Inhibition of serotonin biosynthesis by 6-halotryptophans in vivo

The 6-halotryptophans, which had previously been shown to inhibit tryptophan hydroxylase in brain, were examined further for in vivo inhibition both in brain and in peripheral tissues. Serotonin, tryptophan hydroxylase and 5-hydroxyindoleacetic acid levels in brain and serotonin levels in other tissues were substantially lowered after intraperitoneal injection of dl-6-fluorotryptophan without significantly changing levels of the catecholamines or the activities of several of the enzymes involved in their biosynthesis and metabolism. The inhibitors freely entered the brain and were rapidly and completely excreted.