Effect of saikosaponin-A, a triterpenoid glycoside, isolated from Bupleurum falcatum on experimental allergic asthma.

The separation and isolation of an extract of Bupleurum falcatum were performed based on antiallergic activities in preliminary studies with higher plants. The final active compound was identified as saikosaponin-A (SSA), a triterpenoid glycoside. SSA at more than 1 mg/kg (i.v.) significantly inhibited the passive cutaneous anaphylaxis reaction in rats in a dose-dependent manner, attaining a maximum inhibition of approximately 60% with 10 mg/kg. SSA at 3 and 10 mg/kg also suppressed asthmatic bronchoconstriction in sensitized guinea-pigs. SSA possesses a weak inhibitory activity on histamine-induced tracheal contraction in guinea-pigs and on histamine release induced by A-23187 in rat mast cells. These results indicate that SSA has an inhibitory activity against allergic asthma. This activity seems to derive from both antagonism of the histamine action and inhibition of allergic mediators. Additional mechanisms may also be involved.