X-Irradiation in Hamsters, and Effects of Streptomycin and Marrow-Spleen Homogenate Treatment

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Abstract
Streptomycin treatment increased the radiation LD50 (28 days) of hamsters to 800 r from a control value of 700 r, and an intracardial injection of marrow-spleen homogenate increased this to approximately 1080 r. The effect of homogenate on survival showed up earlier than the effect of streptomycin. Streptomycin given for only the first 3 days did not improve survival and it was as effective when started on the 3d as on the 1st day after irradiation. With doses between 1400 and 10,000-r, animals survived 4-6 days. Neither streptomycin nor homogenate alone prolonged survival at 1400 r but the 2 treatments combined did. The combined treatments did not consistently increase the survival of animals given 1050-1160 r above that obtained with homogenate alone. Leukocyte counts in severely irradiated hamsters (LDgo) treated with streptomycin began to recover about 7 days, and in those treated with homogenate about 5 days after exposure. In the latter essentially no anemia developed, compared to values of about 7 g/100 ml 12 days after irradiation in animals not given homogenate. A sharp weight loss occurred at this time in the hamsters not treated with homogenate. Bacteria were isolated from the heart blood of a majority of the untreated hamsters that died after exposure to 550-1160 r. The presence of Pseudomonas was associated with the shortest, and negative cultures with the longest survival times. Streptomycin was more effective in reducing the incidence of positive cultures than in reducing mortality. Homogenate treatment increased resistance to experimental infection with Proteus or Paracolon 7 days after irradiation. The intestinal epithelium showed severe damage but little actual denudation the 3d day after exposure to 1000 r. On the 5th day there was extensive regeneration of the intestinal epithelium in these animals but no regeneration was seen in animals exposed to 2000-4000 r. Submucosal hemorrhage was extensive. Most of the animals showed evidence of bacterial invasion on the 5th but not on the 3d day following irradiation. Streptomycin increased survival in hamsters exposed at intervals of 2 weeks to 450 r (twice) but not to 400 r (3 times). Although in the latter case bacteremia and its reduction by streptomycin were the same as in littermates exposed 5-7 times to 300 r the incidence of positive cultures was low and streptomycin was without effect. Leukocyte recovery failed after the 2d exposure to 550 r or the 3d exposure to 400 r, but moderately good levels were maintained through 7 exposures to 300 r. Severe anemia usually preceded weight loss and death.