Inhibition of dopa decarboxylase by the hydrazino analog of α-methyldopa
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Keywords:
Carbidopa
Decarboxylase inhibitor
Pargyline
5-Hydroxytryptophan
Monoamine oxidase inhibitor
Pargyline
Submucous plexus
Monoamine oxidase inhibitor
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Decarboxylase inhibitor
Reserpine
5-Hydroxytryptophan
Cell bodies
Hydrazine (antidepressant)
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While the 5-HT precursors tryptophan and 1-5-HTP cause an increase in serum prolactin concentration, a combination of 1-5-HTP with a peripheral decarboxylase inhibitor was found to reduce the serum prolactin concentration. This combination seemed to behave like a DA agonist. This effect is not produced by the decarboxylase inhibitor per se. A possible explanation is that 5-HTP is converted to 5-HT in CA-ergic neurons, that 5-HT supersedes the CA from the stores, and that some of the CA reach the synaptic cleft and stimulate CA receptors. Another possible explanation is that 5-HTP decarboxylase is centrally inhibited as well, and that an effect of 5-HTP itself is involved here. In view of the observations made it is doubtful whether the therapeutic effect of 5-HTP combined with a peripheral decarboxylase inhibitor in depressions and myoclonus can in fact be atributed to activation of central serotonergic systems.
Decarboxylase inhibitor
5-Hydroxytryptophan
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Abstract 5‐Hydroxytryptophan has been found to be beneficial when administered alone or in combination with extracerebral aromatic amino acid decarboxylase inhibitors for therapeutic purposes in various disorders in which myoclonus is prominent. In five subjects the effect of decarboxylase inhibitors on the accumulation and elimination of 5‐hydroxytryptophan in plasma was studied. The plasma concentrations of 5‐hydroxytryptophan were increased about ten fold by pretreatment with the decarboxylase inhibitors, carbidopa and benserazide. Half‐lives of 2.2‐3.0 hrs. were obtained following oral administration of a single dose of 5‐hydroxytryptophan with or without pretreatment. In one subject the half‐life of 5 hydroxytryptophan in plasma increased to 5.5 hrs. during long‐term treatment with carbidopa.
Benserazide
Carbidopa
5-Hydroxytryptophan
Decarboxylase inhibitor
Plasma levels
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Benserazide
Carbidopa
5-Hydroxytryptophan
Decarboxylase inhibitor
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5-Hydroxytryptophan
Polysome
Monoamine oxidase inhibitor
Reserpine
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5-Hydroxytryptophan
Decarboxylase inhibitor
Decarboxylation
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Benserazide
Carbidopa
Decarboxylase inhibitor
5-Hydroxytryptophan
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Abstract Using an enzyme preparation from rabbit kidney cortex, the amino acids 3,4‐dihydroxyphenylalanine and 5‐hydroxytryptophan were found to inhibit each other's enzymatic decarboxylation competitively. Competitive inhibitions of these reactions by m‐tyrosine, o‐tyrosine, and caffeic acid were also observed. After purification of an enzyme preparation on a column of DEAE cellulose a peak appeared which contained most of the dihydroxyphenylalanine decarboxylase activity present in the extract. In this peak also nearly all the 5‐hydroxytryptophan decarboxylase activity was found. The ratio of the two activities was practically the same throughout the peak. The data were in agreement with the assumption that dihydroxyphenylalanine and 5‐hydroxytryptophan were decarboxylated by one enzyme.
Dihydroxyphenylalanine
Decarboxylation
5-Hydroxytryptophan
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