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Incorporation of Radioactive Phosphate into Nucleic Acids of Regenerating Rat Liver^*

( McArdle Memorial Laboratory, Medical School, University of Wisconsin, Madison 6, Wis.)

1. In rats subjected to partial hepatectomy there was very little incorporation of P³² into the deoxyribonucleic acid (DNA) of the liver during the first 12 hours after the operation.

2. The most active incorporation of P³² into DNA of regenerating liver was found 20–24 hours after partial hepatectomy.

3. When P³² was injected 20 hours after the operation, the DNA of the liver reached its maximum specific activity about 20 hours later.

4. P³² was more actively incorporated into the ribonucleic acid (RNA) of the nucleus and of the various cytoplasmic fractions in regenerating liver than in resting liver. However, the relative order of the specific activities of the various RNA fractions was the same in both tissues.

5. Changes in the absolute amounts of liver constitutents during the regenerative period have been recorded. The observed increases in total RNA, DNA, and number of nuclei per liver were roughly proportional to the increase in liver weight. The amount of DNA per nucleus showed no consistent change with time.

6. The synthesis of DNA, as calculated from the P³² incorporation, has been compared with the net increase in DNA of regenerating livers. The good agreement between the calculated and measured values indicates that the synthesis of DNA is irreversible.

^* This work was supported by grants from the Alexander and Margaret Stewart Trust Fund, from the American Cancer Society Institutional Grant No. 71A, and from the Jonathan Bowman Memorial Fund.

Received 8/16/54.