In vivo studies of the tryptophan-5-hydroxylase system. Quantitation of serotonin and tryptamine using gas chromatography-mass fragmentography.
An in vivo determination of tryptophan-5-hydroxylase (E.C. 1.14.16.4) activity is described. Subjects were loaded with deuterated L-tryptophan-d5 (50 mg/kg body weight) and the deuterated serotonin-d4 in urine was analysed using mass fragmentography. Four control subjects were dosed orally and two of them also intravenously with 50 mg/kg of L-tryptophan-d5. One patient with atypical phenylketonuria (PKU) due to a tetrahydrobiopterin (BH4) deficiency was dosed without and during BH4 treatment. Without BH4, the patient showed only minor formation of deuterated serotonin. After BH4 administration (2.5 mg/kg body weight) the serotonin formation increased about four-fold but was not normalized. Serotonin in urine and blood was analysed as the pentafluoropropionyl (PFP) derivative using gas chromatography-mass fragmentography. Deuterated serotonin was used as internal standard. The analysis of tryptamine can be performed with the same procedure.
D001708:Biopterins / Q000378:metabolism / Q000627:therapeutic use; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D010661:Phenylketonurias / Q000188:drug therapy / Q000652:urine; D012701:Serotonin / Q000097:blood / Q000652:urine*; D014364:Tryptophan / Q000494:pharmacology; D014365:Tryptophan Hydroxylase / Q000378:metabolism*
D001708:Biopterins; D012701:Serotonin; D014364:Tryptophan; D014365:Tryptophan Hydroxylase