Premium
Direct determination of leucine metabolism and protein breakdown in humans using L‐[1‐ 13 C, 15 N]‐leucine and the forearm model
Author(s) -
CHENG K. N.,
DWORZAK F.,
FORD G. C.,
RENNIE M. J.,
HALLIDAY D.
Publication year - 1985
Publication title -
european journal of clinical investigation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.164
H-Index - 107
eISSN - 1365-2362
pISSN - 0014-2972
DOI - 10.1111/j.1365-2362.1985.tb00283.x
Subject(s) - leucine , chemistry , forearm , isotope , metabolism , venous blood , blood flow , deamination , chromatography , medicine , endocrinology , nuclear medicine , biochemistry , amino acid , enzyme , anatomy , quantum mechanics , physics
. We have used the forearm model to study protein metabolism in six normal healthy subjects in the fed state using L‐[1 – 13 C, 15 N]‐leucine as the substrate tracer. Deep venous and arterialized venous blood samples from the forearm were collected at 10‐min intervals 2±5 h into a primed‐continuous infusion of the dilabelled tracer. Arterialized venous blood was obtained using a ‘hot‐box’ technique and forearm blood flow was measured by mercury strain‐gauge plethysmography. The concentration and isotope enrichment of leucine and its metabolites, α‐ketoisocaproic acid and CO 2 , in deep venous and arterialized venous blood were measured by gas chromatography‐mass spectrometry and isotope ratio‐mass spectrometry. The rates of leucine deamination and reamination were 388 ± 24 (mean ± SEM) and 330 ± 23 nmol (100 ml) ‐1 min ‐1 respectively, whilst protein synthesis and breakdown rates were 127 ± 11 and 87 ± 10 nmol (100 ml) ‐1 min ‐1 respectively across the forearm in the fed state. We have demonstrated that the use of doubly labelled leucine as tracer and application of the mathematical model developed in this study, permits the comprehensive quantification of leucine kinetics including protein breakdown.