Radiosensitivity of Various Tissues of the Rat with Special Regard to Deoxycytidine -2-$^{14}C$ Metabolism in Vitro

The effect of 400 R of whole-body X-irradiation on DNA synthesis, DNA degradation, CdR-aminohydrolase activity and oxygen uptake in the liver, spleen and thymus of the rat has been studied in connection with the radiosensitivity of these tissues. The rate of CdR-2-$^14 C$ incorporation has been followed during the postirradiation period and has been correlated with the increased levels of CdR-aminohydrolase activity druing this period. The postirradiation period comprises radiation reaction and tissue regeneration periods. During the period of radiation reaction, markedly decreased precursor incorporation, decreased tissue levels of DNA and decreased uptake of oxygen are noted as well as an increase in the CdR-aminohydrolase activity. The period of regeneration appears to consist in two discrete phases. The first phase reveals a return of CdR-aminohydrolase activity and the second phase is highlighted by a markedly increased rate of labeled CdR incorporation. Various events occurring during the radiation reaction period and the regeneration period in the three tissues studied can be considered qualitatively the same, differing only in the degree of acute cell death, in the duration of the delay of DNA synthesis in the sruviving cells, and in the rate of recovery resulting from accelerated cell replication during the period of regeneration. A possible biochemical mechanism involved in the DNA synthesis and degradation, in connection with the inreased levels of CdR-aminohydrolase after irradiation, has been briefly discussed.

흰쥐에 400R의 X 線을 一時全身照射하여 肝, 胸腺組織에 있어서의 DNA合成, DNA分解, CdR-aminohydrolase의 活性 및 酸素消費量에 미치는 放射線의 影響을 이들 組織의 放射線感受性과 關蓮시켜 比較檢討하였고 特히 放射線에 의한 CdR-2-$^14 C$의 吸收率의 減少와 CdR-aminohydrolase 活性의 增加와의 關係에 대하여 考察하였다. 放射線에 의한 組織의 變化는 放射線의 作用基와 組織의 再生基에 따라서 判異하게 나타난다. 作用基에 있어서는 DNA 前驅物質의 吸收率, 組織內 DNA의 含量 및 酸素消費量은 顯著한 減少를 나타내나 CdR-aminohydrolase의 活性은 오히려 增加한다. 再生基에 있어서는 먼저 CdR-aminohydrolase의 活性의 回復이 앞서 일어나고, 뒤이어 CdR-2-$^14 C$의 吸收率과 DNA含量에 回復이 일어나며 다시 그 뒤를 이어 酸素消費量에 回復이 일어난다. 이러한 여러 가지 變化는 定性的인 面에서는 세 組織에서 거의 같은 樣相을 나타내는 것으로 추정되나, 定量的인 面에서는 組織의 放射線感受性의 差異, 즉 細胞의 死滅, 生殘細胞內에 있어서의 DNA의 合成이 遲延되는 其間의 長短 및 再生率등에 따라서 다르다. 아울러 放射線照射에 의한 DNA의 合成 및 分解에 따르는 生物學的인 機作을 CdR-aminohydrolase의 活性增加의 觀點에서 考察하였다.