EFFECTS OF BAICALEIN ON PROSTANOID GENERATION FROM THE LUNG AND CONTRACTILE RESPONSES OF THE TRACHEA IN GUINEA-PIG

Effects of baicalein on release of slow reacting substance of anaphyla xis (SRS-A) or leukotriene (LT) from the sensitized guinea pig lung af ter antigen challenge and tonus of guinea pig tracheal muscles were st udied. Baicalein inhibited release of SRS-A from sensitized guinea pig lung after antigen challenge. High-performance liquid chromatography (HPLC) analysis revealed that released SRS-A consisted of LTC4 and D-4 . Baicalein also reduced release of LTC4 and D-4 from the sensitized l ung after antigen challenge. Baicalein relaxed the isolated guinea pig tracheal smooth muscle contracted by LTD4, carbachol or histamine. Ho wever, this compound produced a contraction when the tracheal muscle w as contracted by prostaglandin F-2 alpha(PGF(2 alpha)). This contracti on by baicalein was abolished by pretreatment with indomethacin, a cyc looxygenase inhibitor. Baicalein elicited a relaxation in the normal n on-sensitized tracheal preparation but a contraction in the tissue iso lated from actively sensitized guinea pig in 4 among 7 cases. Baicalei n also produced a contraction in the trachea pretreated with phorbol d ibutyrate and contracted by carbachol, which was eliminated after trea tment with indomethacin. The results suggest that baicalein exerts act ion via, at least, two different mechanisms, the inhibition of releasi ng SRS-A (LTs) and direct relaxing effects on the trachea. Besides, ba icalein seems to produce contraction under certain conditions, which m ay involve stimulation of the cyclooxygenase pathway.