Octylonium bromide, an antagonist of platelet-activating factor.

Octylonium bromide, a spasmolytic agent in clinical use for the treatment of increased tone and/or motility of the gastrointestinal tract, was examined for its ability to antagonize some biological actions of platelet-activating factor. It was found capable of inhibiting, in a concentration- or dose-dependent fashion, the platelet-activating factor-induced platelet aggregation of rabbit platelet-rich plasma, bronchoconstriction in guinea-pigs, hypotension in rats and lethality in mice, its potency being between 1/15 and 1/50 that of WEB 2086. On the other hand, octylonium bromide was not capable of inhibiting the platelet-activating factor-induced contraction of guinea-pig lung parenchymal strips, an effect which is inhibited by WEB 2086 only at high concentrations. It is worth mentioning that octylonium bromide antagonized endotoxin-induced gastrointestinal damage, known to be due to platelet-activating factor release, at doses comparable to those which exert a spasmolytic effect in man. The role of platelet-activating factor in human gastrointestinal disorders has not yet been clearly established and, therefore, the clinical implications of this property of octylonium bromide are at the moment unknown.