title: Effect of gluteus medius muscle sample collection depth on postprandial mammalian target of rapamycin signaling in mature Thoroughbred mares.
abstract: OBJECTIVE
  To determine the effect of biopsy collection depth on the postprandial activation of mammalian target of rapamycin (mTOR) signaling factors, particularly protein kinase B, ribosomal protein S6 kinase, ribosomal protein S6, and eukaryotic initiation factor 4E binding protein 1 in middle-aged horses.
  
  
  METHODS
  6 healthy Thoroughbred mares (mean ± SD age, 13.4 ± 3.4 years).
  
  
  METHODS
  Horses were fed a high-protein feed at 3 g/kg. Sixty minutes after horses were fed, the percutaneous needle biopsy technique was used to collect biopsy specimens from the gluteus medius muscle at 6, 8, and 10 cm below the surface of the skin. Muscle specimens were analyzed for the activation of upstream and downstream mTOR signaling factors, myosin heavy chain (MHC) isoform composition, and amino acid concentrations.
  
  
  RESULTS
  A 21% increase in MHC IIA isoform expression and a 21% decrease in MHC IIX isoform expression were identified as biopsy depth increased from 8 to 10 cm below the surface of the skin; however, no significant change was evident in the degree of MHC I expression with muscle depth. Biopsy depth had no significant effect on the phosphorylation of any of the mTOR signaling factors evaluated.
  
  
  CONCLUSIONS
  Postprandial mTOR signaling could be compared between middle-aged horses when biopsy specimens were collected between 6 and 10 cm below the surface of the skin. Optimization of muscle biopsy techniques for evaluating mTOR signaling in horses will facilitate the design of future investigations into the factors that regulate muscle mass in horses.
authors.affiliation: Department of Animal and Food Sciences, College of Veterinary Medicine, University of Kentucky, Lexington, KY 40546, USA.
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Wagner
authors.forename: Kristine L
authors.initials: KL
authors.lastname: Urschel
authors.forename: Mellani
authors.initials: M
authors.lastname: Lefta
authors.forename: Karyn A
authors.initials: KA
authors.lastname: Esser
mesh_terms: D000818:Animals; D001707:Biopsy, Needle; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D019518:Postprandial Period / Q000502:physiology*; D013048:Specimen Handling; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D058570:TOR Serine-Threonine Kinases