance; branched-chain amino acids; branched-chain amino acids and insulin; protein breakdown; protein synthesis

PMID:
27530230
PMCID:
PMC5241558
DOI:
10.1152/ajpendo.00120.2016
[Indexed for MEDLINE]
Free PMC Article

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