Defective platelet aggregation induced by platelet activating factor in myeloproliferative disorders: deficiency of an aspirin-independent mechanism?

Platelets from 6 out of 10 patients with myeloproliferative disorders showed only a single reversible wave of aggregation when challenged with platelet activating factor (PAF). Preexposure to subthreshold concentrations of adrenaline resulted in a full irreversible response to PAF. Aspirin, however, removed this synergism. In the remaining 4 patients, PAF induced a full response but aspirin abolished the synergism with adrenaline in 2 of them. In platelets from all controls aspirin failed to abolish the synergism between PAF and adrenaline. It is suggested that patients with myeloproliferative disorders lack - to varying degrees - an aspirin-independent mechanism which amplifies the primary response to PAF. Such a mechanism could involve the products of arachidonic acid metabolism catalyzed by lipoxygenase.