Local and systemic effects of phenylalanine on intestinal transport of tyrosine and tryptophan.

SummaryThe local and the systemic effects of Phe on the intestinal transport of 1 mM Tyr and 5 mM Trp in Krebs-Henseleit buffers were studied in vitro by everted rat intestinal loops and in vivo by perfusion. The presence of equimolar Phe in the buffer did not inhibit the transport of Tyr and Trp in the in vitro everted intestinal loops, or in the in vivo perfusion studies. However, there was a significant inhibition in the in vitro and in the in vivo experiments (36 and 37%, respectively) when Phe was present in the buffers in a 10:1 ratio. Hyperphenylalanine-mia did not alter amino acid absorption. There were no differences in the transport of Tyr and Trp both in vitro and in vivo between the intestinal loop preparations of rats fed diets containing either 1.2, 8.2 or 0.1% Phe and 0.1% pCPA.