Long term effects of a single dose of dimethylnitrosamine on the rat liver.

A single injection of DMNA induces in hepatocytes different lesions which are revealed by the mitoses following a partial hepatectomy. The inhibition of mitotic activity, the appearance of micronuclei and the development of hyperplastic nodules were investigated. The results show that the delay between the DMNA treatment and the induction of mitotic activity influences differently the evolution of these changes. The lesions reponsible for the inhibition of mitotic activity and the production of micronuclei are produced when DMNA is given before hepatectomy. They remain unchanged for a long period and are still present five weeks after the injection of the carcinogen. They have disappeared after 10 weeks. On the contrary, the lesions leading to the formation of hyperplastic nodules are at their greatest when DMNA is given at the time of the DNA synthesis following hepatectomy. The data of the present work are compared with previous results obtained by combining X irradiation and hepatectomy.