15N-Studies in Severe Renal Failure I. Influence of Amino Acid Administration on the Nitrogen Metabolism

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Abstract
15N-urea was administered to two uraemic patients and to one normal subject treated with intravenous infusions of the 8 essential amino acids supplemented with histidine and arginine. The 15N in plasma and muscle protein and in non-protein nitrogen was compared to the nitrogen balance and plasma urea concentration. Before the infusions the nitrogen balance was negative and incorporation of 15N in the proteins decreasing, whereas incorporation in tissue NPN was almost stable. When amino acids were infused, the protein incorporation first increased and then remained almost constant in one patient and decreased slowly in the other, concomitantly with a decreased 15N-content in the tissue NPN. The healthy subject quickly lost most of the 15N in the urine and the 15N-incorporation in protein and NPN was low. The results demonstrate that urea nitrogen can be utilized for synthesis of muscle protein in uraemic patients. Administration of essential amino acids seemed to stimulate utilization of nitrogen-containing metabolites for protein synthesis.