Studies on chromatin. II. Effects of carcinogens and hormones on rat liver chromatin.

Nuclei were isolated from rat liver during the prolonged feeding of the 2 carcinogens, N-hydroxy^-acetylaminofluorene and 3'-methyl-4-dimethylaminoazobenzene, and during the pro longed feeding of the noncarcinogen, 2-methyl-4-dimethylaminoazobenzene. Nuclei were also isolated from rat liver tumors induced by the above carcinogens. Chromatin was isolated from these nuclei and analyzed for RNA, total protein, and histone protein content. The 2 carcinogenic diets caused an initial de crease in the RNA content of liver chromatin, while in the re sultant tumors the RNA content of chromatin was greatly increased. Total protein content of chromatin from the animals fed the carcinogens also showed significant variations from normal. Neither the RNA nor the total protein content of chromatin from animals fed 2-methyl-4-dimethylaminoazobenzene differed from normal. No significant changes were observed in the histone protein content of chromatin from any animals. In short-term experiments, A7-hydroxy-2-acetylaminofluorene, 3'-methyl-4-dimethylaminoazobenzene, and the carcinogen, aflatoxin Bi, all caused a drop in the RNA content of the nu cleus; 2-methyl-4-dimethylaminoazobenzene did not lower nu clear RNA content. Intense stimulation of the liver by pituitary hormones in creased the RNA and total protein (but not the histone protein) content of liver chromatin.