[The effect of growth factors on cell cultures]

As sources for cell growth factors with polypeptide nature sera, organs and conditioned culture media can be used. A few samples of such factors are listed in this report. Their main effects on cultured cells consist in the stimulation of DNA-synthesis and proliferation. The knowledge on the mechanism of action of these factors is still incomplete. Some aspects of this question are discussed. The development of chemically defined culture media will be a fundamental prerequisite for further progress in the elucidation of the problems of growth regulation on the cellular level. Certain discrepancies between the effects of the growth factors in vivo and in vitro might arise by the fact that the cells in culture are not provided by adequate substrata when growing on glass or plastic and thus having a cell shape not typical for the in vivo situation. The cell shape may have an influence on the mitogenic response of the cells.