5-Hydroxytryptophan (5-HTP), Plasma

In normal subjects, a small fraction of the essential amino acid L-Tryptophan is converted by Tryptophan hydroxylase to 5-Hydroxytryptophan (5-HTP), the intermediate metabolite in the biosynthesis of Serotonin, whereas the majority of L-Trptophan is converted to nicotinic acid. Serotonin levels have been implicated in the regulation of sleep, depression, anxiety, aggression, appetite, temperature, sexual behaviour, and pain sensation. See Also 5-HIAA and Serotonin

5-HTP is useful in the di%fferential diagnosis of carcinoid tumours. In carcinoid tumours, there is a shift in tryptophan metabolism towards serotonin through 5-hydroxytryptophan synthesis and eventually 5-HIAA. Forgut Carcinoid tumours secrete little serotonin but do secrete 5-HTP, while midgut tumours secrete high quantities of serotonin but rarely secrete 5-HTP.

2 ml EDTA Plasma Room Temperature

< 0.01 mg/dL