1. than normal levels before obvious improvement;Anden, N.-E.; Roos, B.-E.; Werdinius, B.;Life Sci; in clinical status becomes apparent, it is probable On the occurrence of homovanillic acid in brain and that only a very small proportion of these metabolites arises from the turnover of intraneuronal dopamine derived from the administered L-dopa. Extraneuronal dopamine formation in the brains of cerebrospinal fluid and its determination by a fluorometric method,1963
2. Homovanillic acid, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindol-3-ylacetic acid in animals treated with dopa has been demonstrated histochemically;Ashcroft, G.W.; Crawford, T.B.B.; C., Dow R.; Guldberg, H.C.,1968
3. In addition to a different cellular site of formation of dopamine and its metabolites, there is the possibility of different metabolic routes of formation of the acids. For instance, HVA could be derived theoretically from dopa through oxidative deamination of 3-0-methyldopamine formed by decarboxylation of 3-0-methyl dopa. This pathway would bypass the formation of the biologically active amine, dopamine, in the production of HVA. The 0methylated amino acid and HVA were the only labelled metabolites found by Pletscher, Bartholini, and Tissot,1967
4. methyl dopa has been reported to be a very poor substrate for dopa decarboxylase (Ferrini and Glasser, 1964) and the extensive formation of HVA via the intermediary formation of 3-0-methyl dopa seems, on present evidence, unlikely
5. The pathogenesis of Parkinson's disease. A new hypothesis;Barbeau, A.;Canad. med. Ass. J,1962