Labeled CO(2) production and oxidative vs nonoxidative disposal of labeled carbohydrate administered at rest.
Carbon isotopes (*C) have been extensively used in man to describe oxidative vs nonoxidative disposal of an exogenous load of labeled carbohydrate (*C-CHO) at rest in various experimental situations. It is hypothesized that V*CO(2) reflects *C-CHO oxidation. However, when glycogen is synthesized through the indirect pathway (which is responsible for approximately 50% of glycogen storage), *C could be lost, diluted, and exchanged in the pyruvate-lactate pool, in the pool of tricarboxylic acid cycle intermediates, as well as at the entrance of the tricarboxylic acid cycle, and along the pathway of gluconeogenesis. This could result in a lower *C/C in the glycogen stored than in the CHO administered, in an increased production of *CO(2), and, respectively, in an overestimation and an underestimation of the oxidative and nonoxidative disposal of the CHO load. Results from the present experiment offer a support to this hypothesis. Over a 10-hour period after ingestion of a (13)C-pasta meal (313+/-10 g dry mass or 258+/-8 g of glucose) in 12 healthy subjects (6 men and 6 women), exogenous CHO oxidation computed from V(13)CO(2) (recovery factor, 0.54) significantly exceeded total CHO oxidation computed by indirect respiratory calorimetry corrected for urea excretion: 154.2+/-2.6 vs 133.5+/-3.2 g. In an additional study conducted in rats, (13)C/(12)C in glycogen stores was significantly approximately 50% lower than in the (13)C-CHO ingested, over a wide range of enrichment. These results suggest that because of dilution, loss, and exchange of *C in the indirect pathway of glycogen synthesis, the oxidative vs nonoxidative disposal of exogenous *C-CHO cannot be accurately tracked from V*CO(2).
Folch
Nathalie
N
Département de kinésiologie, Université de Montréal, Montréal, Québec, Canada H3C 3J7.
Péronnet
François
F
Péan
Michel
M
Massicotte
Denis
D
Lavoie
Carole
C
D000328:Adult; D000818:Animals; D002153:Calorimetry, Indirect / Q000379:methods*; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D002952:Citric Acid Cycle / Q000502:physiology; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005260:Female; D005943:Gluconeogenesis / Q000502:physiology; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology; D019289:Pyruvic Acid / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012146:Rest / Q000502:physiology*; D014508:Urea / Q000652:urine
D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D004040:Dietary Carbohydrates; D002245:Carbon Dioxide; D019344:Lactic Acid; D019289:Pyruvic Acid; D014508:Urea; D006003:Glycogen