Differences in plasma L-glutamine (L-Gln) concentrations from ingestion of different formulations of L-Gln were examined in 8 men (26.8 ± 4.2 years old, 181.1 ± 10.9 cm, 85.8 ± 15.4 kg). Subjects reported to the laboratory on 4 separate occasions and randomly consumed 1 of 4 drinks containing 60 mg/kg of L-Gln; 89 mg/kg of Sustamine (L-alanylglutamine [AlaGln]; Kyowa Hakko Europe GmbH, Düsseldorf, Germany), which contained an equivalent L-Gln dose as consumed in L-Gln); 200 mg/kg of an enzymatically hydrolyzed wheat protein (HWP) with an L-Gln content of 31 mg/kg; or a control that consisted only of water. It was hypothesized that the AlaGln trial would increase plasma glutamine concentrations greater than the other experimental trials. Ingestion of L-Gln, AlaGln, and HWP resulted in significant increases in the plasma L-Gln concentration, peaking at 0.5, 0.5, and 0.75 hours, respectively. The corresponding mean peak increases were 179 ± 61, 284 ± 84, and 134 ± 36 μmol/L, respectively. Concentrations returned to baseline in all subjects by 2 hours after L-Gln and HWP and by 4 hours after AlaGln. Mean areas under the plasma concentration curve, calculated between 0 and 4 hours, were 127 ± 61, 284 ± 154, and 151 ± 63 μmol∙h∙L⁻¹ for L-Gln, AlaGln, and HWP, respectively. When allowance was made for the lower L-Gln dose administered as HWP, the peak plasma concentration and area under the plasma concentration curve were approximately the same as for AlaGln. The results suggest a greater transfer from the gut to plasma of L-Gln when supplied as AlaGln and possibly also as HWP compared with when the same dose was provided as the free amino acid.
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