Parenteral arginine infusion in humans: nutrient substrate or pharmacologic agent?

When given as a dietary supplement, arginine enhances lymphocyte mitogenesis and improves nitrogen balance. The purpose of this study was to evaluate arginine's ability to mediate these same effects when given as the sole nitrogen source with minimum additional calories. Thirty patients were randomized to receive 20 g/day arginine hydrochloride or a mixed amino acid solution (Travasol) by intravenous infusion for 7 days after abdominal operations. Mean patient age, body weight, gender ratios, and preoperative degree of weight loss were similar between groups. Mean plasma arginine and ornithine levels rose to 228 +/- 50 mumol/L and 191 +/- 76 mumol/L in the arginine group during infusion. Mean nitrogen balance was -8.8 g/day and -9.2 g/day in the arginine and Travasol groups, respectively. Mean lymphocyte stimulation indices to concanavalin A and phytohemagglutinin fell on postoperative day 1 in both groups. No significant differences in patterns of lymphocyte mitogenesis changes were noted between groups. The mean total number of circulating T cells increased in the arginine group at postoperative day 7. Thus, parenteral arginine infusion in postoperative patients provided comparable nitrogen balance to a balanced amino acid solution but did not increase peripheral blood lymphocyte mitogenesis. When arginine is given parenterally as the sole nitrogen source with minimal additional calories to postoperative patients, no enhancement of mitogen-stimulated lymphocyte proliferation could be demonstrated.