The metabolic fate of rutin and quercetin in the animal body.

The finding of 3,4-dihydroxyphenylacetic acid (DHPAA) in the urine of rabbits after the oral ingestion of rutin or its aglycone quercetin has been reported from this Laboratory (1). In this same report it was stated that in each case after the administration of the flavonoid an examination of paper chromatograms of the ether extracts of the urine revealed the excretion of at least four metabolites (one of which was DHPAA). Two more of these four substances have now been identified (2) and a more detailed report is presented herein. One of these two compounds, m-hydroxyphenylacetic acid (mHPAA), was isolated and identified in this Laboratory over a year ago, but publication was withheld pending identification of the second compound, 3-methoxy-4-hydroxyphenylacetic acid (homovanillic acid). In the meantime, at least two other laboratories have reported the finding of mHPAA in control urines (3, 4). Also included in the present report are the results obtained from three species besides the rabbit, namely rats, guinea pigs, and humans. The metabolic fate of a flavonoid such as quercetin in animals other than the rabbit was considered especially important in view of the results obtained by Clark and MacKay with rats and humans (5).