QUANTIFICATION OF INCORPORATION OF [N-15]AMMONIA INTO PLASMA AMINO-ACIDS AND UREA

The incorporation of N-15 into individual plasma amino acids and urea was quantified in five human subjects who received (NH4Cl)-N-15 either orally or intravenously for 6 h. After oral tracer administration, th e highest enrichment was achieved by arginine, followed by urea and gl utamine; distribution of N-15 within glutamine was 55% amide and 45% a mino N. Glutamine achieved the highest enrichment after the intravenou s administration of tracer, with a distribution of 92% amide and 8% am ino N. The relative distribution pattern of N-15 incorporation was qua ntified from the rate at which N-15 initially appeared in each plasma component. Amino acids (especially arginine, glutamine, and glutamate) accounted for greater than one-half (54%) of the orally administered tracer that was initially recovered in plasma components, compared wit h 46% initial appearance for urea; for the intravenous tracer, amino a cids accounted for 78% of initial appearance of tracer compared with 2 2% for urea. Our results highlight the involvement of the splanchnic b ed in the utilization of orally administered ammonia (preferential inc orporation of oral tracer into arginine, urea, glutamate, and the amin o N of glutamine) in contrast to the preferential incorporation of sys temically administered ammonia into the amide N of glutamine and alani ne.