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The histochemical demonstration of polycytidylic acid and polyuridylic acid hydrolases in rat liver during azo dye carcinogenesis.

Films of polycytidylic acid (poly-C) and polyundylic acid (poly-U) were exposed to liver sections from rats fed a control or a hepatocarcinogenic diet, and the results were compared with those obtained with films of ribonucleic acid. The livers from rats fed the basal control diet showed a distribution of poly-C and poly-U hydrolase activities comparable to that observed in normal tissue whereas they exhibited a significant increase in centrilobular ribonuclease activity. In livers of 4-dimethylaminoazobenzene-fed rats, the centnlobular necrotic tissue was negative to poly-C and strongly positive to poly-U and ribonucleic acid. The regenerating parenchyma gave positive reactions with the different substrates but areas of the hyperplastic tissue became deficient in all three hydrolase activities after 8 weeks of azo dye feeding. The hyperbasophilic foci that developed a few weeks later were inactive against poly-C, poly-U and ribonucleic acid, and so were the hepatomas except for the necrotic and the stromal tissues which gave positive reactions with poly-U and ribonucleic acid. These results confirm that different nucleases can be demonstrated histochemically by the use of films of polyribonucleotides, and suggest that tumors may derive from areas of preneoplastic tissue deficient in several types of nuclease activity.