Relationships between tryptophan in serum and CSF, and 5-hydroxyindoleacetic acid in CSF of man: effect of cirrhosis of liver and probenecid administration.

Tryptophan was measured in the lumbar CSF and serum of patients undergoing neurological investigation (controls) and in patients with hepatic cirrhosis. Samples were taken from the fasting patients at 8:00 a.m. Under these conditions, in the controls the mean CSF, free )mpm-albumin-bound) and total serum tryptophan were in the approximate ratio 1:4:24. In this cross-sectional study, for the controls, CSF tryptophan was correlated significantly and positively with the total serum but not with the free serum tryptophan. In patients with advanced hepatic cirrhosis the mean CSF tryptophan concentration was greatly elevated. However, the mean total serum tryptophan was unchanged and the free serum tryptophan only slightly elevated. Administration of probenecid, which displaces tryptophan from binding sites on serum albumin, and thereby increases the proportion of serum tryptophan in the free form, did not affect CSF tryptophan.