Histochemical correlation between glycogen, nucleic acids and nucleases in pre-neoplastic and neoplastic lesions of rat liver after short-term administration of N-nitrosomorpholine

Abstract

After 7 weeks of oral administration of the carcinogen N-nitrosomorpholine (12 mg NNM ad 100 ml of drinking water) to male rats, marked hepatocellular changes were found predominantly in the centers of the lobules. These were loss of glycogen, disorganisation of the basophilic bodies and, sometimes, loss of cytoplasmic basophilia or pyroninophilia, necrotic cells and increase in the activity of acid DNAse and RNAse. These centrilobular alterations were reversible after withdrawal of the carcinogen. They are, therefore, attributed to the nonspecific-toxic effect of the carcinogen. In peripheral and midzonal regions of the lobules basically different cellular changes appeared which were unimportant during the phase of intoxication, but became prominent after cessation of the carcinogenic treatment. These lesions were: excessive storage of glycogen, displacement of basophilic bodies and an increase in cytoplasmic acidophilia. The hepatocytes showing these cytoplasmic changes initially formed foci. Neoplastic nodules and frank hepatocellular carcinomas developed later. During these later stages of the experiment both the foci and the nodules consisted of 4 main types of altered hepatocytes: 1) "clear" glycogen storage cells, 2) acidophilic cells, 3) vacuolated (fat storing) cells, 4) basophilic (pyroninophilic) cells poor in, or free from, glycogen. The larger nodules and carcinomas contained predominantly basophilic cells. The activity of nucleases, especially that of acid DNAse, decreased in small foci which as a rule developed later than the foci of glycogen storage. In most cells of neoplastic nodules and carcinomas the activity of these enzymes disappeared, but it reappeared in necrotic cells. The progressive alterations in the activity of the nucleases seemed to be related to the phenotypic expression of malignancy and could be a sign of a fundamental metabolic change taking place during a relatively late step in the malignant transformation.