Molecular Mechanisms of Liver Regeneration

V. THE EFFECT OF X-RADIATION ON THE INCORPORATION OF ¹⁴C-OROTIC ACID INTO RAPIDLY LABELED NUCLEAR RIBONUCLEIC ACID

From the ¹ From the Department of Pathology and Regional Primate Center, University of Wisconsin, Madison 6, Wisconsin

Rapidly labeled nuclear ribonucleic acid was extracted with phenol from normal and regenerating livers after ¹⁴C-orotic acid injection. Highest specific activities were obtained 20 min after the injection of the precursor. When bentonite was used in the phenol extraction, the distribution of the radioactivity in the sedimentation profiles of the rapidly labeled nuclear RNA was modified. In presence of bentonite, the peak of radioactivity precedes the ultraviolet absorption peak of the RNA of highest molecular weight. After partial hepatectomy, the specific activity of the phenol-extracted, rapidly labeled nuclear RNA increases between 0 and 6 hours and 12 and 24 hours, but remains unchanged between 6 and 12 hours after operation. The increase in specific activity is caused by an increase in the labeling of the RNA of highest molecular weight.

Whole body doses of x-radiation administered 6 hours prior to killing the experimental animals interfere with the incorporation of ¹⁴C-orotic acid in the rapidly labeled nuclear RNA extracted from liver obtained 6, 12, 18, and 24 hours after partial hepatectomy. The effect of x-radiation is more marked 18 and 24 hours than 6 and 12 hours after partial hepatectomy. Irradiation is without effect on the incorporation of ¹⁴C-orotic acid into the rapidly labeled nuclear RNA extracted from normal livers. In normal or regenerating liver, x-irradiation does not modify the ultraviolet absorption profiles of the phenol-extracted, rapidly labeled nuclear RNA.

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