Potent mitogenic activity of 4-acetylaminofluorene to the rat liver.

Administration of 4-acetylaminofluorene (4AAF) to rats by oral gavage (1000 mg/kg) produces a wave of S-phase activity in the liver 36 h later, followed by a wave of mitoses at 48 h. These events were monitored by autoradiography of isolated hepatocytes and by histopathology, respectively. DNA-labelling was shown to occur following both in vivo and in vitro radiolabelling. The level of S-phases observed approached that reported following partial hepatectomy. These effects were not accompanied by unscheduled DNA synthesis (UDS) nor was any frank histopathological damage to the liver evident. 2-Acetylaminofluorene (2AAF) elicited a very weak S-phase response at a dose level of 50 mg/kg, but gave marked UDS between 12 and 48 h.