title: Whole-body protein turnover in peritoneal dialysis patients: a comparison of the [15N]glycine end product and the [13C]leucine precursor methods.
abstract: BACKGROUND
  Two well-described methods for measuring whole-body protein turnover (WBPT) are the precursor method using a primed continuous infusion of [1-(13)C]leucine and the end-product method with a single oral dose of [(15)N]glycine. We previously measured the effects of amino acid (AA)-containing dialysate on protein anabolism in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) using the [1-(13)C]leucine technique. Here, we examine whether the less invasive [(15)N]glycine method could also be appropriate for studying nutritional interventions.
  
  
  METHODS
  We compared the results of WBPT measurements using a single oral dose of [(15)N]glycine with those obtained with the primed continuous infusion of [1-(13)C]leucine during AA and glucose (G) dialysis and G-only dialysis in 12 CAPD patients in the fed state.
  
  
  RESULTS
  The end-product method showed a wide variation for protein synthesis and breakdown measurements. It did not detect a small but significant increase in protein synthesis with AA-containing dialysate as shown by the precursor method. However, a significant relation was found between both methods for net protein synthesis (i.e. protein synthesis minus breakdown) during AA and G (r = 0.75, P = 0.005) or during G-only dialysis (r = 0.86, P < 0.001). The agreement between the two methods for the net protein balance was good [intra-class correlation coefficient (ICC) = 0.88] with G-only dialysate and moderate (ICC = 0.70) with AA and G dialysate.
  
  
  CONCLUSIONS
  While the precursor method shows less variation, the more convenient end-product method may be useful in larger groups of selected patients including those on PD.
authors.affiliation: Department of Internal Medicine, Erasmus MC's, University Medical Center Rotterdam, The Netherlands. h.tjiong@erasmusmc.nl
authors.forename: Hoey Lan
authors.initials: HL
authors.lastname: Tjiong
authors.forename: Roel
authors.initials: R
authors.lastname: Swart
authors.forename: Trinet
authors.initials: T
authors.lastname: Rietveld
authors.forename: Josias L
authors.initials: JL
authors.lastname: Wattimena
authors.forename: Wim C
authors.initials: WC
authors.lastname: Hop
authors.forename: Marien W
authors.initials: MW
authors.lastname: Fieren
authors.forename: Jacobus W
authors.initials: JW
authors.lastname: van den Berg
mesh_terms: D000328:Adult; D000368:Aged; D002247:Carbon Isotopes; D015314:Dialysis Solutions; D005260:Female; D005998:Glycine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D006801:Humans; D007930:Leucine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D009587:Nitrogen Isotopes; D010531:Peritoneal Dialysis, Continuous Ambulatory; D011506:Proteins / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D015314:Dialysis Solutions; D009587:Nitrogen Isotopes; D011506:Proteins; D007930:Leucine; D005998:Glycine