ROLE OF TRYPTOPHAN IN THE ELEVATED SEROTONIN-TURNOVER IN HEPATIC-ENCEPHALOPATHY

The increase of the brain levels of 5-hydroxyindoleacetic acid (5-HIAA ) in hepatic encephalopathy (HE) suggests an increased turnover of ser otonin (5-HT). To study the role of tryptophan on the increased brain 5-HT metabolism in HE, we attempted to monitor brain levels of tryptop han in rats with thioacetamide-induced acute liver failure by intraven ous infusion of branched-chain amino acids (BCAA). The effect of this treatment on 5-HT synthesis and metabolism was investigated in five br ain areas. BCAA-infusions (1 and 2 gm/kg/24 h) increased the ratio BCA A/aromatic amino acids in plasma two- and fourfold, respectively, and lowered both plasma and brain levels of tryptophan. At the higher BCAA -dose all parameters suggesting an altered brain 5-HT metabolism (incr eased brain levels of 5-HT and 5-HIAA, increased 5-HIAA/5-HT ratio) we re almost completely normalized. These results provide further evidenc e for the role of tryptophan in the elevation of brain 5-HT metabolism and for a potential role of BCAA in the treatment of HE.