Comparative effects of DL, D and L-3-pyridylalanine on serotonin concentration and tryptophan-serotonin metabolizing enzymes.

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Abstract
The administration of DL-3-pyridylalanine (DL-3-PA, DL-.alpha.-amino-3-pyridinepropanoic acid) or L-3-PA significantly increased brain serotonin (5-HT) concentration without affecting the other tissue 5-HT concentrations in male Wistar rats. The increase in brain 5-HT upon the administration of DL or L-3-PA was maintained for a long time (at least 96 h). DL and L-3-PA decreased tryptophan pyrrolase activity in the liver and increased free Trp concentration in the serum. These effects found in rats given a 100mg/kg dose of DL-3-PA were not statistically different from those in rats given a 50 mg/kg dose of L-3-PA. DL and L-3-PA hardly affected the activities of L-tryptophan 5-hydroxylase, 5-hydroxy-L-tryptophan decarboxylase and monoamine oxidase in the brain. D-3-PA had no effect on 5-HT concentration or tryptophan-5-HT metabolizing enzymes in rats. The action of DL-3-PA is apparently due to L-3-PA, not D-3-PA.