The immediate and prolonged effects of p-dimethylaminoazobenzene on the increase in weight, net amount of pentose- and deoxypentosenucleic acids and acid deoxyribonuclease activity in the rat liver after partial hepatectomy have been studied.

A slight depression of the rate of dry weight increase was noted after feeding DAB to the rats for 60 days. Discontinuation of the carcinogen brought about normal conditions. No immediate or prolonged effects of DAB on the rate of PNA formation were recorded. A considerable reduction of the rate of DNA formation was found after only 25 days' administration of DAB. The same reduction was found at 60 days, but a return to normal conditions was noted after discontinuation of the carcinogen. An initial stimulation of the postoperative DNase increase was demonstrated. This stimulation after 25 days' administration of DAB was followed by a depression at 60 days. The DAB-induced reduction of the capacity of the liver cells to respond to a growth stimulus with an increase in the average cellular DNase activity was sustained even after discontinuation of the carcinogen.

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Some of these investigations were carried out during the tenure of a Visiting Research Fellowship at the Laboratories of the Division of Nucleoprotein Chemistry, Sloan-Kettering Institute for Cancer Research, Sloan-Kettering Division of Cornell University Medical College, New York, N.Y.

This investigation was supported in part by funds from the National Cancer Institute, National Institutes of Health, Public Health Service (Grant CY-3190), and by grants from the American and Swedish Cancer Societies.

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