Mechanisms of elevation of rat brain tryptophan concentration by various doses of salicylate.

1 The roles of inhibition of liver tryptophan pyrrolase activity and of displacement of tryptophan from its binding sites on serum proteins have been investigated in relation to the increase in rat brain tryptophan concentration after administration of various doses of sodium salicylate. 2 The elevation of brain tryptophan concentration by sodium salicylate (0.5 mg/kg) was caused by inhibition of liver pyrrolase activity, whereas that by doses of the drug of 50 mg/kg and above was achieved mainly by tryptophan displacement. Both tryptophan displacement of pyrrolase inhibition caused the increase in brain tryptophan concentration by sodium salicylate at 10 mg/kg. 3 The smallest dose of salicylate capable of displacing serum-protein-bound tryptophan was 2.5 mg/kg.