STRUCTURAL TRANSFORMATION OF LIGNAN COMPOUNDS IN RAT GASTROINTESTINAL-TRACT .2. SERUM CONCENTRATION OF LIGNANS AND THEIR METABOLITES

Serum concentrations of arctiin, tracheloside, and their metabolites f ormed in the gastrointestinal tract were investigated in the rat. Arct iin or tracheloside was not detected in the serum after oral administr ation (200 mg/kg). In regard to their metabolites, each metabolite 1 ( AM1, TM1), their genuine genins, appeared in the serum , and the serum concentration of arctiin metabolite 1 (AM1) reached its peak at 4 h a nd that of tracheloside metabolite 1 (TM1) reached its peak at 8 h. On the other hand, both metabolites 2 (AM2, TM2), which each possess a c atechol moiety as reported previously, were not found in the serum. No w, we have studied the detection of their metabolites in the rat large intestinal contents after oral administration. It was revealed that a ll metabolites reported previously were certainly formed in rat gastro intestinal tract in vivo. Thus, we presumed a possibility that metabol ite 2 was converted into metabolite 1 through C-3'' methylation by cat echol-O-methyltransferase (COMT) in rat liver. Each metabolite 2 was i ncubated with rat liver cytosol in the presence of S-adenosyl-L-methio nine. It was proved that metabolite 2 was rapidly converted into metab olite 1 within 3 min. We suggest that arctiin or tracheloside was tran sformed to at least two metabolites in the gastrointestinal tract, and after absorption from the intestine, metabolite 2 was converted into metabolite 1 through methylation by COMT in the liver, and arctiin and tracheloside existed as metabolite 1, the genuine genin, in the blood stream.