[Thermolabile inhibiting proliferation of connective tissue cell activity from platelets]

The action of a platelet extract (PE) and a heat-inactivated PE on 3T3 cells proliferation has been investigated. The heat-inactivated PE and platelet poor plasma (PPP) together can promote cell proliferation like fetal calf serum. At the same time PE inhibits proliferation of the cell culture stimulated by 5% fetal calf serum, whereas the heat-inactivated PE does not. Although the actions of 2% PE and 2% heat-inactivated PE on the cells incubated with PPP are equal, the stimulating effect of a 10% heat-inactivated PE is higher than that of a 10% PE. Thus, the inhibitor acts only at high concentrations. The role of the platelet-derived inhibitor in the limiting of extensive cell proliferation during vessel wall injury repair is discussed.