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912. Metabolism of some tea constituents in rabbits
874
NATURAL PRODUCTS
in 24 hr compared with about 2% in a patient with the syndrome. This work is consistent with the view of Eldjarn (Scand. J. clin. Lab. Invest. 1965, 17, 178) that the enzymatic defect probably occurs at the level of to-oxidation of the fatty acid. Whether there are other forms of metabolic impairment corresponding to Refsum's disease remains to be seen. 912. Metabolism of some tea constituents in rabbits
Watanabe, A. & Oshima, Y. (1965). Metabolism of gallic acid and tea catechin by rabbit. Agric. biol. Chem. 29, 90. Gallic acid (3,4,5-trihydroxybenzoic acid; I) is ingested by man in the free form and as derivatives present in tea, such as gallocatechin (II) which represents about 5% of the tea catechins. Korpassy (Prog. exp. Tumor Res. 1961, 2, 245) has referred to the non-carcinogenicity of tea'catechin, in contrast with other tannins. This study deals with the metabolism of I and II in the rabbit and besides giving information on the nature of the metabolites also indicates interesting effects of I on the metabolism of other phenolic compounds. After feeding relatively large amounts of I (0.5 g/kg) to rabbits, most was excreted unchanged in the urine and some metabolized to pyrogallol by decarboxylation and to 4methoxy-3,5-dihydroxybenzoic acid by O-methylation. The same two metabolites were identified in the urine following oral administration of II in the form of tea catechin and were presumably derived from I present as a conjugate in II. However, the trihydroxyphenyl moiety of II could not be detected indicating, presumably, that this is rapidly metabolized in the rabbit. The most interesting finding was that three phenolic acids, homovanillic acid, homoprotocatechuic acid and m-hydroxyphenylacetic acid, characteristically present in the urine of control rabbits, were absent from the urine of the animals fed 0.5 g I/kg. Since these acids could be formed from dihydroxyphenylalanine [dopa] (Fig. 1) it is considered that oral ingestion of large amounts of I affects the metabolism of phenolic compounds such as dopa and could have caused the disappearance of these phenolic acids from the urine. OH
OCH3 OH
OH
CH2
CH2
CHNH2
COOH
t I
COOH
Dihydroxyphenylolonine
CHz I COOH Homovonitlic acid
I
Homoprotocatechuic acid
~
OH
cH~ COOH
m- Hydroxyphenylocetic acid FIG. 1. Formation of phenolic acids from dihydloxyphenylalanin¢ (dopa).
Dopa is of additional current interest since it has been held responsible for the hypertensive crises arising in patients on monoamine-oxidase inhibitors following ingestion of broad beans (Cited in F.C.T. 1964, 2, 488; p. 839 of this issue).
NATURAL PRODUCTS
in 24 hr compared with about 2% in a patient with the syndrome. This work is consistent with the view of Eldjarn (Scand. J. clin. Lab. Invest. 1965, 17, 178) that the enzymatic defect probably occurs at the level of to-oxidation of the fatty acid. Whether there are other forms of metabolic impairment corresponding to Refsum's disease remains to be seen. 912. Metabolism of some tea constituents in rabbits
Watanabe, A. & Oshima, Y. (1965). Metabolism of gallic acid and tea catechin by rabbit. Agric. biol. Chem. 29, 90. Gallic acid (3,4,5-trihydroxybenzoic acid; I) is ingested by man in the free form and as derivatives present in tea, such as gallocatechin (II) which represents about 5% of the tea catechins. Korpassy (Prog. exp. Tumor Res. 1961, 2, 245) has referred to the non-carcinogenicity of tea'catechin, in contrast with other tannins. This study deals with the metabolism of I and II in the rabbit and besides giving information on the nature of the metabolites also indicates interesting effects of I on the metabolism of other phenolic compounds. After feeding relatively large amounts of I (0.5 g/kg) to rabbits, most was excreted unchanged in the urine and some metabolized to pyrogallol by decarboxylation and to 4methoxy-3,5-dihydroxybenzoic acid by O-methylation. The same two metabolites were identified in the urine following oral administration of II in the form of tea catechin and were presumably derived from I present as a conjugate in II. However, the trihydroxyphenyl moiety of II could not be detected indicating, presumably, that this is rapidly metabolized in the rabbit. The most interesting finding was that three phenolic acids, homovanillic acid, homoprotocatechuic acid and m-hydroxyphenylacetic acid, characteristically present in the urine of control rabbits, were absent from the urine of the animals fed 0.5 g I/kg. Since these acids could be formed from dihydroxyphenylalanine [dopa] (Fig. 1) it is considered that oral ingestion of large amounts of I affects the metabolism of phenolic compounds such as dopa and could have caused the disappearance of these phenolic acids from the urine. OH
OCH3 OH
OH
CH2
CH2
CHNH2
COOH
t I
COOH
Dihydroxyphenylolonine
CHz I COOH Homovonitlic acid
I
Homoprotocatechuic acid
~
OH
cH~ COOH
m- Hydroxyphenylocetic acid FIG. 1. Formation of phenolic acids from dihydloxyphenylalanin¢ (dopa).
Dopa is of additional current interest since it has been held responsible for the hypertensive crises arising in patients on monoamine-oxidase inhibitors following ingestion of broad beans (Cited in F.C.T. 1964, 2, 488; p. 839 of this issue).