Short-term effects of 2,4,5-trihydroxyamphetamine, 2,4,5-trihydroxymethamphetamine and 3,4-dihydroxymethamphetamine on central tryptophan hydroxylase activity
Elayan I, Gibb JW, Hanson GR, Lim HK, Foltz RL, Johnson M.
Department of Pharmacology and Toxicology,
University of Utah, Salt Lake City.
J Pharmacol Exp Ther 1993 May;265(2):813-8


In previous studies, we have reported the long-term effects of several metabolites of 3,4-methylenedioxymethamphetamine (MDMA) on tryptophan hydroxylase (TPH) activity. In this study, the short-term effects of three metabolites of MDMA. 2,4,5-trihydroxyamphetamine (THA), 2,4,5-trihydroxymethamphetamine (THM) and 3,4-dihydroxymethamphetamine, and the in vitro effect of THA on TPH activity are reported. After short-term treatment, hippocampal TPH activity was decreased to 8 and 54% of control in response to THA and THM, respectively, but was unaltered after 3,4-dihydroxymethamphetamine. Incubating TPH from THM-treated rats with dithiothreitol under nitrogen failed to reverse the decrease in enzyme activity induced by THM treatment. THA also decreased tyrosine hydroxylase activity to 75% of control, whereas the enzyme activity remained unaltered by THM. The structural analog of THA, 6-hydroxydopamine, failed to reproduce the effect of THA on TPH activity; however, 5,6-dihydroxytryptamine decreased hippocampal TPH activity to 18% of control. In the in vitro study, the hippocampus and the striatum were incubated in varying concentrations of THA. After a 1-h incubation at 37 degrees C, hippocampal TPH activity was decreased to 83, 71, 68, 47 and 3% of control after exposure to 0.001, 0.01, 0.1, 0.5 or 5.0 mM THA, respectively; striatal TPH activity was reduced to 98, 95, 70, 54 and 17% of control, respectively. Incubating the enzyme under reducing conditions failed to restore the enzyme activity to control levels.

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