[Circadian rhythms of cell proliferation in mice during the early stages of hepatocarcinogenesis induced by ortho-aminoazotoluol].

The 24-hour rhythms of the mitotic activity and the changes in the number of DNA-synthesising cells were studied in mouse hepatocytes at the early stages of carcinogenesis of the liver induced with orthoaminoazotoluol in these animals; the autoradiographic method with thymidin-3H was used. During the first stage (that of diffuse irregular hyperplasia) and the second stage (that of focal proliferation) the rhythms of of the changes in the mitotic activity of test animals as incontrols had a distinct monophasic character with the maximum number of mitoses at the early morning hours and the minimum at the evening-night hours. Under normal conditions and during the first stage of carcinogenesis of the liver the DNA-synthesizing cell rhythms had a distinct monophasic character with the maximum during the day and evening hours, respectively; during the second stage of carcinogenesis the rhythm was characterized by the appearance of the second maximum at the early morning hours. The mean 24-hour values of both indices increased during the carcinogenesis.