Time- and pH-dependent release of PDGF and TGF-β from platelets in vitro

We studied the spontaneous and thrombin-induced activation of platelets and their release of platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) at different pH values. Platelet activation was assayed with anti-bodies against P-selectin and performed in serum-free media. The release of PDGF and TGF-beta was determined by ELISA after 15 min and 12 h. There was no activation at pH 5.0, while a time- dependent release of growth factors occurred at neutral and alkaline pH. The results suggest that release of growth factors is not only dependent on platelet activation but also on incubation time and pH. Although the used serum-free experimental situation is different from normal conditions for platelets in vivo, the findings of a late release of growth factors may, nevertheless, be relevant to wound healing.