Antagonism of platelet-activating factor (PAF)
The ginkgolides, and in particular ginkgolide B, are known antagonists of PAF
(69–73). PAF is a potent inducer of platelet aggregation, neutrophil degranulation,
and oxygen radical production leading to increased microvascular permeability
and bronchoconstriction. Intravenous injections of PAF induced
transient thrombocytopenia in guinea-pigs, which was accompanied by nonhistamine-
dependent bronchospasm (69, 70). Ginkgolide B has been shown to
be a potent inhibitor of PAF-induced thrombocytopenia and bronchoconstriction
(71, 72). PAF or ovalbumin-induced bronchoconstriction in sensitized
guinea-pigs was inhibited by an intravenous injection of ginkgolide B (1–3mg/
kg) 5 minutes prior to challenge (73).