Variations in the Cell Cycle During Azo Dye Hepatocarcinogenesis<xref ref-type="fn" rid="FN2">2</xref>

Abstract

Radioautographic and cytophotometric studies were undertaken to determine whether variations in the duration of the G2 phase of the cell cycle occur in rat hepatocytes during 4-dimethylaminoazobenzene (DAB) carcinogenesis. In hepatic nodules of DAB-fed rats, a decrease in the number of labeled mitoses was accompanied by an increase in the level of ploidy, indicating a delay or an arrest of cells in the G2 phase of the cell cycle. In hyperbasophilic foci considered as the sites of neoplastic transformation, higher percentages of labeled mitoses were obtained and ploidy was reduced, indicating a shortening of the G2 phase. Thus it seems that neoplastic transformation is associated with an elimination or inhibition of both the G1 and G2 blocks of the cell cycle. Both changes contribute to the acceleration of cell proliferation in sites of tumor formation.