Effects of the extract of the bark of Magnolia obovata and its biphenolic constituents magnolol and honokiol on histamine release from peritoneal mast cells in rats

We have previously reported that salboku-to, an Oriental herbal remedy comp osed of a mixture of 10 different herbal extracts, possesses anti-histamine release effect on mast cells in rats. This effect may be due mainly to the extract of the bark of Magnolia obovata (M. obovata), a constituent herb o f saiboku-to. In the present study, it was demonstrated that the bark extra ct inhibited compound 48/80 (C48/80)-induced histamine release from mast ce lls in a concentration-dependent manner (50% inhibitory concentration, IC50 = 56.98 mug/ml). Furthermore, the inhibitory activity was found in the met hanol fraction, but not in water and 50% aqueous methanol fractions derived from the bark extract. Magnolol and honokiol isolated from the methanol fr action inhibited C48/80-Induced histamine release from mast cells. The pote ncy of magnolol (IC50 = 1.04 mug/ml) was greater than that of honokiol (IC5 0 = 2.77 mug/ ml). Furthermore, the actual amount of magnolol (49.76 +/- 1. 14 mg) contained in the bark of M. obovata (5 g) was greater than that (8.5 8 +/- 0.19 mg) of honokiol. Taken together, the present results suggest tha t magnolol may be responsible for the biological efficacy of the bark extra ct of M. obovato.