Effect of combined administration of tryptophan with putative tryptophan pyrrolase inhibitors, DL-3-pyridylalanine, allopurinol or nicotinamide, on brain serotonin concentration.

@article{Shimeno1984EffectOC,
  title={Effect of combined administration of tryptophan with putative tryptophan pyrrolase inhibitors, DL-3-pyridylalanine, allopurinol or nicotinamide, on brain serotonin concentration.},
  author={Hiroshi Shimeno and Y Fukumoto and M Fuji and Atsuo Nagamatsu},
  journal={Chemical \& pharmaceutical bulletin},
  year={1984},
  volume={32 6},
  pages={
          2353-63
        }
}
1) Single administration of tryptophan (25-200 mg / kg) to Wistar male rats resulted in a dose-related increase in liver tryptophan pyrrolase (TP) activity. The increase in brain serotonin (5-HT) concentration was not proportional to the dose given, and brain 5-HT concentration rapidly fell to the control (saline-treated) level or below. 2) The tryptophan-induced increase in liver TP activity was clearly prevented by DL-3-pyridylalanine (3-PA, 100 mg/kg). Serum free tryptophan and brain 5-HT… 
Inhibition of rat liver tryptophan pyrrolase activity and elevation of brain tryptophan concentration by administration of DL-alpha-amino-beta-pyridinepropanoic acid (pyridylalanine) analogs.
TLDR
It is suggested that PA analogs (and/or their metabolites) increased brain tryptophan (and hence 5-HT synthesis) by directly inhibiting liver TP activity by directly inhibition of holoenzyme activities in vitro.
Effects of combined administration ofl-tryptophan and tricyclic antidepressants on α2- and β-adrenoceptors and monoamine levels in rat brain
TLDR
The antidepressants appeared to interact withl-tryptophan to reduce its effects, and co-administration of a serotonin precursor with antidepressant drugs could potentiate the effects of the antidepressants on monoamines or adrenoceptors in rat brain.
L‐tryptophan administration and increase in cerebral serotonin levels: Systematic review