In vitro neuronal and vascular responses to 5-hydroxytryptamine: modulation by 4-methylthioamphetamine, 4-methylthiomethamphetamine and 3,4-methylenedioxymethamphetamine
by
Murphy J, Flynn J, Cannon D, Guiry P,
McCormack P, Baird A, McBean G, Keenan A.
Department of Biochemistry,
Conway Institute of Biomolecular and Biomedical Research,
University College Dublin, 4, Dublin, Ireland
Eur J Pharmacol 2002 May 24;444(1-2):61

ABSTRACT

4-Methylthioamphetamine and 4-methylthiomethamphetamine are thioarylethylamines structurally related to 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy'). This study compared effects of these agents and MDMA on 5-hydroxytryptamine (5-HT) signalling systems in the brain and vasculature in vitro. Both 4-methylthioamphetamine and 4-methylthiomethamphetamine (100 &mgr;M) reduced the rate of specific high affinity [3H]5-HT reuptake in isolated rat brain synaptosomes to 14% and 10% of control, respectively. The concentration required for half-maximal inhibition (IC(50)) of [3H]5-HT reuptake by 4-methylthioamphetamine (0.27 &mgr;M) was significantly lower (P<0.005) than that for inhibition by MDMA (1.28 &mgr;M) and that for inhibition by 4-methylthiomethamphetamine (0.89 &mgr;M). Both 4-MTA and 4-MTMA caused a significant release of preloaded [3H]5-HT from synaptosomes, but were significantly less effective than MDMA at the concentrations tested (1-100 &mgr;M). In isolated rat aorta, a 15-min preincubation with 4-methylthioamphetamine or 4-methylthiomethamphetamine significantly reduced the maximal contraction (E(max)) induced by 5-HT to 71% or 91% of control (P<0.05 in each case), respectively. In addition, 4-methylthiomethamphetamine (100 &mgr;M), but not 4-methylthioamphetamine, significantly increased the concentration of 5-HT required for half-maximal contraction (EC(50)) from 4.13 to 20.08 &mgr;M (P<0.0001). In contrast, MDMA did not significantly alter the E(max) or the EC(50) of 5-HT-induced aortic contraction. It is concluded that both 4-methylthioamphetamine and 4-methylthiomethamphetamine are potent inhibitors of [3H]5-HT reuptake in the brain. Furthermore, unlike MDMA, they both directly inhibit 5-HT-mediated vascular contraction. These results suggest that these compounds may be potentially more harmful than MDMA in the context of human misuse.

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