Effect of aging and gamma radiation on acetylation of rat liver histones.

We studied age-related and radiation induced changes in histone acetyltransferase activity and acetylation of histone fractions in normal and regenerating rat livers. Male Wistar rats aged 1-28 months were used through the studies. They were exposed to whole-body doses of 5.7 Gy gamma radiation from a 60Co source and partial hepatectomy was carried out 30 min after irradiation. Within nuclei isolated from normal and regenerating livers of rats, acetyltransferase activity of histones increased with age. An age-dependent decrease in histone acetyltransferase activity in normal and regenerating rat livers was also obvious at the time of maximum activity (i.e. at the 4th min of incubation). The radiation-induced drop in acetyltransferase activity was mild in normal livers. Twenty-four hours after partial hepatectomy, acetyltransferase activity in regenerating livers was almost completely inhibited by irradiation. The acetylation of histone fractions and subfractions was not equal. The highest activity among all histone fractions was found in fraction H4. In regenerating livers of non-irradiated and irradiated rats, there was a greater rate of acetylation in tetraacetylated subfractions of histone H4 compared with intact livers.