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Focal Loss of Ribonuclease Activity in Preneoplastic Rat Liver¹

Laboratories de Recherche, Institut du Cancer de Montréal, Hôpital Notre-Dame, and Département d'Anatomie, Université de Montréal, Montréal, Canada

The distribution of RNase activity in livers of rats fed 4-dimethylaminoazobenzene and of rats fed 3'-methyl-4-dimethylaminoazobenzene has been examined by means of an improved substrate film method. The development of liver nodules in these animals was found to be accompanied by a loss of RNase activity. This loss was focal, and it preceded the formation of hyperbasophilic foci and hepatomas, which were also RNase negative. The study further revealed that the loss of RNase activity occurs earlier in animals fed the highly potent 3'-methyl derivative than in those submitted to the less active azo dye. The results suggest that a deficiency in RNase activity may represent a prerequisite in tumor formation.

¹ This investigation was supported by grants from the National Cancer Institute of Canada and also by grants from La Fondation J. H. Biermans and Les Fondations J. Rhéaume. A preliminary report of this work was presented at the 62nd Annual Meeting of the American Association for Cancer Research held in Chicago, Ill., April 8 to 10, 1971 (3).

² Research Associate of the National Cancer Institute of Canada.

Received 5/30/72. Accepted 8/14/72.