Serum dependent growth of primary cultured differentiated fetal rat hepatocytes in arginine‐deficient medium

Fetal rat hepatocytes in primary monolayer cultures multiply in arginine‐deficient medium. Both the “recovery efficiency” and the final cell density of the cultured cells are proportional to the concentration (0–15%, v/v) of dialyzed fetal bovine serum in the medium. Stationary‐phase cells divide again following addition of fresh serum to the culture. After two to three generations of growth, the chromosome number of these cells remains diploid [2N = 42]. Cross‐feeding (of a subpopulation of arginine‐requiring liver‐derived cells by parenchymal arginine‐synthesizing cells) and cellular degradation of various serum proteins do not account for sources of arginine required for cell multiplication in this culture system. Because these cultured hepatocytes utilize ornithine for arginine biosynthesis, and because ornithine enhances the rate and the amount of cell multiplication, it is more likely that the multiplying cells are parenchymal arginine‐synthesizing hepatocytes. At least two classes of serum factors are required for the growth of cultured fetal rat hepatocytes: one stimulates cell multiplication; the other is required for cellular survival and/or attachment to the culture dish. These factors have been partially separated by fractionation with ammonium sulfate; they are non‐dialyzable, heat labile, and sensitive to changes in pH.