Joaquin Cortiella, Julio Sérgio Marchini, S. Branch
Sep 1, 1992
Citations
1
Influential Citations
28
Citations
Quality indicators
Journal
The American journal of clinical nutrition
Abstract
Plasma phenylalanine (Phe) and tyrosine (Tyr) turnover and the rate of conversion of phenylalanine to tyrosine (Phehyd) and of phenylalanine oxidation (Pheox) after reduced intakes of Phe and Tyr were determined in a metabolic study involving five healthy young adult men. In a pilot study, six postabsorptive young men received either 12- or 4-h infusions of [2H2]Phe and [1-13C]Tyr or [1-13C]Phe and [2H2]Tyro. From these results a primed 8-h constant infusion of [1-13C]Phe and [2H2]Tyr and [2H3]leucine was used in the metabolic study (first 3 h fasted, the 5 h fed) at the end of 1-wk periods during which subjects received an adequate nitrogen L-amino acid based-diet followed by a restricted intake of Phe and Tyr. This procedure was again repeated after 1 and 3 wk when subjects were given a diet low in both nitrogen and Phe and Tyr. Phe and Tyr fluxes were not significantly affected by diet during the fasted metabolic state but Tyr fluxes were lower when the restricted intakes were given. Compared with the rate during the fasting state, Pheox was significantly higher (P less than 0.01) when the adequate diet was consumed; Pheox and Phehyd for fed and fasted states were similar when Phe and Tyr were restricted.