The Effects of Aflatoxin B₁ and Dimethylsulfoxide on Thymidine-³H Uptake and Mitosis in Rat Liver¹

DNA synthesis, measured by thymidine-³H labeling of nuclei in autoradiographs, and mitosis have been studied in the livers of 148 weanling Fischer rats given a single intragastric dose of aflatoxin B₁ in dimethylsulfoxide and in 190 control rats given either dimethylsulfoxide, isotonic sodium chloride, or no treatment. A marked reduction in both DNA synthesis and mitosis in the parenchymal cells occurred within 7 hr after the administration of aflatoxin and persisted for approximately 50 hr, after which both parameters of cell division returned to normal. DNA synthesis was reduced in the Kupffer cells also, but less severely than in the parenchymal cells. There was histologic evidence of damage to both parenchymal and Kupffer cells within 3 hr after the administration of aflatoxin. Controls given dimethylsulfoxide showed an elevation of hepatic parenchymal mitoses 6 through 50 hr later in 2 out of 4 experiments and no significant change in the other 2 experiments. There was vacuolation of the liver cells but no other histologic abnormality.