Impact of oral L-glutamine on glutathione, glutamine, and glutamate blood levels in volunteers

OBJECTIVE: We investigated the effect of glutamine supplementation on plasma glutamine (Gln), glutamate (Glu), and whole-blood glutathione (GSH) concentrations in human volunteers. METHODS: Subjects first adapted to a standard diet with known intakes of protein. total GSH. cysteine, methionine, and total Glu (Glu values include Glu and Gln) for 3 d. Plasma Gln, Glu. and whole-blood GSH levels were then measured at 4-h intervals over 24 h. Supplemental oral Gln (0.3 g (.) kg(-1) (.) d(-1)) was ingested for 10 d and then 24-h plasma levels of Gln, Glu, and whole-blood GSH were measured, RESULTS: The plasma concentrations of Glu (116%; P = 0.006) and Gln (20%: P = 0.046) were significantly higher, whereas concentrations of GSH were significantly lower (37%: P = 0.00091) after oral Gln supplementation. CONCLUSION: Oral Gln increases Glu and Gln levels in plasma of healthy subjects but does not increase GSH red cell (whole-blood) levels. Thus, GSH biosynthesis and preservation of GHS stores in red blood eel Is may involve rate-limiting substrates other than Gln. (C)Elsevier Science Inc. 2002.