Effect of X irradiation on histones and DNA in rat thymus

Changes in histones and DNA in rat thymus during 14 days after irradiation with various doses (0.96 Gy, 2.87 Gy, 5.74 Gy and 9.57 Gy) of X-rays were studied. After the temporal increase at hour 3 after irradiation histone concentration in thymus nuclei was decreasing in dose dependence with minimal values on day 3. After this period, in animals irradiated with lower doses histone concentration increased to 85% of control values already on day 5, while at dose 5.74 Gy it did not exceed 42% of the controls neither on day 14. Animals irradiated with 9.57 Gy died between days 3 and 5 after irradiation. DNA concentration in thymus nuclei decreased significantly at hour 24 after irradiation. The course of changes in this parameter was similar to that of histone concentration changes in the following period. Recovery of DNA concentration was, however, protracted till day 14 and it was completed in this time after irradiation with lower doses. Irradiation caused changes also in individual histone fractions. It is supposed that the increase in arginine-rich fractions plays a certain part in initiation of repair. (author)