Time- and pH-dependent release of PDGF and TGF-beta 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 antibodies against P-selectin and performed in serum-free media. The release of PDGF and TGF-beta was determined by ELISA after 15 min and 12h. 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 o f 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.