Recycling of an amino acid label with prolonged isotope infusion: implications for kinetic studies

W Frederick Schwenk; Eva Tsalikian; Bernard Beaufrere; Morey W Haymond

doi:10.1152/ajpendo.1985.248.4.E482

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Recycling of an amino acid label with prolonged isotope infusion: implications for kinetic studies

Journal article

Peer reviewed

Recycling of an amino acid label with prolonged isotope infusion: implications for kinetic studies

W Frederick Schwenk, Eva Tsalikian, Bernard Beaufrere and Morey W Haymond

The American journal of physiology, Vol.248(4 Pt 1), pp.E482-487

04/1985

DOI: 10.1152/ajpendo.1985.248.4.E482

PMID: 3985146

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Abstract

To investigate whether recycling of a labeled amino acid would occur after 24 h of infusion, two groups of normal volunteers were infused with [3H]leucine and alpha-[14C]-ketoisocaproate for 4 h and [2H3]leucine for either 4 or 24 h (groups I and II, respectively). Entry of [2H3 )leucine at steady state into the plasma space was indistinguishable from its infusion rate for group I but 30% higher (P less than 0.001) than this rate for group II, demonstrating significant recycling of label. After discontinuation of the infusions, isotope disappearance from the plasma space was followed for 2 h. The 3H and 14C decay data for both groups suggest that plasma leucine and alpha-ketoisocaproate are derived from a single intracellular pool in the postabsorptive state. In group I, the 3H and 2H labels decayed identically; whereas, in group II, the decay of [2H3]-leucine and alpha-[2H3]ketoisocaproate was slower (P less than 0.01) than the decay of [3H]leucine and alpha-[3H]ketoisocaproate, confirming re-entry of label after a 24-h infusion. Therefore kinetic values calculated from models assuming no recycling of labeled amino acids are most likely not quantitative and must be interpreted with care when flux does not change or decreases.

Leucine - metabolism

Time Factors

Humans

Adult

Female

Male

Tritium

Kinetics

Caproates - metabolism

Keto Acids - metabolism

Carbon Radioisotopes

Details

Title: Subtitle: Recycling of an amino acid label with prolonged isotope infusion: implications for kinetic studies
Creators: W Frederick Schwenk
Eva Tsalikian
Bernard Beaufrere
Morey W Haymond
Resource Type: Journal article
Publication Details: The American journal of physiology, Vol.248(4 Pt 1), pp.E482-487
DOI: 10.1152/ajpendo.1985.248.4.E482
PMID: 3985146
ISSN: 0002-9513
eISSN: 2163-5773
Grant note: AM-26989 / NIADDK NIH HHS RR585 / NCRR NIH HHS AM-07352 / NIADDK NIH HHS
Language: English
Date published: 04/1985
Academic Unit: Stead Family Department of Pediatrics; Fraternal Order of Eagles Diabetes Research Center
Record Identifier: 9984093325202771

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