Measurement of exogenous carbohydrate oxidation : a comparison of [U-14C]glucose and [U-13C]glucose tracers

The purpose of this study was to assess the level of agreement between two techniques commonly used to measure exogenous carbohydrate oxidation (CHOEXO). To accomplish this, seven healthy male subjects (24 +/- 3 yr, 74.8 +/- 2.1 kg, O2max 62 +/- 4 ml x kg-1 x min-1) exercised at 50% of their peak po...

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Bibliographic Details
Published in:American journal of physiology: endocrinology and metabolism 2005-08, Vol.52 (2), p.206-211
Main Authors: MOSELEY, L, JENTJENS, R. L. P. G, WARING, R. H, HARRIS, R. M, HARDING, L. K, JEUKENDRUP, A. E
Format: Article
Language:English
Subjects:
Biological and medical sciences
Carbohydrates
Comparative analysis
Fundamental and applied biological sciences. Psychology
Glucose
Oxidation
Vertebrates: endocrinology
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Summary:The purpose of this study was to assess the level of agreement between two techniques commonly used to measure exogenous carbohydrate oxidation (CHOEXO). To accomplish this, seven healthy male subjects (24 +/- 3 yr, 74.8 +/- 2.1 kg, O2max 62 +/- 4 ml x kg-1 x min-1) exercised at 50% of their peak power for 120 min on two occasions. During these exercise bouts, subjects ingested a solution containing either 144 g glucose (8.7% wt/vol glucose) or water. The glucose solution contained trace amounts of both [U-13C]glucose and [U-14C]glucose to allow CHOEXO to be quantified simultaneously. The water trial was used to correct for background 13C enrichment. 13C appearance in the expired air was measured using isotope ratio mass spectrometry, whereas 14C appearance was quantified by trapping expired CO2 in solution (using hyamine hydroxide) and adding a scintillator before counting radioactivity. CHOEXO measured with [13C]glucose ([13C]CHOEXO) was significantly greater than CHOEXO measured with [14C]glucose ([14C]CHOEXO) from 30 to 120 min. There was a 15 +/- 4% difference between [13C]CHOEXO and [14C]CHOEXO such that the absolute difference increased with the magnitude of CHOEXO. Further investigations suggest that the difference is not because of losses of CO2 from the trapping solution before counting or an underestimation of the "strength" of the trapping solution. Previous research suggests that the degree of isotopic fractionation is small (S. C. Kalhan, S. M. Savin, and P. A. Adam. J Lab Clin Med89: 285-294, 1977). Therefore, the explanation for the discrepancy in calculated CHOEXO remains to be fully understood. [PUBLICATION ABSTRACT]
ISSN:0193-1849
1522-1555