DNA adduct formation in rat, human and hamster pancreas treated with methylnitrosourea

The methylation of cellular macromolecules with dimethylnitrosamine (DMN) and methylnitrosourea (MNU) was studied in organ cultured rat, hamster and human pancreatic explants. At concentrations of DMN and MNU that caused similar methylation of protein in human explants DMN caused only 2.6% and 0.3% of the methylation of DNA and RNA that was produced by MNU. The DNA of explants treated with MNU was analyzed. The O6-methylguanine (O6-MeG)/7-methylguanine (7-MeG) ratio was greater in the hamster DNA than in DNA isolated from either rat or human. The time course of removal of methyl adducts from DNA was followed for 6 h after treatment with MNU. No decline in O6-MeG occurred during this period in hamster explants, although there was a decline in the content of 7-MeA and 3-MeA, whereas there was removal of O6-MeG in the DNA from human pancreas explants.