Timing of the initial muscle biopsy does not affect the measured muscle protein fractional synthesis rate during basal, postabsorptive conditions
Open Access
- 1 February 2010
- journal article
- research article
- Published by American Physiological Society in Journal of Applied Physiology
- Vol. 108 (2), 363-368
- https://doi.org/10.1152/japplphysiol.00957.2009
Abstract
The muscle protein fractional synthesis rate (FSR) is determined by monitoring the incorporation of an amino acid tracer into muscle protein during a constant-rate intravenous tracer infusion. Commonly two sequential muscle biopsies are obtained some time after starting the tracer infusion. However, other protocols, including those with an initial biopsy before starting the tracer infusion to measure the background enrichment and those with only a single biopsy after several hours of tracer infusion have been used. To assess the validity of these approaches, we compared the muscle protein FSR obtained by calculating the difference in [ ring-2H5]phenylalanine and [5,5,5-2H3]leucine incorporation into muscle protein at ∼3.5 h after starting the tracer infusion and 1) at 60 min; 2) before starting the tracer infusion (background enrichment); 3) a population average muscle protein background enrichment; and 4) by measuring the tracer incorporation into muscle protein at ∼3.5 h assuming essentially no background enrichment. Irrespective of the tracer used, the muscle protein FSR calculated from the difference in the muscle protein labeling several hours after starting the tracer infusion and either the labeling at 60 min or the background enrichment were not different (e.g., 0.049 ± 0.007%/h vs. 0.049 ± 0.007%/h, respectively, with [2H5]phenylalanine; P = 0.99). However, omitting the initial biopsy and assuming no background enrichment yielded average FSR values that were ∼15% (with [2H5]phenylalanine) to 80% (with [2H3]leucine) greater ( P ≤ 0.059); using a population average background enrichment reduced the difference to ∼3% ( P = 0.76) and 22% ( P = 0.52) with [2H5]phenylalanine and [2H3]leucine, respectively. We conclude that during basal, postabsorptive conditions, valid muscle protein FSR values can be obtained irrespective of the timing of the initial biopsy so long as the protein labeling in two sequential biopsies is measured whereas the single biopsy approach should be avoided.Keywords
This publication has 48 references indexed in Scilit:
- Translational signaling responses preceding resistance training-mediated myofiber hypertrophy in young and old humansJournal of Applied Physiology, 2009
- No major sex differences in muscle protein synthesis rates in the postabsorptive state and during hyperinsulinemia-hyperaminoacidemia in middle-aged adultsJournal of Applied Physiology, 2009
- Muscle Protein Synthesis and Balance Responsiveness to Essential Amino Acids Ingestion in the Presence of Elevated Plasma Free Fatty Acid ConcentrationsJournal of Clinical Endocrinology & Metabolism, 2009
- Amino Acid Supplementation Increases Lean Body Mass, Basal Muscle Protein Synthesis, and Insulin-Like Growth Factor-I Expression in Older WomenJournal of Clinical Endocrinology & Metabolism, 2009
- Rapamycin administration in humans blocks the contraction‐induced increase in skeletal muscle protein synthesisJournal Of Physiology-London, 2009
- Differential stimulation of myofibrillar and sarcoplasmic protein synthesis with protein ingestion at rest and after resistance exerciseJournal Of Physiology-London, 2009
- Immobilization induces anabolic resistance in human myofibrillar protein synthesis with low and high dose amino acid infusionJournal Of Physiology-London, 2008
- Sequential muscle biopsies during a 6-h tracer infusion do not affect human mixed muscle protein synthesis and muscle phenylalanine kineticsAmerican Journal of Physiology-Endocrinology and Metabolism, 2008
- Higher muscle protein synthesis in women than men across the lifespan, and failure of androgen administration to amend age‐related decrementsThe FASEB Journal, 2008
- Basal muscle intracellular amino acid kinetics in women and menAmerican Journal of Physiology-Endocrinology and Metabolism, 2007