Effects of arginine infusion in infants: increased urea synthesis associated with unchanged ammonia blood levels.

Infusion of L-arginine hydrochloride in infants and children (ages ranging from 1 day to 12 yr) at a dosage of 0.5 g/kg body weight resulted in a dramatic increase in the arginine plasma concentration, with highest values of approximately 7 mmole/liter immediately after the end of the infusion; 120 min later the mean plasma level of the amino acid had decreased to mean values of 1 mmole/liter. These fluctuations were paralleled by increased ornithine concentrations, although the mean plasma levels of this amino acid remained far below those of arginine, i.e., 0.73 and 0.22 mmole/liter after 30 and 90 min, respectively. When expressed on a molar basis, arginine administration resulted in an almost stoichiometric rise in urinary urea excretion. These findings indicate that arginine is rapidly metabolized via urea and ornithine, the latter being transformed to glucose, as evidenced by a significant rise in the blood glucose concentration. Blood gas analyses and serum urea and blood ammonia concentrations determined after the load showed no significant deviations from preinfusion levels. Thus, in contrast to the effects to be expected form studies with tissue culture homogenates, even when administered to newborn infants, arginine does not impair the turnover of the urea cycle.