[Effect of cytoplasmic and serum factors on the uptake of (3H) thymidine-triphosphate (TTP) by isolated nuclei of liver cells].

The actions of cytoplasm (ultracentrifuged supernatant 105 000 times g) and of serum on the DNA synthesis (uptake of (3H) TTP) by isolated nuclei of liver cells were studied. Cytoplasm from liver cells obtained at various intervals after partial hepatectomy revealed a variable effect only with isolated nuclei of liver cells from partially hepatectomized rats. Cytoplasm obtained from liver cells eight hours after partial hepatectomy failed to show the usual inhibitory effect. Presumably the inhibitory substances normally present in cytoplasm are inactivated within a certain time after partial hepatectomy. Serum of partially hepatectomized animals enhanced the uptake of (3H) TTP by nuclei of normal liver cells and those from partially hepatectomized animals. The stimulating effect was present only in the serum obtained between four and twelve hours after partial hepatectomy. It remains unclear whether the effects described are growth factors specific for the liver.