Metabolism of magnolol from Magnoliae Cortex. II. Absorption, metabolism and excretion of (ring-14C)magnolol in rats.

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Abstract
After single oral administration of [ring-14C]magnolol, a central nervous system-depressive, muscle-relaxant and bactericidal principle of Magnoliae Cortex to rats, the blood levels of radioactivity showed two peaks at 15 min and 8 h, suggesting an enterohepatic circulation of magnolol and its metabolites. The radioactivity was distributed mostly in the gastrointestinal tract and liver, and next in the kidney, pancreas and lung. A major metabolite excreted in the bile was [ring-14C]magnolol-2-O-glucuronide. After oral and intraperitoneal administration of [ring-14C]magnolol, most of the radioactivity was eliminated into the feces and urine within the first 12 h in either case. The oral doses was recovered to a greater extent from the feces (72% of the administered radioactivity) than from the urine (7.4%) in 144h, and the intraperitoneal dosage was similarly recovered from the feces (67%) and from the urine (12%). On repeated oral administration of cold and [ring-14C]magnolol, the composition of the fecal metabolites significantly changed, and tetrahydromagnolol, 5-((E)-1-propenyl)-5''-propyl-2,2''-dihydroxybiphenyl, 5-allyl-5-propyl-2,2''-dihydroxybiphenyl, isomagnolol and 5-allyl-5''-((E)-1-propenyl)-2,2''-dihydroxybiphenyl were detected.