Peony roots are one of the most important herbal drugs prescribed in traditional Chinese medicine for the treatment of abdominal pain and stiffness of abdominal muscles, and the therapeutic effects are explained by the action of a characteristic constituent, paeoniflorin (PF, 1). Besides, related compounds (2-20) and tannins (21-28) are isolated hitherto and the total synthesis of some constituents and metabolites have been reported. The recent studies demonstrate that PF (1) improves the spatial learning deficits, and suggest possible uses of this agent in the treatment of dementia and age-related loss of cognitive function. Antispasmodic, hypotensive, depressant and anti- inflammatory effects, as well as a preventive effect on stress ulcer, relaxation of smooth muscles, an anticoagulant effect and inhibition of platelet aggregation, are also reported for PF (1).

Due to the poor absorption from intestine, PF (1) is subjected to the metabolism to give three metabolites, named paeonimetabolins I-III, by intestinal bacteria. Orally administered PF (1) to rats is scarcely absorbed from the gastrointestinal tract but rapidly eliminated from the plasma within a short period of time, while large amount of PM-I (39) formed is readily absorbed and retained in the plasma for a longer period of time as determined by enzyme immunoassay. PM-I (39) is not detected in the rat plasma after intravenous (i.v.) administration of PF (1), and a significant difference in the plasma concentration of PM-I (39) was observed between germ-free and conventional rats. After i.v. and oral (p.o.) administration of PF (1) at a dose of 5 mg/kg, the urinary and fecal excretions are 50.5 and 0.22% of the dose within 72 hrs, and 1.0 and 0.08% of the dose within 48 hrs, respectively. Cumulative biliary excretions of PF (1) after p.o. or i.v. administration to rats significantly vary. PM-I (39) is found at high concentrations in the plasma after p.o. and i.v. administration to rats. The pharmacokinetics of both PF (1) and PM-I (39) are dose-dependent.