Pulmonary and lymph node lesions and leukopenia which developed in dogs after plutonium-239 and -238 dioxide inhalation have been related to various radiation dose parameters, over a wide range of postexposure time intervals (16-468 days). The degree of radiation pathology in lungs was found to increase with increasing accumulated alpha doses above 1500-2000 rads and up to about 15,000 rads. In general no damage to tracheobronchial lymph nodes was evident unless radiation changes were also present in the lungs. The degree and extent of the lymph node changes did not correlate well with estimates of total lymph node dose, but there was a relatively good relationship with dose rate (rads per day) to the lymph nodes adjacent to trachea and main bronchi. Radiation changes in both types of tissue, and due to both plutonium isotopes, were unrelated to length of postexposure period except for increasing fibrosis with time. In contrast, the leukopenia which developed was related to mean, post-exposure, fixed tissue burdens but not to rad dose except in experiments of similar duration. The findings indicate that the lung lesions reflect total accumulated pulmonary doses while lymph nodes are more sensitive to dose rate. It is suggested that the leukopenia developed as a result of irradiation of circulating cells by localized deposits of plutonium in lymph nodes and probably lungs, rather than to depression of hematopoiesis and/or lymphopoiesis.

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