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Validation of a Technique for Measuring Muscle Protein Synthesis In Vivo in the Horse
Author(s) -
Naylor R.J.,
Smith K.,
Blake V.,
Rankin D.,
Atherton P.,
Piercy R.J.
Publication year - 2014
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/evj.12323_43
Subject(s) - horse , phenylalanine , chemistry , in vivo , myofibril , amino acid , steady state (chemistry) , biochemistry , biology , paleontology , microbiology and biotechnology
Reasons for performing the study Measurement of incorporation of stable isotope‐containing amino acids into muscle is the gold‐standard technique for measuring muscle protein synthesis ( MPS ), but its use in horses has not been evaluated. Objectives 1) To establish a technique for measuring MPS in vivo in the horse using a labelled amino acid tracer and 2) to determine basal MPS in the horse using this technique. Methods Three mature Thoroughbred geldings received 0.1 mg/kg bwt D 5‐phenylalanine ( D 5‐Phe) i.v. and plasma D 5‐Phe enrichment was measured over 3 h. Pharmacokinetic modelling determined the rate of appearance and phenylalanine pool size, from which a loading dose and infusion rate that would achieve a steady 5–10% plasma enrichment were calculated. Subsequently, steady‐state was confirmed by measuring plasma enrichment during 6 h of infusion and the effect of treadmill exercise and sedation (0.4 mg/kg bwt) were also determined. Horses subsequently received the calculated D 5‐Phe infusion rate and skeletal muscle biopsy samples were collected after 1 and 3 h, allowing basal MPS to be calculated. Precursor intramuscular phe labelling was measured by GC‐MS and tracer phe incorporation into muscle myofibrillar protein was determined using GC ‐pyrolysis‐ IRMS to calculate fractional synthetic rate. Results The mean rate of whole body phenylalanine appearance in the horse was 56 μmol/kg bwt/h (s.d. 24) and mean phenylalanine pool size 41 μmol/kg bwt (s.d. 8.8). From this a priming dose of 3.3 μmol/kg bwt and an infusion rate of 4.5 μmol/kg bwt/h D 5‐Phenylalanine was calculated and subsequently confirmed to achieve steady state tracer enrichment from 5.6–9.1 APE in sedentary horses. Exercise caused a transitory, and sedation a more prolonged reduction in plasma enrichment (up to 20%). D 5‐Phe incorporation revealed a basal FSR of 0.029%/h (s.d. 0.013) in the horse. Conclusions D 5‐Phenylalanine is a suitable amino acid tracer for measurement of MPS in the horse yielding rates of MPS in line with other large mammals. Ethical animal research: The study was performed with local Ethics Committee approval and Home Office project license ( PPL 70/7523) under the UK A( SP )A Act 1986. Sources of funding: This work was generously funded by B oehringer I ngelheim. Competing interests: None.