Effects of [15N]leucine infused at low rates on leucine metabolism in humans

Am J Physiol. 1985 Jul;249(1 Pt 1):E121-30. doi: 10.1152/ajpendo.1985.249.1.E121.


The present studies were carried out to determine whether infusions of [15N]leucine at low rates affect estimates of leucine oxidation and of proteolysis and protein synthesis in humans. Three groups of normal subjects were infused for 3 h with either [15N]leucine at a rate of 0.16 or 0.26 mumol X kg-1 X min-1 or saline using [2H3]leucine and alpha-[14C]ketoisocaproate as isotopic tracers of leucine metabolism. Data were analyzed at steady state using both single- and dual-isotope models. Preliminary studies were carried out to characterize the dual-isotope model in humans using infusions of [3H]leucine and alpha-[14C]ketoisocaproate. In the postabsorptive state estimates of leucine appearance, disappearance, and oxidation derived from the two isotope models were in good agreement. Infusion of stable isotope up to approximately 10% of the leucine carbon flux do not have a significant effect on leucine metabolism, but the data derived from such studies must be properly controlled and interpreted with care because these tracers are not massless.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Breath Tests
  • Carbon Radioisotopes
  • Deuterium
  • Female
  • Humans
  • Keto Acids / blood
  • Leucine / blood
  • Leucine / metabolism
  • Leucine / pharmacology*
  • Male
  • Models, Biological
  • Nitrogen Isotopes
  • Oxidation-Reduction
  • Proteins / metabolism*
  • Tritium


  • Carbon Radioisotopes
  • Keto Acids
  • Nitrogen Isotopes
  • Proteins
  • Tritium
  • alpha-ketoisocaproic acid
  • Deuterium
  • Leucine