Rate constants for the hydrogen abstraction reactions of hydroxyl radicals from aliphatic amino acids were determined by the p-nitrosodimethylaniline method in gamma-irradiated aqueous solutions. Partial reactivities for the hydrogen abstraction reactions were estimated for C-H bonds found in molecules of aliphatic amino acids, on the basis of the rate constants of glycine, alanine, valine, and leucine and also by assumption of the linear relationship between the position of carbon atom and natural logarithm of the difference in activation energy. The calculated rate constants from the estimated partial reactivities were found to be in good agreement with the observed ones.

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The uptake and release of radionuclides, ¹³⁷Cs, ⁶⁵Zn, ⁶⁰Co and ⁴⁵Ca, by fresh water phytoplankton Anabaena variabilis, which is one of the bluegreen algae, were followed through all growth phases of algae. The amount of adsorption of radioactivity on cellular surface of algae fixed with formarin solution was smaller than that radioactivity taken up by living algae. The radionuclides, except for ⁴⁵Ca whose stable element was one of the elementary nutrients, were noticeably concentrated on the early phase, especially on the exponential growth phase. Thereafter, the activity concentration in algae were decreased by biological dilution due to cell division and reached the equilibrium. The degree of the decrease of radioactivity in algae due to biological dilution was in the order, ⁶⁰Co, ⁶⁵Zn, ¹³⁷Cs. In the case of ⁴⁵Ca, the phenomenon of biological dilution was not observed on every growth phase. The uptake and release of radioactivity by algae occured in the dark, but the amount of radioactivity taken up was smaller than in the light.

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Fifty-six-day-old male ddk mice at the starting of the investigation were used as subjects through the experiment for 64 weeks. After 15 days' preliminary training, and 16 times of weekly trial training using complete maze, 15 mice received a single 224 rads of X-rays (S group), another 15 mice received two 112 rads spaced two weeks apart (F group) and another 15 mice were sham-irradiated (control group). Then those mice were tested on the multiple T-maze with nine-choice points and change of performance was observed in terms of errorchoices by giving one test trial a week. We introduced the concept of "confusional trials" as an index for surmising to what extent mice failed to exhibit good maze learning habits. In the results, the F group showed significantly worse performance than the two other groups at early stages, opposite to it the S group exhibited the same, but at late stages after irradiation. The worse performance of F group should be considered to be due to the psychological after-effect to fractionated irradiation and that for S group could be assumed to be due to the acceleration of aging by the irradiation.

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Hyperthermia and radiation interact synergistically in cultured mammalian cells. Data pertaining to the subject are reviewed and mechanisms to explain the phenomena are proposed. One may involve changes in chromosomal structure at high temperatures. These changes make the chromosome less amenable for repair of radiation damage. A second mechanism consists of endonucleolytic degradation of DNA in hyperthermic cells after radiation. This may be ascribed to imbalance between degradation and resynthesis processes operating during repair of DNA damage.

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The process of ovarian tumorigenesis in ddY/F and C3H/Tw mice was studied at various times until 18 months after whole body irradiation with a single dose of 130 R or 260 R of X-rays. The first ovarian tumors were observed at 9 months after irradiation in ddY/F mice. In a total of 28 of 71 ddY/F mice, 33 ovarian tumors were developed, which were subdivided to 25 luteomas, 4 granulosa-cell tumors, one mixed cell tumor and 3 tubular adenomas. On the other hand, 21 of 29 C3H/Tw mice had altogether 32 tubular adenomas and one mixed cell tumor. At older ages, small interstitial cells with eosinophilic cytoplasm were observed in irradiated ovaries. The cells resembled luteoma cells. Luteoma may be derived from the small interstitial cells.

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Rate constants for the hydrogen abstraction reactions of hydroxyl radicals from aliphatic peptides and N-acetyl amino acids were determined by the p-nitrosodimethylaniline method in gamma-irradiated solutions. For peptides, enhancement of reactivity toward hydroxyl radicals was expected, because of disappearance of suppression by NH₃⁺ group. The expectation was confirmed by the obtained rate constants. In order to estimate the partial rate constants for peptides, partial rate constants for the hydrogen abstraction reactions from amino acids were corrected by the factors calculated on the basis of effect of peptide bond formation. The rate constants of peptides and N-acetyl amino acids calculated from the corrected partial rate constants were in good agreement with the experimentally obtained ones.

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A single intraperitoneal injection of partially purified ginseng extract after X-irradiation of 650-675R significantly increased the 30-day survival ratio in mice.

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