Studies on the biotransformation of paeonol by isotope tracer techniques. II. Species differences in metabolism.

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Abstract
Species differences in the metabolism of paeonol (2-hydroxy-4-methoxyacetophenone: I) [Paeonia moutan] in mice, rats, guinea pigs and rabbits were studied by the RI (radioisotope) tracer technique. After the administration of a single dose of 20 mg (6-70 .mu.Ci)/kg paeonol[carbonyl-14C] (I-14C), radioactive metabolites excreted in the urine were analyzed. The excretion of I-14C was rapid in all species; > 83-98% of administered radioactivity was excreted in the urine and feces during 2 days after the administration. The 14C-activity excreted in feces was 10.6% in mice, 4.7% in rats, 2.9% in guinea pigs and 0.8% in rabbits. The urine is the major excretion route in all species. 2,5-Dihydroxy-4-methoxyacetophenone (II), resacetophenone (III) and unchanged I were detected in all species as urinary metabolites. The metabolites were found as the free form, .beta.-glucuronide, sulfate and enzyme-resistant conjugate. The major metabolite in each species was as follows: mice, II 43.1%; rats, II 62.0%; guinea pigs, III 58.1%; rabbits, III 42.7% and II 42.2%. All metabolites were conjugated in rats while the total amount of unconjugated metabolites was 50-60% of total metabolites in other species. .beta.-Glucuronide and sulfate in rats accounted for 19.9 and 8.2%, respectively. Only small amounts of these conjugated forms were excreted in other species. Enzyme-resistant conjugate accounted for 60.2% in rats, but only 35-43% in other species.