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

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Abstract
Films of polycytidylic acid (poly-C) and polyuridylic 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 RNA. 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 RNase activity. In livers of 4-dimethylaminoazobenzene fed rats, the centrilobular necrotic tissue was negative to poly-C and strongly positive to poly-U and RNA. The regenerating parenchyma gave positive reactions with the different substrates but areas of the hyperplastic tissue became deficient in all 3 hydrolase activities after 8 wk of azo dye feeding. The hyperbasophilic foci that developed a few weeks later were inactive against poly-C, poly-U and RNA, and so were the hepatomas except for necrotic and stromal tissues which gave positive reactions with poly-U and RNA. 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.