Role of platelet-activating factor in aggregation of leukocytes and platelets in cerebral ischemia.

Leukocyte and platelet aggregation stimulated with formyl-methionyl-leucyl-phenylalanine (FMLP) was measured in 32 patients with cerebral ischemia and in 15 controls, using a whole blood aggregometer. The increases in impedance and the reductions in leukocyte and platelet counts were significantly greater in stroke patients than in controls. Aggregation was inhibited by oral ticlopidine, but not by oral aspirin. The effects were clearly counteracted by platelet-activating factor (PAF) antagonists, and counteracted in part by a 5-lipoxygenase inhibitor. The results suggest that platelets tend to be activated by PAF and leukotrienes liberated from hyperaggregable leukocytes in patients with ischemic stroke.