Differential metabolic fate of the carbon skeleton and amino-N of [13C]alanine and [15N]alanine ingested during prolonged exercise.
The decarboxylation/oxidation and the deamination of 13C- and [15N]alanine ingested (1 g/kg or 73.7 +/- 2 g) during prolonged exercise at low workload (180 min at 53 +/- 2% maximal O2 uptake) was measured in six healthy male subjects from V13CO2 at the mouth and [15N]urea excretion in urine and sweat. Over the exercise period, 50.6 +/- 3.5 g of exogenous alanine were oxidized (68.7 +/- 4.5% of the load), providing 10.0 +/- 0.6% of the energy yield vs. 4.8 +/- 0.4, 47.6 +/- 4.3, and 37.4 +/- 4.7% for endogenous proteins, glucose, and lipids, respectively. Alanine could have been oxidized after conversion into glucose in the liver and/or directly in peripheral tissues. In contrast, only 13.0 +/- 3.2 mmol of [(15)N]urea were excreted in urine and sweat (10.6 +/- 0.4 and 2.4 +/- 0.5 mmol, respectively), corresponding to the deamination of 2.3 +/- 0.3 g of exogenous alanine (3.1 +/- 0.4% of the load). These results confirm that the metabolic fate of the carbon skeleton and the amino-N moiety of exogenous alanine ingested during prolonged exercise at low workload are markedly different. The large positive nitrogen balance (8.5 +/- 0.3 g) suggests that in this situation protein synthesis could be increased when a large amount of a single amino acid is ingested.
Département de kinésiologie, Université de Montréal, Montréal H3C 3J7, Canada G9A 5H7.
M
M
Korach-André
Y
Y
Burelle
F
F
Péronnet
D
D
Massicotte
C
C
Lavoie
C
C
Hillaire-Marcel
D000328:Adult; D000409:Alanine / Q000378:metabolism*; D002153:Calorimetry, Indirect; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes; D004734:Energy Metabolism / Q000502:physiology*; D006801:Humans; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D005082:Physical Exertion / Q000502:physiology*; D014508:Urea / Q000652:urine
D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D002245:Carbon Dioxide; D002244:Carbon; D014508:Urea; D009584:Nitrogen; D000409:Alanine; D010100:Oxygen