Differential effects of inhibitors of cell division upon the growth stimulating activities of insulin and serum in nutritionally depleted human and mouse cells.

Cultured mouse and human cells were arrested in their growth by artificially depriving them of phosphate. The quiescent cells could be stimulated to synthesize DNA and to divide by addition to the growth medium of insulin, dialyzed serum and/or the full concentration of phosphate. In order to gain insight into mechanisms by which insulin and serum stimulate growth, the inhibitory effects of antimitotic agents were examined. Of the inhibitors tested, vinblastine and cytocalasin B abolished the growth promoting activity of insulin, while colchicine inhibited the activity of both serum and insulin. The present results suggest that insulin-stimulated growth is meciated by a different path way than serum-stimulated growth and is sensitive to mechanisms that occur at various times prior to insulin addition.