Absorption of quercetin, a flavonoid regarded as a beneficial dietary factor, was studied in rats.The compound was administered orally in propylene glycol, water/propylene glycol, and water.Quercetin's solubility in vehicles used for quercetin administration was measured. Followingadministration, tail vein blood was collected as a function of time. Concentrations of quercetin andits metabolites in rat blood plasma were measured by HPLC with electrochemical detection afterhydrolysis of respective conjugates with
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-glucuronidase and/or sulfatase. Pharmacokinetic profilesof quercetin and isorhamnetin, its 3'-methoxy derivative, were obtained, and on their basis it wasconcluded that isorhamnetin was present in rat blood plasma mainly as sulfate/glucuronideconjugates. Quercetin's solubility in solvents used for its administration was compared withrespective absorption profiles. This comparison revealed that solubilization enhanced quercetinabsorption; however, its lack was not an absorption-limiting factor.Keywords: Flavonoid absorption; quercetin; isorhamnetin; glucuronide; rat