Plasma glutamine response to enteral administration of glutamine in human volunteers (free glutamine versus protein-bound glutamine)

The goal of the present work was to compare the plasma glutamine response t o exogenous glutamine administration in human volunteers, glutamine was pro vided as a free amino acid, bound to proteins, or in the form of peptides. Plasma glutamine concentrations were measured in eight human volunteers at 30, 60, 90, 120, and 240 min after receiving a drink containing 30 g of pro tein from one of the five different proteins tested (sodium caseinate, sodi um caseinate + free glutamine, carob germ flour, carob protein concentrate, and carob protein hydrolysate). Peak plasma glutamine concentrations were 42% higher than postabsorptive basal. values when exogenous glutamine was a dministered in the form of free glutamine added to caseinate (925.9 +/- 67. 7 versus 651.3 +/- 41.0 mu mol/L, respectively). In contrast, when glutamin e was offered 100% bound to proteins (carob proteins), peak plasma glutamin e concentration increased only between 18% and 23% from basal values, possi bly because of the lower digestibility of carob proteins versus that of cas einate + free glutamine, to a different glutamine utilization at the gut le vel, or to a different response in endogenous glutamine kinetics to enteral administration of glutamine, depending on the molecular form of the glutam ine source (free or protein bound). (C)Elsevier Science Inc. 2000.