Effect of age on the induction of 8-oxo-2'-deoxyguanosine-releasing enzyme in rat liver by gamma-ray irradiation.

Aged (27 months of age) and young (6 months of age) Fischer 344/DuCrj rats were exposed to gamma-ray irradiation, and their livers were compared for levels of oxidative DNA modifications and repair enzyme activities. The amounts of 8-oxo-2'-deoxyguanosine (8-oxodG) in the nuclear DNA of the livers of both young and aged rats increased immediately after irradiation, by 1.7-fold in the livers of young rats and 2.7-fold in the livers of the aged rats. Also, the rate of 8-oxodG decay was slower in the livers of the aged rats than in young rat liver, and remained above the baseline level even 1 week after irradiation. The activities of 8-oxodG-releasing enzymes peaked 2 and 6 h after irradiation in the livers of young and aged rats, respectively. The repair activity in the livers of the young rats was increased by sevenfold 2 h after irradiation, while the livers of the aged rats showed a twofold increase 6 h after irradiation. These results suggest that the ability to repair damaged DNA is lower in aged rats, and that the accumulation of oxidative DNA damage that takes place during aging may be related to this decline in repair activity.