Diurnal rhythms of cell proliferation in the early stages of liver carcinogenesis induced in mice by orthoaminoazotoluene

Abstract

The diurnal rhythm of mitotic activity and of the number of DNA-synthesizing cells was studied by an autoradiographic method, using thymidine-3H, in mouse hepatocytes in the early stages of carcinogenesis of the liver induced by orthoaminoazotoluene. The rhythms of fluctuation of mitotic activity in the control animals in both the first (irregular diffuse hyperplasia) and the second (focal proliferation) stages of carcinogenesis in the liver had a distinct monophasic character with a maximum of the number of mitoses in the early morning and a minimum in the evening or night. Rhythms of DNA-synthesizing cells under normal conditions and in the first stage of carcinogenesis of the liver were monophasic in character with a maximum in the afternoon and evening, respectively. In the second stage of carcinogenesis the rhythm was characterized by the appearance of a second maximum in the early morning. The mean dirunal values of the two indices increased in the second stage of carcinogenesis.