The ethnomedicinal uses of the aqueous leaf extract of
Andrographis paniculata
Nees (AP) include treatment of pain and inflammation, malaria, asthma and common cold. We designed this study to characterize some effects of AP and those of its andrographolide constituent. Guinea pig tracheal rings suspended in organ baths containing PSS were precontracted with histamine or carbachol and then exposed to cumulative concentrations of AP, andographolide or theophylline. The effect of AP was tested in Ca
2+-depleted tracheal rings stimulated with the EC
50 of histamine in Ca
2+-free PSS. IC
50 and E
max values were calculated for each relaxant. Results showed that both AP and andrographolide possessed relaxant effects on the tracheal smooth muscle. While AP was more effective on histamine-induced contraction, andrographolide and theophylline were more effective on carbachol-induced contraction. The IC
50 values of andrographolide were significantly (p< 0.05) higher than those of theophylline in the two contractile agents. The presence of AP significantly (p< 0.0001) attenuated the contractile force produced by 6.4 x 10
-3 M Ca
2+ in Ca
2+-depleted rings. It is concluded that andographolide contributes at least in part to the relaxant action of AP on tracheal smooth muscles. The mechanism of action is related to inhibition of Ca
2+ influx into tracheal smooth muscle cells.
