Absorption of enterally administered N-acetyl-l-glutamine versus glutamine in pigs

Background & aims: Glutamine instability in liquid media suggests that evaluation of reasonable enteral nutrition sources of glutamine is needed. N-acetyl-l-glutamine offers no instability and no intolerance problems. This research was conducted to study the absorption and apparent digestibility of glutamine versus N-acetyl-l-glutamine. Methods: Two pig models were used. (1) In a clamped jejunal loop experiment, we measured the concentrations of glutamine and N-acetyl-l-glutamine in the intestinal infused solutions, intestinal mucosa, and portal and peripheral blood. (2) In a feeding experiment, we determined their apparent digestibility. Results: N-acetyl-l-glutamine (∼76%) was slightly less absorbed than glutamine (∼85%) from the intestinal lumen into mucosa, where it was not detected as intact molecule, suggesting almost complete hydrolysis during absorption. Virtually no intact N-acetyl-l-glutamine was observed in the blood compartments; glutamine from lumenal N-acetyl-l-glutamine had the same behavior as that from lumenal-free glutamine in portal and peripheral blood. The apparent ileal digestibility of N-acetyl-l-glutamine was lower than that of free glutamine, as N-acetyl-l-glutamine was probably retained in the intestinal lumen to a greater extent than glutamine. Conclusion: N-acetyl-l-glutamine appeared to be a good candidate for glutamine fortification of enteral nutrition formulas.