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Tryptophan hydroxylase and 5-hydroxytryptamine in carcinoids of the gastrointestinal tract
Background:
Tryptophan hydroxylase is the enzyme that catalyzes the formation of 5-hydroxy-L-tryptophan which is the initial and rate-limiting enzyme in the biosynthesis of 5-hydroxytryptamine (serotonin). The aim of this study was to analyze the differential expression of tryptophan hydroxylase and 5-hydroxytryptamine in human gastrointestinal carcinoids.
Material And Methods:
Primary carcinoids and hepatic carcinoid metastases (n = 8) were investigated for the presence of tryptophan hydroxylase, 5-hydroxytryptamine and chromogranin A.
Results:
Only one of the tumors examined was immunoreactive for tryptophan hydroxylase, as determined by immunohistochemical techniques and Western blot analysis. All carcinoids expressed 5-hydroxytryptamine and chromogranin A.
Conclusions:
Carcinoids appear to be a heterogeneous group with respect to the expression of this monooxygenase. Based on these results it is proposed that other cells of the intestine are involved in the biosynthesis of 5-hydroxytryptamine precursors taken up by carcinoid tumor cells.