FUNCTIONAL AND STRUCTURAL CHANGES CONSEQUENT TO HIGH DOSAGES OF RADIOACTIVE IODINE*†

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Abstract
Admn. of doses of radioiodine that will produce an intrathyroidal concn. of at least 4 [mu]c/mg. of tissue results in complete thyroidal destruction. The rate and histopathologic pattern of cellular death varies with the size of the dose. Intrathyroidal concns. of 2 [mu]c/mg. produce partial glandular destruction. Thyroid tissue surviving such dosages is morphologically atypical, fails to regenerate. It appears to be functionally atypical in a reduced ability to take up tracer I131, and in its inability to prevent "thyroidectomy" changes in the pituitary. Intrathyroidal doses of 1 [mu]c/mg. or less produce no permanent changes. Other effects of high dosages of I131 in mice include (1) Curtailment of growth, (2) temporary reduction in oxygen consumption, (3) parathyroid injury, (4) tracheal mucosal lesions and tumors, (5) recurrent nerve injury, (6) ovarian sterilization, (7) fatal chromophobic tumors of the anterior pituitary.