Tryptoline is a natural organic derivative of beta-carboline. It is an alkaloid chemically related to tryptamines. 5-Hydroxytryptoline and 5-methoxytryptoline (pinoline) are the most active monoamine oxidase inhibitors (MAOIs) with IC50s of 0.5 μM and 1.5 μM respectively, using 5-hydroxytryptamine (serotonin) as substrate. Tryptolines are also potent reuptake inhibitors of serotonin and epinephrine, with a significantly greater selectivity for serotonin. Comparison of the inhibition kinetics of tetrahydro-β-carbolines for serotonin and epinephrine reuptake to that of the platelet aggregation response to these amines has shown that 5-hydroxymethtryptoline, methtryptoline, and tryptoline are poor inhibitors of reuptake. In all respects 5-hydroxytryptoline and 5-methoxytryptoline showed greater pharmacological activity than the tryptoline and methtryptoline.
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