DNA repair synthesis in guinea pig pancreatic slices following in vitro exposure to N-nitrosomethylurethane.

The incorporation of thymidine into DNA in the presence of hydroxyurea (HU) by guinea pig pancreatic slices following exposure to N-nitrosomethylurethane (NMUT) was used to follow DNA repair synthesis. HU was used to suppress normal replicative DNA synthesis. Slices from the duodenal segment of the pancreas were exposed for periods of 15 to 90 min to NMUT at concentrations of 2 to 20 mM, then incubated in tritiated thymidine ([H3]-TdR) free of carcinogen, and radioactivity in DNA was determined. NMUT induced a a dose- and time-dependent increase in HU-insensitive thymidine incorporation. This stimulated incorporation, which could be attributed to repair synthesis, occurred immediately following the treatment and was largely complete within 3 h.