An arginine-deficient diet in humans does not evoke hyperammonemia or orotic aciduria

The essentiality of dietary arginine was examined in adult humans with three biochemical indices: plasma levels of ammonium and amino acids and urinary orotic acid excretion. Three male and two female subjects participated in the 10-d study. Subjects consumed an L-amino acid diet containing 0.74 g protein equivalent/kg body weight on d 1-5; these amino acid concentrations were doubled on d 6-10. The diet was devoid of arginine on d 3-8. Daily urine was collected and blood samples were drawn on 6 of the 10 d at 0, 0.5, 1, 2, 3 and 4 h after the breakfast meal. When arginine was removed from the diet, urinary orotic acid did not increase, in contrast to what has been reported in most other animal species tested. Plasma ammonium concentrations remained within normal limits throughout the study. A small postprandial decrease in plasma arginine concentration was observed when the arginine-deficient diet was consumed; this decline disappeared when the diet was resupplied with arginine. The results of this study suggest that over the short term the adult human's capacity for de novo arginine synthesis when fed a dietary deficiency of arginine is sufficient for the maintenance of normal cellular metabolism.