Effects of Exogenous L-Dopa on the Metabolism of Methionine and S-Adenosylmethionine in the Brain
The catecholamines dopamine, norepinephrine, and epinephrine are metabolized by oxidative deamination and by O-methylation. This latter pathway is catalyzed by the enzyme catechol-O-methyl-transferase (1); it utilizes S-adenosyl-methionine (SAMe) as the methyl donor (Fig. 1), and its products are, for the most part, methylated on the metahydroxyl group. The catecholamines themselves are formed within only a few specific tissues in the body (21). These include a relatively small number of brain neurons, postganglionic sympathetic neurons, adrenomedullary chromaffin cells, and interneurons within sympathetic ganglia. The catechol-amines can be O-methylated within their cells of origin, within synapses, or, after secretion into the blood stream, within the liver, kidneys, and other organs.
KeywordsMethionine Adenosyltransferase Methionine Concentration Postganglionic Sympathetic Neuron Homocysteine Methyltransferase Methyl Group Metabolism
Unable to display preview. Download preview PDF.
- 3.Bartholini, G., Pletscher, A.: Cerebral accumulation and metabolism of C14-dopa after selective inhibition of peripheral decarboxylase. J. Pharmacol, exp. Ther. 161 14(1968)Google Scholar
- 7.Chalmers, J.P., Baldessarini, R.J., Wurtman, R.J.: Effects of L-dopa on norepinephrine metabolism in the brain. Proc. nat. Acad. Sei. (Wash) 68, 662 (1971)Google Scholar
- 16.Ordonez, L.A., Ambrus, M., Boyson, S., Goodman, M.N., Ruderman, N.B., Wurtman, R.J.: Skeletal muscle: Reservoir for exogenously administered L-dopa. J. Pharmacol., exp. Ther. 190, 187 (1974)Google Scholar
- 18.Romero, J.A., Chalmers, J.P., Cottman, K., Lytle, L.D., Wurtman, R.J.: Regional effects of L-dihydroxyphenylalanine (L-dopa) on norepinephrine metabolism in rat brain. J. Pharmacol, exp. Ther. 180, 277 (1972)Google Scholar
- 19.Romero, J.A., Lytle, L.D., Ordonez, L.A., Wurtman, R.J.: Effects of L-dopa administration on the concentrations of dopa, dopamine, and norepinephrine in various rat tissues. J. Pharmacol, exp. Ther. 184, 67 (1973)Google Scholar
- 21.Wurtman, R.J.: Catecholamines. Boston: Little, Brown and Co., 1966Google Scholar
- 22.Wurtman, R.J., Chou, C, Rose, C: The fate of Cl4-dihydroxyphenylalanine in the whole mouse. J. Pharmacol, exp. Ther. 174, 351 (1970a)Google Scholar