title: Tryptophan hydroxylase and 5-hydroxytryptamine in carcinoids of the gastrointestinal tract.
abstract: 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.
  
  
  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.
authors.affiliation: Department of Gastroenteropathology, University of Göttingen, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Brinck
authors.forename: T
authors.initials: T
authors.lastname: Meyer
mesh_terms: D002276:Carcinoid Tumor / Q000737:chemistry*; D002864:Chromogranins / Q000032:analysis; D006801:Humans; D007150:Immunohistochemistry; D007414:Intestinal Neoplasms / Q000737:chemistry*; D012701:Serotonin / Q000032:analysis* / Q000096:biosynthesis; D014365:Tryptophan Hydroxylase / Q000378:metabolism*
chemical_list: D002864:Chromogranins; D012701:Serotonin; D014365:Tryptophan Hydroxylase