The Effect of a Single Systemic X-Irradiation of the C57BL Mouse on the Nucleodepolymerases of the Thymus

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Abstract
Thymic nucleodepolymerases were studied in C57BL mice after single, whole-body X-irradiation. The depolymer-ases were: deoxyribonuclease (DNase), heat labile ribonuclease (RNase 6), and heat stable ribonuclease (RNase 8). Activities were measured by release of UV absorbing acid-alchol soluble material from nucleic acids by thymic homogenates. Mice were sacrificed at intervals from 20 minutes to 7 days after 160 r 120 KVP X-ray. The average amount of enzyme per cell increased for all activities within 24 hours after X-ray, and was 6 and 10 times normal for DNase and RNase 8, respectively, at that time. RNase 8 in terms of organ content also increased up to 24 hours post X-ray. The 24 hour X-ray data were compared with data obtained 24 hours after injection of sufficient hydrocortisone to give a similar thymic weight loss. With the latter treatment, DNase and RNase 8 were only three times normal. All depolymerases were above normal, in terms of cell content 24 hours after 40 to 160 r. The increases in DNase and RNase 8 were approximately linear with dose, RNase 8 rising more rapidly. The increase in RNase 6 was the same at 40, 80, and 160 r. It was concluded that the differential effect of X-ray on thymic cell classes could not account for the increases observed.

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