Effect of Whole-Body Irradiation on the Activity of Acid Deoxyribonuclease of Mouse Tissues

Abstract

The effects of whole-body irradiation on the activity of acid deoxyribonuclease (DNase II) in lymphoid tissues have been studied by numerous workers during the last ten years. The specific activity of deoxyribonuclease II in rat spleen and in thymus (1, 2) was found to increase 12 to 24 hours after irradiation. The level of the enzyme remained constant, however, when expressed as total activity per organ. Increase in organ activity was detected in lethally irradiated mice (3, 4). A release of deoxyribonuclease II into urine and plasma was also reported to occur in rats after irradiation (5, 6). It has been suggested that the primary cause of death of cells postirradiation is a release of hydrolytic enzymes into the cytoplasm from damaged lysosomes (7); release of bound deoxyribonuclease II has been considered to precede the increase of the specific activity found in rat spleen homogenates (8-10). In this investigation the changes of activity of acid deoxyribonuclease were studied in tissues of Ha/ICR Swiss mice after exposure to sublethal doses of wholebody irradiation. An increase of the total organ activity of deoxyribonuclease II was found in both thymus and spleen (11). A release of deoxyribonuclease II into the soluble fraction of spleen homogenate was observed only at the highest dose of radiation used. Stimulation of the pituitary adrenal axis did not account entirely for the radiation-induced increase of deoxyribonuclease II activity. The changes of enzymatic activity seen were not unique for radiation, since they were observed also when involution of lymphoid tissues was caused by agents other than radiation. The destruction of lymphoid tissues appeared to be directly related to the increase of activity of this enzyme.