Late effects of roentgen irradiation. I. Studies on rats irradiated under anoxic anoxia.

Abstract

In the fall of 1949, studies were carried out on the effect of anoxia on roentgen irradiation injury in rats. At that time it was demonstrated that irradiation under extreme anoxia shifted the LD 50 measured at 30 days from a little over 600 r to over 1,200 r (1). All of the animals from groups irradiated at 1,000 r, 1,200 r, and 1,400 r which survived 30 days were kept for further observation. Because of limited caging space, only a small sampling of the groups irradiated at 600 r and 800 r were kept. As determined by body weight and clinical observation, all of the animals appeared to have recovered at the 30-day period of observation, when such experiments are usually terminated. These animals have now been observed for 540 days. Methods and Results All of the rats used in this study were from the Wistar strain. The details of the irradiation technics used and the post-irradiation course for the first 30 days are given in an earlier report (1). The procedures used in the present studies were as simple as possible. The rats were kept four to a cage, fed Rockland rat chow, weighed weekly, and observed for any changes. Animals showing marked weight loss or other evidence of disease were sacrificed as they became terminal, and tissues were taken for histologic examination. Eight unirradiated rats were kept as controls under identical conditions. The first significant finding was a marked shortening of the life span (Fig. 1). This occurred in spite of the protection furnished by the anoxia against the lethal action of x-rays in the immediate post-irradiation period. Exactly how much the life span was shortened could not be determined, since our colony was new, and we had no data on longevity of normal rats except for the small group of controls included in this experiment. From values found in the literature, the shortening of life span was at least 50 per cent, even in the animals receiving only 800 r (7, 29). Weight curves of four typical animals are shown in Figure 2. Our clinical and postmortem observations indicate that there were three post-irradiation periods. Period one was from the 30th to approximately the 100th day; the second period was from the 100th to approximately 300 days; and the third period from 300 days to 540 days. Period I: 30 to 100 days: Respiratory infections developed first in the 1,400 r animals, and then in the 1,200 r animals, progressing into pneumonia. The onset of infection was associated with a rapid and marked weight loss, and death resulted usually within a couple of weeks. Autopsy findings of interest on these animals were chiefly confined to the lungs, where varying degrees of lobar and bronchopneumonia were found. A purulent empyema and pericarditis frequently accompanied the pneumonia. The bone marrow and other tissues were examined and were found to be normal.