[Diurnal rhythm of cell proliferation at the late stages of precancerous changes in the liver induced by ortho-aminoazo-toluene].

Orthoaminoazotoluol was administered to mice for a period of nine months. Circadian rhythms of mitotic activity and the number of the DNA-synthesizing cells were determined by autoradiography (with the use of 3H-thymidine) at the second (adenomatous nodes) and the third (primary hepatoma) stages of carcinogenesis in the developing tumours and the surrounding liver parenchyma. The listed structures proved to have a single-peak rhythm of mitotic activity with the maximum of mitoses at 4-7 a. m.; the labeled nuclei circadian rhythm was double-peaked with the maximum at 7 p. m. and 4 a. m. The mean 24-hour values of both indices at the second and third stages of hepatocarcinogenesis were much greater than in the surrounding non-tumour tissue of the liver.