PLATELET EFFECTS ON TISSUE FACTOR AND FIBRINOLYTIC INHIBITION OF CULTURED HUMAN-FIBROBLASTS AND VASCULAR CELLS

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 60  (1) , 140-147
Abstract
Platelets stimulate tissue factor, the initiator of the extrinsic coagulation pathway and increase fibrinolytic inhibition in fibroblasts grown in vitro. Cellular tissue factor increased an average of 2.8-fold over the control levels after a 6-h incubation with platelets and no activity was present in the media. Fibrinolytic inhibition was stimulated in both the fibroblasts and their media in the presence of platelets and accumulated throughout a 24-h incubation. Neither leukocytes nor erythrocytes stimulated these changes. Both tissue factor and fibrinolytic inhibition increases were dependent on platelet concentration and were blocked by inhibitors of RNA or protein synthesis. Control smooth muscle cells had higher tissue factor and fibrinolytic inhibition than fibroblasts, but their response to the presence of platelets was similar. Confluent monolayers of endothelial cells had very low levels of tissue factor that were not altered by the presence of platelets. The ability of endothelial cells to inhibit fibrinolysis was enhanced by the presence of platelets. The fraction that stimulated tissue factor and fibrinolytic inhibition was distinct from platelet-derived growth factor and from the fraction that enhanced leukocyte tissue factor. It was associated with an insoluble, nonmitogenic fraction that was not inactivated by phospholipase C or diisopropylfluorophosphate, nor was it chloroform:methanol extractable. Platelets are a physiologic modulator for both cellular tissue factor and the fibrinolytic system in vitro.