An antagonistic activity of etizolam on platelet-activating factor(PAF). In vitro effects on platelet aggregation and PAF receptor binding.

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Abstract
The antagonistic effect of etizolam, an anti-anxiety drug, on platelet-activating factor (PAF) was investigated in rabbit platelets in vitro. Etizolam inhibited PAF-induced aggregation in a dose-dependent manner, with an IC50 of 3.8 .mu.M, about one tenth that of triazolam (IC50=30 .mu.M). At 300 .mu.M, it inhibited both ADP and arachidonic acid-induced aggregation only slightly, while the other anti-anxiety drugs tested had no effect on PAF-induced aggregation even at this concentration. Etizolam and triazolam inhibited the specific binding of 3H-PAF to PAF receptor sites on washed rabbit platelets with IC50 values of 22 nM and 320 nM, repectively. Diazepam and estazolam were inactive even at 1 .mu.M. These results indicate that etizolam is a specific antagonist of PAF.