Platelets as a source of fibroblast growth-promoting activity

Evidence is presented that platelets are an enriched source of growth-promoting activity for 3T3 cells, an established line of mouse fibroblasts. Rat or human serum stimulates 3T3 cell growth more than autologous plasma; this increased activity is at least partly due to the release of a growth-promoting activity from platelets disrupted during the clotting process. Platelet extract stimulation of 3T3 cell growth is approx. 5 times greater than an equal amount of autologous serum. This platelet growth activity is (1) pH-stable; (2) pepsin-labile; (3) heat-stable at 56 °C; (4) non-dialysable, and (5) similar in size to the serum 3T3 growth-promoting molecule. 3T3 cells transformed by Simian virus 40 show an equivalent stimulation by the platelet solution and serum.