NUCLEAR CHANGES IN THYROIDAL EPITHELIUM FOLLOWING RADIATION FROM RADIOIODINE*†

Abstract

A quantitative histochemical method was used to measure desoxyribonucleic acid (DNA) in the nuclei of rat thyroid cells after the animals had been subjected to varying doses of radioiodine (I¹³¹). Only nuclei with diploid values for DNA were found in the normal thyroid. The administration of thiouracil to nonradiated rats produced nuclei containing increased amounts of DNA, up to twice the diploid value—the level at which cell division normally occurs. After moderate doses of radiation, bizarre nuclear forms containing unusually large quantities of DNA were found. These forms were also observed after very small doses of radiation followed by administration of thiouracil. Thus, seemingly insignificant doses of radiation, which did not impair physiologic function, produced latent changes which became evident only with an added stimulus for cell division. To complement these observations, it was found that even small amounts of radiation impaired the ability of the gland to hypertrophy when a goitrogen was given. The increase in DNA indicates that the cells were preparing to divide, either under the influence of an endogenous stimulus, or in response to thiouracil. DNA continued to accumulate in abnormal quantities in these nuclei after cell division should have occurred. It is concluded that that radiation in some way alters the genetic mechanisms, perhaps by destroyingchromosomes, so that the abortive cell division results in amounts of DNA which do not fall into recognizable nuclear classes. The clinical significance of these changes in the thyroid is speculative.