Incorporation and persistence of 5-bromodeoxyuridine in newborn rat tissue DNA

One-day-old BDVI rats were given a mixture 5-[3H]bromodeoxyuridine (BrUdR) and [14C]thymidine (each at 20 mg/kg; 12.8 and 3.53 mCi/mmol, respectively) by intraperitoneal injection. DNA was isolated by a phenol procedure from various pooled tissues up to 21 days later and the levels of BrUdR and thymidine incorporation were determined after formic acid hydrolysis and Dowex-50 chromatography. Incorporation increased to a maximum at 12 h then decreased, the decrease of both products occurring in parallel in all tissues examined but differing in kinetics from tissue to tissue. After 12 h, the relative amounts of 3H and 14C showed no consistent or marked decreases and this suggests that BrUdR is not actively removed from DNA by a repair process under these experimental conditions. This was also the case after a much lower dose of these agents (9 micrograms/kg [3H]BrUdR 22.6 Ci/mmol; 1.3 mg/kg [14C]thymidine 53 mCi/mmol) when the 3H/14C ratios in DNA from various tissues were increased relative to the higher dose and showed only slight differences between 15 h and 21 days after administration.