Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise.
In this study, five men exercised the knee extensor muscles of one leg for 60 min (71 +/- 2% maximal work capacity) with and without (control) an oral supplement (77 mg/kg) of branched-chain amino acids (BCAA). BCAA supplementation resulted in a doubling (P < 0.05) of the arterial BCAA levels before exercise (339 +/- 15 vs. 822 +/- 86 microM). During the 60 min of exercise, the total release of BCAA was 68 +/- 93 vs. 816 +/- 198 mumol/kg (P < 0.05) for the BCAA and control trials, respectively. The intramuscular BCAA concentrations were higher (P < 0.05) for the BCAA trial and remained higher (P < 0.05) throughout exercise. In both trials, substantial quantities of NH3 were released, and when NH3 production equivalent to IMP accumulation was subtracted the net NH3 production was 1,112 +/- 279 and 1,670 +/- 245 mumol/kg (P < 0.05) for the control and BCAA trials, respectively. In contrast, the release of the essential amino acids (EAA) was much lower for the BCAA than the control trial (P < 0.05). When the BCAA were subtracted from the EAA (EAA-BCAA), the total release of EAA minus BCAA was lower (P < 0.05) for the BCAA (531 +/- 70 mumol/kg) than the control (924 +/- 148 mumol/kg) trial. These data suggest that BCAA supplementation results in significantly greater muscle NH3 production during exercise. Furthermore, the increased intramuscular and arterial BCAA levels before and during exercise result in a suppression of endogenous muscle protein breakdown during exercise.
MacLean
D A
DA
School of Human Biology, University of Guelph, Ontario, Canada.
Graham
T E
TE
Saltin
B
B
D000293:Adolescent; D000328:Adult; D000597:Amino Acids, Branched-Chain / Q000494:pharmacology*; D000641:Ammonia / Q000378:metabolism*; D015444:Exercise; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D006801:Humans; D007291:Inosine Monophosphate / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000378:metabolism; D010101:Oxygen Consumption; D011506:Proteins / Q000378:metabolism*
D000597:Amino Acids, Branched-Chain; D005230:Fatty Acids, Nonesterified; D011506:Proteins; D007291:Inosine Monophosphate; D000641:Ammonia