Péronnet F, Massicotte D, Brisson G, Hillaire-Marcel C
Département d'Education Physique, Université de Montréal, Quebec, Canada.
J Appl Physiol (1985). 1990 Sep;69(3):1047-52. doi: 10.1152/jappl.1990.69.3.1047.
The purpose of this study is to outline a common mistake made when the rate of oxidation of exogenous substrates during prolonged exercise is computed using 13C naturally labeled substrates. The equation proposed and commonly used in the computation does not take into account that exercise and/or exogenous substrate ingestion modifies the composition of the mixture of endogenous substrates oxidized and, consequently, the isotopic composition of CO2 arising from oxidation of endogenous substrates. The recovery of 13C and the amount of exogenous substrate oxidized are thus overestimated. An adequate procedure for the computation of exogenous substrate oxidation taking into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates is suggested. Results from a pilot experiment (4 subjects) using this procedure indicate that over 2 h of exercise (66% of maximal O2 uptake), with ingestion of 60 g of glucose, 39 +/- 4 g of glucose were oxidized. Estimates made without taking into account changes in isotopic composition of CO2 arising from oxidation of endogenous substrates range between 70 +/- 8 and 44 +/- 3 g depending on 1) the isotopic composition of exogenous glucose and 2) the isotopic composition of expired CO2 taken as reference (rest or exercise without glucose ingestion). These observations suggest that results from previous studies of exogenous substrate oxidation during exercise using 13C labeling should be used with caution.
本研究的目的是概述在使用天然标记的13C底物计算长时间运动期间外源性底物氧化速率时所犯的一个常见错误。计算中提出并常用的公式没有考虑到运动和/或外源性底物摄入会改变内源性底物氧化混合物的组成，因此也没有考虑到内源性底物氧化产生的二氧化碳的同位素组成。因此，13C的回收率和外源性底物氧化量被高估。本文提出了一种适当的计算外源性底物氧化的方法，该方法考虑了内源性底物氧化产生的二氧化碳同位素组成的变化。使用该方法的一项初步实验（4名受试者）结果表明，在摄入60克葡萄糖并进行超过2小时的运动（最大摄氧量的66%）过程中，有39±4克葡萄糖被氧化。在不考虑内源性底物氧化产生的二氧化碳同位素组成变化的情况下进行的估算值在70±8克至44±3克之间，这取决于1）外源性葡萄糖的同位素组成和2）作为参考的呼出二氧化碳的同位素组成（静息状态或未摄入葡萄糖的运动状态）。这些观察结果表明，以往使用13C标记研究运动期间外源性底物氧化的研究结果应谨慎使用。
