title: Effects of leucine on whole body leucine, valine, and threonine metabolism in humans.
abstract: 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-[5,5,5-2H3]leucine, L-[(1-13)C]valine, and L-[(1-13)C]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 (approximately 180 mg protein.kg-1.h-1. The leucine infusion reduced proteolysis by an average of 21% (P < 0.006), as estimated by use of valine or threonine kinetics, and by 10% by use of leucine kinetics (P < 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.
authors.affiliation: McGill Nutrition and Food Science Centre, McGill Medical Research Council of Canada, McGill University, Montreal, Quebec, Canada.
authors.forename: L J
authors.initials: LJ
authors.lastname: Hoffer
authors.forename: A
authors.initials: A
authors.lastname: Taveroff
authors.forename: L
authors.initials: L
authors.lastname: Robitaille
authors.forename: M J
authors.initials: MJ
authors.lastname: Hamadeh
authors.forename: O A
authors.initials: OA
authors.lastname: Mamer
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000097:blood; D001711:Biotransformation; D002247:Carbon Isotopes; D003903:Deuterium; D005260:Female; D045782:Hemiterpenes; D006801:Humans; D007651:Keto Acids / Q000097:blood; D007700:Kinetics; D007930:Leucine / Q000378:metabolism* / Q000494:pharmacology*; D008297:Male; D011865:Radioisotope Dilution Technique; D013912:Threonine / Q000378:metabolism*; D013997:Time Factors; D014633:Valine / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D045782:Hemiterpenes; D007651:Keto Acids; D013912:Threonine; C001505:alpha-ketoisovalerate; C013082:alpha-ketoisocaproic acid; D003903:Deuterium; D007930:Leucine; D014633:Valine