Isolation of a bronchodilator flavonoid from the Thai medicinal plant Clerodendrum petasites

The ethanolic extract of Clerodendrum petasites was tested to evaluate the spasmolytic, activity on isolated guinea-pig tracheal smooth muscle. The crude extract (2.25-9.0 mg/ml) dose-dependently caused relaxation of tracheal smooth muscle which was contracted by exposure to histamine. A bioassay-guided fractionation of the crude extract was performed by means of partitioning and centrifugal partition chromatography. Finally the active principle was isolated and identified as the flavonoid hispidulin (EC50: (3.0 +/- 0.8) x 10(-5) M). These results suggest that hispidulin may be beneficial in the treatment of asthma. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.