Metabolic effects of arginine addition to the enteral feeding of critically Ill patients

Background. Some studies have suggested that the addition of arginine to en teral feeding solutions may improve outcome in critically ill patients, but the mechanism is incompletely explained. In particular, the availability a nd utilization of arginine administered enterally is not wen defined. Metho ds: This prospective, randomized, double-blind, placebo-controlled study pe rformed in a Department of Medicosurgical Intensive Care included 51 patien ts likely requiring long-term enteral feeding. Thirty-seven patients (57 +/ - 7 years, SAPS II 33 +/- 6) completed the 7-day study, of whom 20 received the formula enriched with free arginine (6.3 g/L) and 17 received an isoca loric and isonitrogenous control solution. Arginine absorption was assessed from plasma arginine concentrations in serial samples. Three pathways of a rginine utilization were explored: (1) the production of nitric oxide, asse ssed by the plasma concentration of nitrite/nitrate (NOx) and citrulline, a nd 24-hour urinary excretion of NOx; (2) the protein turnover, estimated by the phenylalanine concentrations; and (3) the activity of arginase, reflec ted by the ornithine concentration. Results: The plasma concentrations of a rginine and ornithine increased in the group fed with the enriched formula (from 55 +/- 9 mu mol/L to 102 +/- 9 mu mol/L and from 57 +/- 7 to 135 +/- 11 mu mol/L, respectively, p < .05), but not with the control formula. Ther e was no difference between groups in either NO production or phenylalanine concentration. Conclusions: Supplemental arginine in enteral feeding is re adily absorbed, and mainly metabolized into ornithine, presumably by the ar ginase enzyme.