Metabolism of compounds labeled with ¹⁵N by an infant with congenital hyperammonemia

The excretion of¹⁵N in the urine following the oral administration of compounds labeled with¹⁵N was evaluated in an infant with congenital hyperammonemia while the infant was receiving a low protein diet. When she received either¹⁵N-glycine or¹⁵NH₄C1, the ratio of [¹⁵N-NH₃] to [¹⁵N-urea] in urine was strikingly elevated with respect to [¹⁵N-NH₃] [¹⁵N-urea] found in studies of other infants receiving high protein diets. However, reduction of the protein in the diet of the control infants resulted in elevation of the ratio of [¹⁵N-NH₃] to [¹⁵N-urea] in urine after the administration of¹⁵N-glycine or¹⁵NH₄C1. No mode of metabolism specific for congenital hyperammonemia was demonstrated in the studies of orally administered¹⁵NH₄C1. In the metabolism of¹⁵N-glycine, the hyperammonemic infant receiving a low protein diet was different from other infants on both high and low protein diets. In the hyperammonemic infant, lsN-urea was much more readily formed from¹⁵N-citrulline than from¹⁵NH₄C1. On the other hand, the addition of unlabeled citrulline to the diet of this infant did not enhance the synthesis of¹⁵N-ureafrom ingested¹⁵NH₄C1 when compared with the addition of unlabeled ornithine-HGl to the diet.