PROTEIN-TURNOVER IN THE KIDNEY AND THE WHOLE-BODY IN HUMANS

For a better understanding of protein synthesis and degradation in the human kidney, the arteriovenous difference technique across the kidne y, splanchnic organs, and leg muscle was combined with labeled leucine and phenylalanine isotope dilution models. Results indicate that in t he postabsorptive state, the protein balance across the human kidney i s negative because the rate of leucine release from protein degradatio n is greater than the amount used for protein synthesis. In the splanc hnic bed, net protein balance is neutral since the amount of leucine d eriving from protein degradation is similar to the amount utilized for protein synthesis. In the leg muscle, protein degradation exceeds pro tein synthesis. The kidney exhibits the highest leucine metabolic acti vity when expressed in terms of total organ leucine content. The estim ated fractional protein synthesis rate in the human kidney is about 40 % per day (vs. about 2% in muscle and 12% in the splanchnic bed). The human kidney presents high rates of protein turnover and accounts for a significant fraction of whole-body protein degradation, protein synt hesis, and leucine oxidation.