Summary
The effects of platelet-activating factor (PAF) on in vivo platelet aggregation were
studied in anaesthetized beagle dogs by using the extracorporeal filter-loop technique.
Intraarterial administration of PAF caused an immediate increase in filter pressure,
indicating enhanced in vivo platelet aggregation. Intravenous administration of PAF
(3-100 ng kg−1) resulted in a transient dose-dependent inhibition of spontaneous platelet aggregation
on the filter with concomitant elevation in plasma 6-keto-PGF1Α levels. These changes were significantly attenuated by pretreatment of the animals
either with BN 52021 (4 mg kg−1), a specific PAF receptor antagonist or with acetylsalicylic acid (25 mg kg−1). Intraarterial infusion of exogenous prostacyclin at concentrations similar to those
observed following intravenous PAF administration, resulted in a transient inhibition
of the spontaneous platelet aggregation. These data provide evidence for prostacyclin
release in response to PAF, and suggest that prostacyclin may mediate the in vivo
anti-aggregatory action of PAF in anaesthetized dogs.
