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Relationships between plasma isotope enrichments of leucine and α‐ketoisocaproic acid during continuous infusion of labelled leucine
Author(s) -
THOMPSON G. N.,
PACY P. J.,
FORD G. C.,
MERRITT H.,
HALLIDAY D.
Publication year - 1988
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.1365-2362.1988.tb01280.x
Subject(s) - leucine , transamination , chemistry , medicine , bolus (digestion) , endocrinology , amino acid , biochemistry , biology
. The ratio at steady‐state of α‐ketoisocaproic acid (KIC) to leucine 13 C enrichments in plasma during continuous infusion of [ 13 C]leucine was examined in 58 studies under a variety of conditions. The ratio was lower ( P < 0·001) in ‘arterialized’ venous plasma (mean±SD 0·85±0·09) than in deep venous plasma (0·95±0·08), the sampling site enrichment differences being greater for leucine than for KIC. Variation in the ratio between the various conditions studied was largely explained by analytical variation. Three normal subjects were given an intravenous bolus dose of L‐[1‐ 13 C, 15 N]leucine. Both [ 13 C]KIC and [ 13 C]leucine appeared quantitatively in plasma within 10 min, indicating that both transamination of leucine and KIC, and their equilibration between intracellular fluid and plasma, is rapid. This study suggests that changes in sampling site, rather than in study conditions, are more likely to lead to variation in the KIC: leucine enrichment ratio. The lesser variation for KIC, and the rapid equilibration of the [ 13 C]leucine bolus, favour KIC as tracee for [ 13 C]leucine protein turnover studies.