EFFECTS OF CHRONIC PORTO‐CAVAL ANASTOMOSIS ON BRAIN TRYPTOPHAN, TYROSINE AND 5‐HYDROXYTRYPTAMINE

Abstract

Abstract —Three weeks after porto‐caval anastomosis, tryptophan and 5‐hydroxyindolylacetic acid concentrations were‐greatly increased in rat brain regions. 5‐Hydroxytryptamine showed smaller increases. Midbrain tyrosine and muscle tyrosine and tryptophan concentrations were also increased. Striatal dopa‐mine concentration was not significantly changed. Unlike previous results from acute liver failure, brain tryptophan changes in this chronic study did not simply reflect plasma‐free tryptophan changes. Midbrain tryptophan/plasma‐free tryptophan ratio and midbrain tyrosine/plasma tyrosine ratio both rose, suggesting increased effectiveness of uptake of these amino acids from plasma by brain. Corresponding muscle/plasma ratios were unaltered by the porto‐caval anastomosis. Uptake of tryptophan from buffer by cerebral cortex slices was unaffected. Results on control animals illustrate the importance of plasma‐free tryptophan in the normal physiological control of brain tryptophan.