Glutamate ingestion and its effects at rest and during exercise in humans

Glutamate is central to several transamination reactions that affect the production of ammonia, alanine, glutamine, as well as TCA cycle intermediates during exercise. To further study glutamate metabolism, we administered 150 mg/kg body wt of monosodium glutamate (MSG) and placebo to seven male subjects who then either rested or exercised (15-min cycling at approximately 85% maximal oxygen consumption). MSG ingestion resulted in elevated plasma glutamate, aspartate, and taurine, both at rest and during exercise (P < 0.05), whereas most other amino acids were unchanged. Neither plasma alanine nor ammonia was altered at rest. During exercise and after glutamate ingestion, alanine was increased (P < 0.05) and ammonia was attenuated (P < 0.05). Glutamine was also elevated after glutamate ingestion during rest and exercise trials. MSG administration also resulted in elevated insulin levels (P < 0.05), which were parallel to the trend in C-peptide levels. Thus MSG can successfully elevate plasma glutamate, both at rest and during exercise. The plasma amino acid responses suggest that increased glutamate availability during exercise alters its distribution in transamination reactions within active muscle, which results in elevated alanine and decreased ammonia levels.