Stimulation of endothelial cell proliferation by platelets.

Endothelial cell proliferation in a 72-hour period is shown either stimulated by an increasing number of nonactivated platelets (●) or by thrombin-activated (0.5 U/mL) platelets (▵). Error bars represent the SEM. A 2-fold increase in endothelial cell number, as measured by the MTT assay, was found for both activated and nonactivated platelets.