Arginine-deficient diets alter plasma and tissue amino acids in young and aged rats

Blood and urine metabolites were measured in two experiments for young (2-mo-old) and aged (20-mo-old) male Sprague-Dawley rats fed arginine-devoid diets made isonitrogenous to a control 1.12% arginine diet by adding alanine or glycine. Diet, fed for 7 or 13 d, had little effect on urinary or plasma ammonia and urea. Urinary orotate excretion was more than 40-fold higher in rats fed the arginine-deficient diets (P less than 0.01) in both experiments. Source of nonessential N (alanine or glycine) in the arginine-deficient diets did not alter orotic acid excretion or plasma or urine ammonia or urea. Changes in plasma arginine, alanine and glycine concentrations reflected the levels of these amino acids in the diet. Tissue ornithine levels reflected dietary arginine level, but tissue citrulline was unaffected by dietary arginine. Glutamate and glutamine were greater in the plasma and liver of rats fed arginine-deficient diets. Plasma concentrations of glutamate and glutamine were positively correlated with urinary orotic acid excretion (P less than 0.05) and ornithine and arginine were negatively correlated with orotic acid excretion (P less than 0.01). Increased tissue glutamine may be related to the greater orotate excretion in rats fed arginine-devoid diets. The metabolic responses to dietary arginine deficiency were similar in young and aged rats. In general, concentrations of amino acids in plasma, liver and spleen were higher in aged rats.