Aging and radiation induced alterations in liver histones.

Age-related changes in histones in the liver of normal rats and in rats irradiated with 5.7 Gy gamma rays were examined. Quantitative histone changes in growing and aging rats (from 1 to 28 months of age) were found to be mild only. As they paralleled the DNA changes, the histone/DNA ratio remained stable with age. In total extracted histones there was a decrease in the H1 proportion in older age groups with preceding increase in the H10 proportion. Thirty minutes after irradiation the amount of histones was reduced with age, probably due to an impaired extractability of histones. As the quantitative DNA changes were milder, the histone/DNA ratio decreased in aging liver after irradiation. Similar patterns of changes in proportion of the H1 fraction and H10 subfraction were observed in irradiated and nonirradiated animals, in the former with an earlier onset. Irradiation, therefore, accelerated spontaneous age-related alterations.