Urinary Excretion of Tryptamine in Comparison to Normetanephrine and Beta-Phenylethylamine in Human Volunteers After Subchronic Treatment with Different Monoamine Oxidase Inhibitors
Measurement of urinary tryptamine excretion has been used extensively in the past as indicator for monoamine oxidase (MAO) inhibition in man. Basal tryptamine excretion (ug/g creatinine) differs between sexes (p< 0.001). The values obtained (x ± SD) were: 66 ± 26 in 13 males (n = 90) and 112 ± 42 in 9 females (n = 60). The higher basal tryptamine excretion and the larger tryptamine/indole acetic acid ratios in females, together with the greater effect of MAO inhibitors suggest a lower basal MAO-A activity in women. Different hormonal influences could explain the large interindividual and intraindividual seasonal variation of tryptamine excretion in females. By comparison of urinary tryptamine, normetanephrine and beta-phenylethylamine during subchronic treatment with three different MAO inhibitors it could be shown that tryptamine is a MAO-A substrate. MAO-A inhibition by the new reversible selective inhibitor CGP 11 305 A (150mg/d) caused parallel increases of tryptamine (320%) and normetanephrine (360%), but did not change urinary phenylethylamine. Selective MAO-B inhibition with deprenyl (10mg/d) enhanced phenylethylamine excretion (2600%), but did not affect tryptamine. During treatment with tranylcypromine (20mg/d), the unspecific inhibitor of both MAO-A+B, all three metabolites increased significantly (between 440% and 720%).
KeywordsMonoamine Oxidase Indole Acetic Acid Monoamine Oxidase Activity Subchronic Treatment Trace Amine
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