The present studies were designed to determine the incorporation of radioactive precursor into tumor and hepatic RNA in solid tumor of rats. The animal used in these, experiments were female rats, weighing 100-120 gm. The Walker 256 carcinosarcoma was transplanted 12 days prior to the experiment. The orotic acid 6C^14 was injected intravenously in a dose of 3.3,?c/200gm. of body weight. At 15min. and 60min. after the injection of radioactive eroticacid the rats were sacrificed and the liver and tumor tissues were excised. By the differential centrifugation, the nuclear, mitochondrial, microsomal and supernatant fractions were fractionated. The RNA of the various cellular componenets were fractionated with phenol and buffer to give phenol extractable RNA (p-RNA) and a residual RNA (r-RNA) which remained in thephenol phase. The radioactivity of p-RNA and r-RNA of each cellular fractions were determined in windowless :gas´ flow counter. The RNA was assayed-by ordinal method and, the specificactivity were calculated.
The results obtained were. as follows:
1. The specific activity of r-RNA in all cellular fractions of the rat liver were markedly,hig compared to p-RNA.. The maximum incorportion was found at 30min. after the injection of.: radioactive orotic acid in both nuclear p-RNA and r-RNA and at 60min. in all cellular fraction except nuclear
2 Although the incorporation, rate of radioactive orotic acid into, the nuclear and mitochondria)RNA of Walker tum9r"was unchanged -compared to liver microsomal incorporation rate .was increased 1. 7, times at 15min., 2.3. times at, 30min., 1.3 times at 60min. and supernatant fraction was increased 2.2 times at 15min., 1.7 times at 60min. after the injection of oroticacid.
3. The incorpioration of radioactive orotic acid into the nuclear r-RNA of Walker tumor was, increased 2.6 times at 15min., 2.1 times at 30min. and 2.6 times at 60min., and . the, mitochondrial incorporation rate was. increased 1.5 times, at 15 min., 1.8 times -at 30min.,. 1. Fr times at,_ 60min. compared -with hepatic r-RNA.
The incorporation rate of radioactive orotic -acid into the microsomal and supernatant r-RNA were not changed.
4. It was shown that increased incorporation of labeled orotic acid into p-RNA of microsomal and supernatant and into the r-RNA of nuclear and mitochondria fractions were caused by essential and excessive biosynthesis of protein in rapid growing neoplastic tissues.
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