The uptake and metabolism of 3H-catecholamines in rat cerebral cortex slices |
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Authors: | U Trendelenburg |
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Institution: | (1) Institut für Pharmakologie und Toxikologie, Universität Wurzburg, Versbacher Strasse 9, D-8700 Würzburg, Federal Republic of Germany |
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Abstract: | Summary The accumulation and metabolism of 3H-catecholamines were studied in cerebral cortex slices obtained from rats pretreated with reserpine, during 30 min of incubation with 50 nmol/l of the 3H-amines. In some experiments neuronal uptake (uptake,) was inhibited by the presence of 0.3 mol/l desipramine, in others COMT was inhibited by 30 mol/l U-0521. When both MAO and COMT were intact, most of the metabolism of 3H-noradrenaline was neuronal (i. e., desipramine-sensitive). For 3H-adrenaline rates of neuronal metabolism were much lower than for 3H-noradrenaline, non-neuronal O-methylation accounting for about 50% of total metabolism. Rates of metabolism of 3H-dopamine were similar to those of 3H-noradrenaline, but with a predominance of non-neuronal metabolism, which involved O-methylation and deamination. Under these conditions, very little 3H-catecholamine was recovered from the tissues; moreover, desipramine tended to increase tissue levels. Hence, tissue content then appears to partly reflect extracellularly distributed 3H-amines. After block of MAO rates of metabolism of 3H-noradrenaline and 3H-dopamine were greatly reduced, and tissue levels were increased. Desipramine now antagonized the accumulation of 3H-amines in the tissue, while U-0521 increased it. Rates of O-methylation (in the presence of desipramine) increased in the order 3H-noradrenaline < 3H-dopamine. It is concluded that neuronal uptake is associated with MAO only, and rates of neuronal deamination increased in the order: 3H-adrenaline < 3H-dopamine « 3H-noradrenaline. Non-neuronal uptake is associated with both, COMT and MAO, and rates of non-neuronal metabolism increased in the order: 3H-adrenaline < 3H-noradrenaline « 3H-dopamine.Abbreviations COMT
catechol-O-methyl transferase
- DOMA
dihydroxymandelic acid
- DOPAC
dihydroxyphenylacetic acid
- DOPEG
dihydroxyphenylglycol
- DOPET
dihydroxyphenylethanol
- HVA
homovanillic acid
- MAO
monoamine oxidase
- MN
metanephrine
- MOPEG
methoxyhydroxyphenylglycol
- MOPET
methoxyhydroxyphenylethanol
- NMN
normetanephrine
- 3-OMT
3-O-methyl-tyramine
- VMA
vanillylmandelic acid
Supported by the Deutsche Forschungsgemeinschaft (SFB 176)
Send offprint requests to U. Trendelenburg at the above addresswith the technical assistance of M. Babl |
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Keywords: | Central cortex slices Neuronal uptake Non-neuronal uptake Catechol-O-methyl transferase Monoamine oxidase 3H-catecholamines |
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