Effects of hepatocarcinogens on the synthesis and content of rat liver nuclear RNA.

and thioacetamide caused similar changes in the nuclear RNA metabolism of precancerous rat liver, and whether these changes could be distinguished from those caused by the weak hcpatocarcinogen 4'-methyl-4-dimethylaminoazobenzene (4'Me-DAB). Carcinogens were administered by intraabdominal injection or by feeding in semisynthetic diets. Their effects on nuclear RNA synthesis and nuclear RNA concentration were compared 5 days after injection or after 2, 4, and 6 weeks of feeding. Nuclei were purified and the RNA fractionated into a slowly labeling non-nucleolar nuclear (NNN) RNA fraction and a more rapidly labeling nucleolar fraction. Synthesis of RNA in these subfractions was determined by incorporation of orotic acid-6-14C and adenine-8-14C. When injected: (a) 3'-Me-DAB decreased incorporation of orotic acid-6-14C into