Contribution of plasma proteins to splanchnic and total anabolic utilization of dietary nitrogen in humans

Splanchnic tissues are largely involved in the postprandial utilization of dietary amino acids, but little is yet known, particularly in humans, about the relative contributions of different splanchnic protein pools to splanchnic and total postprandial anabolism. Our aim was to develop a compartmental model that could distinguish dietary nitrogen (N) incorporation among splanchnic constitutive, plasma (splanchnic exported), and peripheral proteins after a mixed-protein meal in humans. Eight healthy subjects were fed a single mixed meal containing 15N-labeled soy protein, and dietary N postprandial kinetics were measured in plasma free amino acids, proteins, and urea and urinary urea and ammonia. These experimental data and others previously obtained for dietary N kinetics in ileal effluents under similar experimental conditions were used to develop the compartmental model. Six hours after the mixed-meal ingestion, 31.5, 7.5, and 21% of ingested N were predicted to be incorporated into splanchnic constitutive, splanchnic exported, and peripheral proteins, respectively. The contribution of splanchnic exported proteins to total splanchnic anabolism from dietary N was predicted to be approximately 19% and to remain steady throughout the simulation period. Model behavior and its predictions were strongly in line with current knowledge of the system and the scarce, specific data available in the literature. This model provides the first data concerning the anabolism of splanchnic constitutive proteins in the nonsteady postprandial state in humans. By use of only slightly invasive techniques, this model could help to assess how the splanchnic anabolism is modulated under different nutritional or pathophysiological conditions in humans.