THE EFFECTS OF HYPOPHYSECTOMY AND OF THYROXINE ON THE RADIATION-INDUCED CHANGES IN THE RAT THYROID1

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Abstract
CELLULAR hypertrophy and nuclear changes are impressive histologic features of the thyroid of the rat previously irradiated by the administration of I131 (Maloof, et al., 1952). These findings have been observed as early as one month and have persisted for as long as 18 months after a total radiation dose of only 5800 roentgen equivalents physical (5 μc, of I131) in spite of an abundant supply of iodine (3 μg./gm. food) in the diet. Not all the cells are equally affected; the abnormal nuclei are scattered, but the cellular hypertrophy is constant and intense. These changes vary, depending upon the initial dose of I131. It has not been clear whether the cellular hypertrophy and nuclear changes are direct results of the ionizing radiation upon the cells themselves, or whether the cells are conditioned by the radiation, the subsequent changes arising secondarily from increased thyrotropic hormone stimulation resulting from a reduced rate of hormone synthesis by the irradiated thyroid gland.