Insulin as a Potent, Specific Growth Factor in a Rat Hepatoma Cell Line

A line of rat hepatoma cells in culture which, in response to serum starvation, become arrested in the early G$_{1}$ phase of growth, can be stimulated by insulin alone to enter the cell cycle and traverse S phase. A half-maximum response is observed at 30 to 70 picomolar concentrations and the maximum response is essentially identical to that found with optimum serum concentrations.