[Concentration and characterization of a liver cell proliferation factor from partially hepatectomized rat livers...

An extract of rat liver, made 12 h after partial hepatectomy, was injected into untreated rats. The synthesis of DNA in the liver cells of the injected animals showed a 3.3 fold increase in comparison with controls. A similar increase was observed in the mitosis index. Injection of liver extracts from normal rats showed no effect when compared with the injection of NaCl. The effect of the active extract was not altered by neuraminidase treatment. Trypsin-chymotrypsin treatment, howerver, removes the activity. The active factor must therefore be either a protein or a protein-like substance. The molecular weight of the factor was shown to be between about 30 000 and 50 000 by molecular filtration. The specific activity after molecular filtration was raised by a factor of 100. The factor is inert with respect to the proliferation of kidney and spleen. It is apparently not species-specific, however, since it also causes increased proliferation of liver cells in normal mice.