The neuronal and extraneuronal disposition of3H-7,8-and3H-7-labelled (−)-noradrenaline and dopamine was compared in in vitro studies.
In agreement with earlier studies, the present results show that the presence of a tritium label in position 8 (i.e., on the alpha-carbon) has two consequences: a) the rate of deamination declines and b) part of the deamination results in the formation of an unlabelled aldehyde plus tritium water; tritium water is recovered from the OMDA-fraction of the column chromatographic procedure of Graefe et al. (1973).
Whenever the deamination of a3H-catecholamine is reduced (by tritium in position 8), the intraneuronal3H-catecholamine concentration is increased. This increase, in turn, partly masks the decline in neuronal deamination (rat vas deferens). Irrespective of whether one dertermines the spontaneous efflux, the release of3H-noradrenaline by nerve stimulation or the release of3H-(−)-noradrenaline by the reserpine-like compound Ro 4-1284, the presence of tritium in position 8 distorts the results (experiments with rat vasa deferentia and/or rabbit aorta).
In the extraneuronal system of the rat heart, two intracellular enzymes inactivate3H-(−)-noradrenaline and3H-dopamine: catechol-O-methyl transferase (COMT) and monoamine oxidase (MAO). Any hindrance of deamination (by tritium in position 8, COMT intact) leads to a shift of the metabolism of the3H-catecholamines from the exclusively deaminated to the exclusively O-methylated metabolites.
No differences between3H-7,8-and3H-7-labelled catecholamines were found after inhibition of MAO and COMT (extraneuronal accumulation and rate constant for efflux from the extraneuronal compartment III of the rat heart).
These results indicate that the presence of tritium in position 8 of catecholamines introduces errors, if monoamine oxidase is active. This is important for the interpretation of earlier results, since virtually all samples of “3H-(−)-noradrenaline” and “3H-dopamine nominally labelled in position 7” were contaminated with varying amounts of tritium in position 8.
In some experiments, also3H-7-(−)-adrenaline was used. For adrenergic nerve endings, the rate of metabolism (deamination) declined in the order:3H-7-dopamine > 3H-7-(−)-noradrenaline > 3H-7-(−)-adrenaline. For the extraneuronal disposition the ranking order was:3H-7-(−)-adrenaline > 3H-7-(−)-noradrenaline=3H-7-dopamine. However, in the extraneuronal disposition of3H-(−)-adrenaline, O-methylation predominated over deamination.
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the fraction containing all metabolites that are both deaminated and O-methylated
the fraction containingall O-methylated metabolites, deaminated or not; Note that tritium water appears in the OMDA- or OM-fraction
Fiebig ER, Trendelenburg U (1978) The neuronal and extraneuronal uptake and metabolism of3H-(−)-noradrenaline in the perfused rat heart. Naunyn-Schmiedeberg's Arch Pharmacol 303:21–35
Graefe K-H, Stefano FJE, Langer SZ (1973) Preferential metabolism of (−)-3H-norepinephrine through the deaminated glycol in the rat vas deferens. Biochem Pharmacol 22:1147–1160
Grohmann M, Trendelenburg U (1983) The isotope effect of tritium in3H-(−)-adrenaline with very high specific activity. Naunyn-Schmiedeberg's Arch Pharmacol 324:233–234
Grohmann M, Trendelenburg U (1984) The substrate specificity of uptake2 in the rat heart. Naunyn-Schmiedeberg's Arch Pharmacol 328:164–173
Henseling M (1983) The influence of uptake2 on the inhibition by unlabelled noradrenaline of the stimulation-evoked overflow of3H-noradrenaline in rabbit aorta with regard to surface of amine entry. Naunyn-Schmiedeberg's Arch Pharmacol 324: 99–107
Henseling M, Eckert E, Trendelenburg U (1976) The distribution of3H-(±)-noradrenaline in rabbit aortic strips after inhibition of the noradrenaline-metabolizing enzymes. Naunyn-Schmiedeberg's Arch Pharmacol 292:205–217
Keller B, Graefe K-H (1979) The inhibitory effect of some monovalent cations on the stimulation by Na+ of the neuronal uptake of noradrenaline. Naunyn-Schmiedeberg's Arch Pharmacol 309:89–97
Paiva QM, Guimaraes S (1978) A comparative study of the uptake and metabolism of noradrenaline and adrenaline by the isolated saphenous vein of the dog. Naunyn-Schmiedeberg's Arch Pharmacol 303:221–228
Sncdecor GW, Cochran WG (1980) Statistical methods, 7th edn. Iowa State University Press, Ames
Snyder SH, Coyle T (1969) Regional differences in3H-norepinephrine and3H-dopamine uptake into rat brain homogenates. J Pharmacol Exp Ther 165:78–86
Starke K, Steppeler A, Zumstein A, Henseling M, Trendelenburg U (1980) False labelling of commercially available3H-catecholamines? Naunyn-Schmiedeberg's Arch Pharmacol 311: 109–112
Stute N, Trendelenburg U (1984) The outward transport of axoplasmic noradrenaline induced by a rise of the sodium concentration in the adrenergic nerve endings of the rat vas deferens. Naunyn-Schmiedeberg's Arch Pharmacol 327:124–132
Trendelenburg U (1984a) Metabolizing systems. In: Fleming WW, Langer SZ, Graefe K-H, Weiner N (ed) Neuronal and extraneuronal events in autonomic pharmacology. Raven Press, New York, pp 93–109
Trendelenburg U (1984b) The influence of inhibition of catechol-O-methyl transferase or of monoamine oxidase on the extraneuronal metabolism of3H-(−)-noradrenaline in the rat heart. Naunyn-Schmiedeberg's Arch Pharmacol 327:285–292
Trendelenburg U, Fleig H, Bryan LJ, Bönisch H (1983a) The extraneuronal compartments for the distribution of isoprenaline in the rat heart. Naunyn-Schmiedeberg's Arch Pharmacol 324: 169–179
Trendelenburg U, Stefano FJE, Grohmann M (1983b) The isotope effect of tritium in3H-noradrenaline. Naunyn-Schmiedeberg's Arch Pharmacol 323:128–140
Supported by the Deutsche Forschungsgemeinschaft
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Grohmann, M., Henseling, M., Cassis, L. et al. Errors introduced by a tritium label in position 8 of catecholamines. Naunyn-Schmiedeberg's Arch. Pharmacol. 332, 34–42 (1986). https://doi.org/10.1007/BF00633194
- Neuronal deamination
- Extraneuronal deamination
- Isotope effects