5-Hydroxytryptophan inhibitors

Kahn RS, Westenberg HGM L-5-Hydroxytryptophan in the treatment of anxiety disorders. J Affect Disord 8 197-200, 1985 Kahn RS, Westenberg HGM, Verhoeven WMA, et al Effects of a serotonin precursor and uptake inhibitor in anxiety disorders a double-blind comparison of 5-hydroxytryptophan, clomipramine and placebo. Int J Clin Psychopharmacol 2 33-45, 1987... 

Serotonin is synthesized via tryptophan and 5-hydroxytryptophan with decarboxylation of the latter (Fig. 25-12). Within the pineal body of the brain and in the retina, serotonin is acetylated to N-acetylseroto-nin,782/783 which is then O-methylated to melatonin, the pineal hormone (Fig. 25-12). A specific inhibitor of serotonin synthesis is p-chlorophenylalanine, and studies with this and other inhibitors suggest that serotonin is required for sleep.784... 

As mentioned above, the existence of H3 receptors located presynaptically as heteroreceptors on other aminergic neurons, such as serotonergic, noradrenergic and dopaminergic neurons has been suggested [10-13], However, in a series of experiments we found that neither RmHA nor THIOP affected the ACTH response to serotonergic activation induced by administration of the 5-HT precursor 5-hydroxytryptophan in combination with the 5-HT re-uptake inhibitor fluoxetine [27],... 

Tryptophan is a precursor of serotonin (5-hydroxytryptamine) and the authors point out that the symptoms resemble the serotonin syndrome, which occurs when serotonin levels are increased. They warn against the concurrent use of tryptophan with fluoxetine or other serotonin reuptake inhibitors. This caution is echoed by most of the manufacturers of the SSRIs the UK manufacturer of paroxetine additionally mentions oxitriptan [L-5-hydroxytryptophan]... 

Smith, S. E., The pharmacological actions of 3,4-dihydroxyphenyl-a-methylalanine (a-methyldopa), and inhibitor of 5-hydroxytryptophan decarboxylase, Brit. J. Pharmacol. 15, 319 (1960). 

Pharmacological evidence was obtained several years ago that indicated that tryptophan is decarboxylated to tryptamine by both animal and bacterial enzymes. More recent studies have failed to detect this reaction, but instead have shown decarboxylation to occur only after oxidation of the indole nucleus to yield 5-hydroxytryptophan. Decarboxylation of 5-hydroxytryptophan produces 5-hydroxytryptamine, serotonin, which has important, though incompletely defined functions in animal physiology. In some animal livers there is an enzyme that decarboxylates cysteic acid to taurine. Glutamic decarboxylase has been found in animal brain, where it is responsible for the formation of 7-aminobutyric acid. This product has been implicated in nervous function as an inhibitor of synaptic transmission. ... 

A, adrenaline COMT, catechol-O-methyl transferase CSF, cerebrospinal fluid DA, 3,4-dihydroxyphenylethylamine (dopamine) Dopa, 3,4-dihydroxyphenylalanine 5HIAA, 5-hydroxyindoleacetic acid 5HT, 5-hydroxytryptamine (serotonin) 5HTP, 5-hydroxytryptophan HVA, 3-methoxy-4-hydroxyphenylacetic acid (homovanillic acid) MAO, monoamine oxidase MAOI, monoamine oxidase inhibitor MHPG,... 

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