Urinary excretion of 06-butylguanine after the administration of N-nitroso-N-butylurea in rats

0⁶-Butylguanine was detected in the urine of rats given the butylating agent N-nitroso-N-butylurea. O⁶-Butylguanine contents in the 24-h rat urine samples after i.p. doses of 50, 100, and 200 mg/kg N-nitroso-N-butylurea were 1.03 ± 0.41 (SE), 8.30 ± 1.70, and 59.53 ± 6.52 pmol, respectively. This suggests that O⁶-butylguanine formation in nucleic acids might be repaired in vivo, possibly by base excision, besides other mechanisms. After i.v. doses of 0.1 and 1 mg/kg of O⁶-butylguanine to rats urinary excretion did not exceed 2% of the administered dose, suggesting that the amount of O⁶-butylguanine effectively released by base excision might be much larger than that detected in the urine after N-nitroso-N-butylurea. Inhibition of the enzyme O⁶-alkyl-DNA transferase by N-nitrosodimethylamine increased urinary O⁶-butylguanine resulting from exposure to N-nitroso-N-butylurea (100 mg/kg i.p.) up to four times, thus confirming an alternative DNA repair mechanism.