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Litters of 8- to 10-day-old nestling rats were protected against whole-body x-irradiation by cysteamine, AET, and deep hypothermia, singly, and by a combination of cysteamine pretreatment and deep hypothermia. The different treatments were randomized among littermates to minimize animal variation. A comparison of the LD50(30) values obtained for the different treatments gave a dose-reduction factor of 3.3 for the combined treatment, which was significantly greater than the factor for hypothermia alone, 2.6, or that for cysteamine alone, 1.4. Cysteamine therefore provided additional protection in the fully hypoxic (hypothermic) animal. Judged from the histological appearance of the gonads of the surviving male nestling rats, killed 30 days after irradiation, hypothermia afforded some protection to the germinal epithelium. Cysteamine, although injected when the testes were abdominal, had no demonstrable protective effect.

A chemical mixture containing 25 Amoles of MEA, 7 pmoles of AET, and 2 micromoles of 5-HT was found to be of significant value in protecting mice against repeated exposures of 800 R, 1100 R, or 1400 R given at intervals of 28 days. Dose-reduction factors of 2.17, 2.18, 1.95, 2.14, and 1.58 were obtained for the first five exposures. Following the first exposure there was no chemical mortality. The beneficial value of this mixture, however, was limited by the incidence of chemical toxicity which was more prevalent in mice with higher cumulative doses of radiation.