Equilibration of 15N-labeled amino compounds in man
Stein, T.P.; Leskiw, M.J.; Wallace, H.W.
American Journal of Physiology 230(5): 1326-1330
1976
ISSN/ISBN: 0002-9513 PMID: 1275074 Document Number: 105780
After overnight fasting, volunteers were given 15N-labelled glycine, ammonium chloride or aspartic acid by mouth, in hourly aliquots for 12 h, or as a continuous infusion into a peripheral vein for 10 to 12 h, and all took sodium benzoate 500 mg/h during administration of 15N. Venous blood and urine samples were taken serially. Specific activity curves for urinary ammonia, urinary hippuric acid and plasma amino acids after administration of each of the 3 carriers by either route reached a plateau after 6 to 10 h. When [15N]glycine was used, the specific activity of hippuric acid was greater than with the other carriers and it rose further when glycine was given orally. Urinary ammonia labelling was greatest when NH4Cl was given by vein. No significant delay in appearance of 15N in urinary urea was found when glycine was the source, but urinary urea increased with time in all cases. It is concluded that an isotopic steady state is reached 6 to 10 h after giving [15N]amino acid and that mixing of the labelled amino acids is probably the rate-controlling step.