Which Factors Affect the Availability of Tryptophan for Central Serotonin Synthesis?

Influence of tryptophan on the serotonin system in the brain


The conversion of tryptophan (tryp) to 5-hydroxytryptophan and eventually to 5-hydroxytryptamine (serotonin) in den CNS may be stimulated by the exogenous supply of tryp. A constant supply of free tryp at the blood-brain barrier seems to be required to ensure an adequate synthesis of serotonin in the brain.


After crossing the blood-brain barrier, tryp is hydroxylated by the enzyme tryptophan hydroxylase. This reaction is the rate-limiting step in the synthesis of serotonin. Tryptophan hydroxylase is only half-saturated under physiological conditions (Young and Gautier 1981) and its activity can be further stimulated by a high substrate supply (Fernstrom and Wurtman 1972, Heuther et al. 1992). In other terms, a high concentration of free tryptophan at the blood-brain barrier leads to the increased formation of 5-hydroxytryptophan (5-HTP), a precursor of serotonin (5-hydroxytryptamine). It should be noted that deficiencies of vitamin B6 (Hvas et al 2004) and magnesium (Durlach J. et al 2002, Korbitz BC. 1970) inhibit the activity of the enzyme and thus reduce serotonin synthesis. The same applies to caffeine which equally reduces the activity of tryptophan hydroxylase (Lim et al 2001). Regular consumption of coffee may therefore have an adverse effect on serotonin synthesis.

Link: Tryptphan Literature

 

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