Pharmacokinetics, Bioavailability, and Tissue Distribution of Magnolol Following Single and Repeated Dosing of Magnolol to Rats

Magnolol (M) is a polyphenol antioxidant abundant in the bark of Magnolia officinalis Rehder & E. Wilson, a popular Chinese herb. To understand the pharmacokinetics and bioavailability of M, Sprague-Dawley rats were intravenously injected with a bolus of M (20 mg/kg) and orally given a single dose and seven doses of M (50 mg/kg). Blood samples were withdrawn via cardiopuncture at specific times. Organs including the liver, kidney, brain, lung, and heart were collected at 30 min after the 7th oral dose. The serum and tissue specimens were assayed by HPLC before and after hydrolysis with β-glucuronidase and sulfatase. The results showed that after intravenous bolus, the systemic exposure of magnolol glucuronides (MG) was comparable with that of M while after oral administration, magnolol sulfates/glucuronides (M S/G) were predominant in the bloodstream. Conversely, M was predominant in the liver, kidney, brain, lung, and heart. Among the studied organs, the liver contained the highest concentrations of M and MG. In conclusion, M S/G was the major form in circulation, whereas M was predominant in the liver, kidney, brain, lung, and heart after oral administration of M; among these organs, the liver contained the highest concentrations of M and MG.