Summary
The catabolism of intraventricularly injected3H-(1)-norepinephrine (NE) by whole rat brain was studied at different time points. Particular attention was given to the formation and metabolic disposition of dihydroxyphenylethyleneglycol (DHPG). Following the intraventricular injection of3H-(1)-NE it was found that 1.0% of the total radioactivity present in whole rat brain was free3H-DHPG, 14.5% was present as conjugated3H-DHPG, and total3H-3-methoxy-4-hydroxyphenylethyleneglycol (3H-MHPG) accounted for 25% of the radioactivity in brain. These data indicate that MHPG and conjugated DHPG are the major products of brain NE and are present in the ratio of 2∶1.3H-DHPG was synthesized, purified, and its identity confirmed. The metabolism of free3H-DHPG in whole rat brain was studied following intraventricular administration. It was found that 30 min after injection 1.5% of the total radioactivity in whole rat brain was present as free3H-DHPG, 34% as conjugated3H-DHPG, 15% as free3H-MHPG, and 31% as conjugated3H-MHPG indicating that free DHPG is rapidly conjugated or converted to MHPG. Finally, in order to determine whether or not peripheral catabolism of intraventricularly administered3H-(1)-NE affects the observed distribution of the3H-metabolic products of norepinephrine present in whole rat brain, rats were pretreated with a MAO inhibitor (2, 9-dimethyl-β-carbolinium iodide [DMCI]) which does not cross the blood brain barrier and then received intraventricular injections of3H-(1)-NE. The amounts of the3H-metabolic products of norepinephrine were then determined. No differences were noted between the DMCI-treated and the control groups. This finding suggests that the observed distribution of the3H-metabolites present in whole rat brain after intraventricular administration of3H-(1)-NE is the products of central catabolism, per se.
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Abbreviations
- DHPG:
-
3,4-dihydroxyphenylethyleneglycol
- NE:
-
norepinephrine
- MHPG:
-
3-methoxy-4-hydroxyphenylethyleneglycol
- DMCI:
-
2,9-dimethyl-β-carbolinium iodide
- DHMA:
-
3, 4-dihydroxymandelic acid
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Supported in part by NIMH Grant MH 24393.
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Gale, S.W., Maas, J.W. A study of the formation and metabolic disposition of 3,4 dihydroxyphenylethyleneglycol in whole rat brain. J. Neural Transmission 41, 59–72 (1977). https://doi.org/10.1007/BF01252965
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DOI: https://doi.org/10.1007/BF01252965