Effect of cadmium and ionizing radiation on histones in rat brain

Changes in constituent part of the chromatin, histones, were studied in brain of rats 1-21 days after administration of cadmium (3 mg CdCl 2 /kg i. p.) and/or whole body irradiation (3 Gy of γ-rays). In the brain hemispheres, increase in content of histones and histone/DNA ratio was found at some intervals after administration of cadmium alone or in combination with irradiation. In course of the first 2 weeks, relative proportion of individual histone fractions altered especially after combined treatment. At later intervals, in irradiated rats, relative proportion of H1 0 subfraction increased in H1 fraction. In the cerebellum, the changes of histones were more profound than in the brain hemispheres. Due to decrease in histone content, the histone/ DNA ratio decreased in the cerebellum of rats of all experimental groups. The most marked decrease in histone/DNA ratio occurred after combined treatment (Cd+lr). The changes in relative proportion of individual histone fractions were detectable from the 7th day in all groups of experimental rats, most conspicuously in the group Cd+lr. The proportion of H1 0 subtraction in the H 1 histone fraction increased mainly on the 7th day after treatments. In general, character of histone alterations induced by administration of cadmium was similar to that induced by γ-irradiation. In majority of cases, after combined treatment (cadmium administered 30 min before irradiation), the alterations of histones were more profound than after single treatment. This finding suggested that partial summation of the 2 factor effects occurred after the combined treatment.