BLOOD AND URINE 5-HYDROXYTRYPTOPHAN AND 5-HYDROXYTRYPTAMINE LEVELS AFTER ADMINISTRATION OF 2 5-HYDROXYTRYPTAMINE PRECURSORS IN NORMAL MAN

Six healthy male subjects received equimolar amounts of two 5-hydroxyt ryptamine (5-HT) precursors, 5-hydroxy-L-tryptophan (5-HTP) and gamma- L-glutamyl-5-hydroxy-L-tryptophan (glu-5-HTP), on two occasions in a r andomised cross-over study. There were marked increases in urinary 5-H TP and 5-HT excretion after infusion of both compounds. Mean urinary e xcretion rate of 5-HT, which was < 0.7 nmol min(-1) before dosing, ros e to a peak value of 412 +/- 92 nmol min(-1) at the end of 5-HTP infus ion and 303 +/- 29 nmol min(-1) after administration of glu-5-HTP. Thi s occurred without significant changes in blood 5-HT levels measured i n platelet-rich plasma. These findings provide further evidence that t he increase in urine 5-HT after administration of both 5-HT precursors is largely due to 5-HT synthesised within the kidney.