Age and Its Influence on Effects of Iodine-131 in Guinea Pig Thyroid Glands

Abstract

To identify the differences in age-related radiosensitivity of the thyroid gland to radioiodine exposure, we exposed fetal, neonatal, weanling, and adult guinea pigs to single graded doses of 1311I. Injected quantities ranged from 1 to 100 CCi 13'I, depending on the age group, and resulted in thyroid doses ranging from hundreds to tens of thousands of rad. At approximately 100 days of age (or 100 days after dosing for adults), a single microcurie of 31I was given and animals were killed 1 day later to provide data on thyroid weight and percentage 1311 uptake. Analysis of these data and information on pathology suggested that the fetal and weanling guinea pig thyroid glands were more radiosensitive than the adult thyroid; the neonatal thyroid appeared less radiosensitive than that of the adult. The increase in radiosensitivity of the young thyroid glands over the adults, however, did not appear to be greater than twofold. Nevertheless, the demonstration of age-related radiosensitivity requires that it be considered by those who assess radiologic risks to human populations.