POTENTIATION OF THE BIOAVAILABILITY OF DAIDZIN BY AN EXTRACT OF RADIXPUERARIAE

The dose effect of pure daidzin on the suppression of ethanol intake i n Syrian golden hamsters was compared with that of crude daidzin conta ined in a methanol extract of Radix puerariae (RP). EC(50) values esti mated from the graded dose-response curves for pure daidzin and Rf ext ract daidzin are 23 and 2.3 mg per hamster per day, respectively. Appa rently the antidipsotropic activity of the RP extract cannot be accoun ted for solely by its daidzin content (22 mg/g). In addition to daidzi n, six other isoflavones were identified in the RP extract and quantif ied-namely, puerarin (160 mg per g of extract), genistin (3.7 mg/g), d aidzein (2.6 mg/g), daidzein-4',7-diglucoside (1.2 mg/g), genistein (0 .2 mg/g), and formononetin (0.16 mg/g). None of these, administered ei ther alone or combined, contributes in any significant way to the anti dipsotropic activity of the extract. Plasma daidzin concentration-time curves determined in hamsters administered various doses of pure daid zin or RP extract by i.p. injection indicate that the crude extract da idzin has approximate to 10 times greater bioavailability than the pur e compound. Reconstruction of the dose-response effects for pure and c rude daidzin using bioavailable daidzin rather than administered dose gives a single curve. Synthetic daidzin added to the RP extract acquir es the bioavailability of the endogenous daidzin that exists naturally in the extract. These results show that (i) daidzin is the major acti ve principle in methanol extracts of RP, and (ii) additional constitue nts in the methanol extract of RP assist uptake of daidzin in golden h amsters.