Dose-Dependent Effects of H 3 TDR as a DNA Label on the Replication of Liver Cells in the Growing Rat

found that the administration of 2 ,uc of H3TDR per gram of body weight changed the nuclear ploidy pattern of the liver cells of 3-week-old rats to that of 2-year-old animals within 2 weeks (18). To explore these observations further, experiments were performed on the replication times and patterns of liver cells in the growing rat, after the administration of several dosage levels of H3TDR. Preliminary results have shown that there is a disruption of the regular rhythmic multiplication of the liver cells (29). In the present report these studies have been extended and include observations on the nuclear ploidy classes engaged in cell replication, as well as on the expansion of the thymidine pool. The results show that the administration of H3TDR may upset the normal, orderly rhythm of liver cell multiplication, may delay the passage of the cells