DNA synthesis in sham-operated and 40% hepatectomized rats after the i.p. injection of rat liver cytosol. DNA synthesis in the liver was determined as described under “Materials and Methods.” ■, sham-operated rats given injections of PBS; ■, 40% hepatectomy plus PBS; □, 40% hepatectomy plus cytosol from normal rat liver; ■, 40% hepatectomy plus cytosol from 24-h regenerating rat liver; □, 40% hepatectomy plus cytosol from weanling rat liver. Columms, means from 20 rats; bars, SD. *, significantly different from the control value (P <0.05).