Effects of leucine on whole body leucine, valine, and threonine metabolism in humans
Hoffer, L.J.; Taveroff, A.; Robitaille, L.; Hamadeh, M.J.; Mamer, O.A.
American Journal of Physiology 272(6 Pt 1): E1037-E1042
1997
ISSN/ISBN: 0002-9513 PMID: 9227449 Document Number: 482610
We tested whether expansion of the plasma leucine pool distorts leucine or valine tracer kinetics, causing errors in the derived values of whole body proteolysis. Seven normal adults received a 10-h primed-continuous tracer infusion of L-(5,5,5-2H-3)leucine, L-(1-13C)valine, and L-(1-13C)threonine, during the final 7 h of which L-leucine was infused at a rate that more than tripled the plasma leucine concentration. Leucine, valine, and threonine rates of appearance were converted to a common value of whole body proteolysis on the basis of their concentrations in body proteins. The conversion of labeled leucine and valine to their corresponding branched-chain alpha-keto and alpha-hydroxy acids was also monitored. Before the unlabeled leucine infusion, postabsorptive whole body proteolysis was estimated similarly by the three tracers ( apprx 160 mg protein cntdot kg-1 cntdot h-1). The leucine infusion reduced proteolysis by an average of 21% (P lt 0.006), as estimated by use of valine or threonine kinetics, and by 10% by use of leucine kinetics (P lt 0.02). No delay in the conversion of valine to alpha-ketoisovalerate occurred during the leucine infusion. Thus all three tracers indicated similar postabsorptive rates of whole body proteolysis and a reduction of proteolysis during leucine administration, although the magnitude of the effect was underestimated with use of the leucine tracer.