Study on late effects of radioiodine on rats.

This paper describes the results observed on 850 male Wistar rats for two years after intraperitoneal injection with 131I, 132I or 125I of different radioactivities. The incidence of thyroid malignant tumor was 45.8% when the dose absorbed by the thyroid gland was 7.8 Gy in the 131I groups, and even tumors of lung and soft tissue, and malfunction of kidney and immune organs could be elicited when the radioiodine was overdosed. Both 132I and 125I have their optimal carcinogenic dose ranges and optimal doses of carcinogenesis. As the dosage decreases to a certain level, a low-limit dose incapable of inducing cancers may be present. 131I induced mainly papillary and mixed type carcinomas, 132I chiefly follicular and undifferentiated type carcinomas, while 125I induced follicular and medullary carcinomas. The paper also discusses cytochemical DNA quantitative assays of different histological types of thyroid gland carcinomas, holding that reference to such data as decreasing serum T4, elevating serum TSH and CIC may be helpful for early diagnosis of thyroid carcinomas.