IN-VITRO RELEASE OF VASCULAR ENDOTHELIAL GROWTH-FACTOR DURING PLATELET-AGGREGATION

Platelet aggregation is a cardinal feature of both vascular repair and vascular disease. During aggregation platelets release a variety of v asoactive substances; some of these promote angiogenesis, endothelial permeability, and endothelial growth, actions shared by vascular endot helial growth factor (VEGF). This study was undertaken to investigate the hypothesis that VEGF is released by aggregating platelets. We foun d that VEGF was secreted during the in vitro aggregation of platelet-r ich plasma induced by thrombin, collagen, epinephrine, and ADP (range 23-518 pg VEGF/ml). Furthermore, serum VEGF levels were elevated compa red with plasma (230 +/- 63 vs. 38 +/- 8 pg VEGF/ml), indicative of VE GF release during whole blood coagulation. Lysates of apheresed, leuko cyte-poor platelet units contained significant amounts of VEGF (2.4 +/ - 0.8 pg VEGF/mg protein). VEGF message and protein were also present in a megakaryocytic cell line (Dami cell). These results suggest const itutive roles for platelet VEGF in the repair of intimal vessel injury and in the altered permeability and intimal proliferation seen at sit es of platelet aggregation and thrombosis.