Tritiated water was given to rats of various ages through a stomach tube. For the excretion study urine sample was collected periodically and its tritium concentration was determined with a liquid scintillation counter. The result showed clearly that the tritium metabolism depends on the age of the animal. The general trend was that the older the animal the longer the biological half life of tritium. The exception of this was the slightly longer biological half life for sucklings than that of weanlings. For tissue distribution study, experimental animals were sacrificed periodically after administration of tritiated water. Tritium incorporation was assessed both in the aqueous fraction and in the organic component of tissues from various organs, including the blood, brain, liver, muscle and testis. During the first several days after administration the tritium concentration in the tissue water decreased rapidly while that in the tissue organic matter decreased more slowly. This was more notable in the younger animals. In the weanlings, the tritium concetration became lower in the tissue water than in the tissue organic matter about 12 days of postadministration in contrast to the 24 days in the adult rat.

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Human placental extracts worked as a strong antimutagen on ultraviolet light (UV)- and gamma-ray-induced mutations in Escherichia coli WP2 B/r trp.

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The ratio of organ dose to surface dose in a rat exposed to conventional therapeutic X-rays was measured by TLD implantation method. Pieces of TLD-100 (LiF) in ribbon (The Harshaw Chemical Company) were implanted surgically into the organs of a rat carcass such as the liver, spleen, testis and femur. After the whole body irradiation with therapeutic X-rays, the ratio of thermoluminescence intensities was determined between the implanted TLD and the one fixed on the rat surface facing the X-ray source. The problems affecting the accuracy in the results were examined, which were the contamination of TLD surface with body fluid, the direction dependence of thermoluminescence response and the variation in the effective energy within a rat body. It was found that the dose attenuation due to absorption by the rat tissue itself should not be neglected in the energy range lower than about 80 keV in effective energy.

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A culture system was designed in which proliferation of the haemopoietic stem cells was supported by adherent ‘stromal’ cell colonies. Application of the culture system to studies on kinetic behaviour of the haemopoietic stem cells after irradiation revealed ; i) bone marrow stromal cells were radiosensitive with D_o=95 R, when measured as the capability to proliferate and form adherent cell colonies in vitro, ii) radiosensitivity of the pluripotent stem cells (CFUs) in vitro was within the range of the in vivo sensitivity, iii) irradiated bone marrow cells under in vitro condition could repopulate at the same rate as those under in vivo condition, thereby suggesting that the function related to the support of haemopoiesis was radioresistant, iv) concentrations of both CFUs and granulocyte-macrophage precursor cells (CFUc) were higher in the irradiated cultures than those in unirradiated control culture at 3 weeks after irradiation.

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Radiation protection from bone marrow death by a single injection of partially purified ginseng extact after whole-body X-irradiation was confirmed in JCL-ICR mice. The extract was efficacious both by intraperitoneal and intravenous injection. The extract protected mice when it was injected from 2 days before irradiation to 2.5 hr after that. Recovery of splenic weight and splenic DNA was stimulated by the extract, but that of thymic weight was not. Stimulated recovery by the extract was also observed in thrombocyte and erythrocyte counts, while the extract did not markedly affect recovery of leukocyte counts. The extract also increased 30-day survival ratio of splenectomized mice. In splenectomized mice recovery of only thrombocyte counts was stimulated by the extract. Recovery of thrombocyte counts after exposure is assumed one of the most important factors for restoration of bone marrow death.

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Some properties of the radioprotective substances in a ginseng extract that increased the 30-day survival ratio in irradiated mice were studied. Methanol-soluble fraction of the extract did not protect the irradiated animals. Acid or alkali (0.12 N) inactivated the extract at 60°C. But the radioprotective activity was stable after heating the ginseng extract in physiological saline at pH 7 in a boiling-water bath for 15 min. The ginseng extract was separated into two fractions by CM-cellulose column chromatography. One of them (CM-A) was significantly efficacious at 5% level, and the other (CM-B) at 0.1% level with the doses proportional to their yields. CM-B, not containing saponin, was subjected to further purification, UV spectrum and a biuret test suggested the presence of protein in this fraction. The supernatant obtained after heating CM-B solution at pH 7 was separated into three fractions, namely G-I, G-II and G-III, by gel-chromatography with a Sephadex G-75 column. Both G-I (0.44 mg per animal) and G-III (0.84 mg, calculated dose) were significantly efficacious, but G-II (0.47 mg) was not.

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Experiments were designed to elucidate whether or not the irradiated bone marrow cells receive any stimulation for the self-replication and differentiation from normal ‘stromal’ cell colonies in the bone marrow cell culture in vitro.
When irradiated or unirradiated bone marrow cells were overlaid on the normal adherent cell colonies, the proliferation of haemopoietic stem cells was supported, the degree of the stimulation depending on the starting cellular concentration. There was, however, no significant changes in the concentration of either CFUs or CFUc regardless of the dose of irradiation on the bone marrow cells overlaid. This was a great contrast to the dose-dependent decrease of CFUs or CFUc within the culture in which both the stem cells and stromal cells were simultaneously irradiated.
These results suggest that the balance of self-replication and differentiation of the haemopoietic stem cells is affected only when haemopoietic microenvironment is perturbed.

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Survival in response to hyperthermia at 42 and 44°C, both alone and in combination with X-irradiation was examined in vitro in Chinese hamster V-79, HeLa-S3, murine Ehrlich ascites tumor cells (EH) and murine L-fibroblasts. L-cells were markedly thermo and radiosensitive, while the other three cell lines, although not so sensitive did show similar responses. When each cell line was exposed to split dose Hyperthermia in the 42→44°C sequence, survival after the second treatment was increased for V-79 and HeLa-S3 cells, but was not significantly changed for EH and L-cells. In the case of split dose exposure in the 44→42°C sequence, survival after the second treatment was markedly decreased for V-79, EH and HeLa-S3 cells, but only slightly for L-cells. When hyperthermia at 42 or 44°C was followed by X-irradiation immediately, V-79, EH and HeLaS3 cells showed decrements in both D_q and D_o values, while L-cells showed a decrement only in D_q but no significant change in D_o. From these results, it seems that the hyperthermic damage by exposure to 44°C may be different from that by exposure to 42°C.

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γ-Irradiation of bovine pancreatic ribonuclease A in the presence of cytidine 2'' (3'')-phosphate produced an enzymatically active derivative (s) of the enzyme which was similar to that described by Ukita and Waku (T. Ukita and K. Waku (1964) J. Biochem. 55: 420-431). The V_max-values of the enzyme for two synthetic substrates decreased to half by irradiation, while the Km-values were unchanged. Studies on the affinity of the irradiated enzyme for folic acid suggests that not only the main active site (B₁-R₁-p₁) but also the sub-site (B₂) seems remained intact after γ-irradiation under the conditions used.

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