Wc. Ko et al., Relaxant effects of petasins in isolated guinea pig trachea and their structure-activity relationships, PLANTA MED, 66(7), 2000, pp. 650-652
In the present study, we attempted to compare four petasins, isolated from
Petasites formosanus Kitamura, and to look for structure-activity relations
hips, which may be helpful for synthesizing more active compounds for the t
reatment of asthma. Four petasins, including petasin, isopetasin, S-petasin
and S-isopetasin, concentration-dependently relaxed histamine (10 muM)-, c
arbachol (0.2 muM)-, KCI (30 mM)-, and leukotriene D-4 (10 nM)-induced prec
ontractions of isolated guinea pig tracheais. The IC50 Values strongly show
ed that the relaxant effects of the sulfur-containing petasins, S-petasin a
nd S-isopetasin, were more potent than those of non-sulfur-containing petas
ins, petasin and isopetasin. S-Isopetasin, with IC50 Values around 10 muM,
selectively relaxed carbachol- and KCI-induced precontractions, and had alm
ost no effects (IC(50)s > 300 muM) on histamine- and leukotriene D-4-induce
d precontractions. However, 5-petasin, with IC50 values about 6 -9 muM, non
-selectively relaxed the precontractions induced by all these contractile a
gents. The influence of isomerization of either petasin to isopetasin or S-
petasin to S-isopetasin on the relaxant effects is not clear.