Platelet MPs mediate the proangiogenic effect. (A) The proangiogenic effect of conditioned medium from EPC cultures decreased over time, arguing against an outgrowth of a progenitor cell population. (B) The depletion of MPs from the conditioned medium (C/M-MPs) of EPC cultures reduced endothelial tube formation in the Matrigel assay. (C) The addition of the disintegrin echistatin and the inhibitory peptide GPIIIa-4 against the platelet integrin αIIb attenuated the proangiogenic effect of the conditioned medium in the presence of platelet MPs (C/M + MPs). *P < .05 level; **P < .01. Results were obtained in 3 independent experiments.