Effect of a Single Treatment with the Alkylating Carcinogens Dimethylnitrosamine and Methyl Methanesulphonate on Liver Regenerating After Partial Hepatectomy. III. Effect on DNA Synthesis in Vivo and on DNA Polymerase Activity Assayed in Vitro

A single treatment with dimethylnitrosamine (DMN) but not with methyl methanesulphonate (MMS) induces liver cell carcinoma if given during the period of restorative hyperplasia following partial hepatectomy, a higher incidence of tumours being induced if the carcinogen is given during the period of DNA synthesis (24 h after the operation) than if given early in the prereplicative stage (at 6 h). To study the effect of treatment with DMN and with MMS on the regenerating liver, DNA replication was measured in vivo in partially hepatectomised animals treated with the methylating agents, and DNA polymerase activity was assayed in vitro.