Biosynthesis of nuclear RNAs during 3'-methyl-4-dimethyl-aminoazobenzene hepatocarcinogenesis and in transplantable rat hepatomas.

: The long-term administration of 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) to rats causes marked changes in concentrations and synthesis of nucleic acids in the liver. In the beginning, a decrease in total cellular RNA concentration can be seen. On the other hand, at the stage of tumor onset the concentration of nuclear RNAs in precancerous lesions and hepatomas is elevated. Incorporation of 3H-orotic acid into nuclear RNA after 45 min of in vivo labeling serving as a measure of biosynthesis of nuclear RNAs is markedly decreased when compared to control livers. This decrease takes place from the very beginning of the process and goes on until primary hepatomas arise in which its values are approximately at 10% of those observed in controls. In the present study the problem of the increase of proliferative activity at early stages of carcinogenesis is discussed which is not in correlation with the changes in nuclear RNA biosynthesis.