THE CYTOLOGICAL CHANGES THAT OCCUR IN THE ANTERIOR PITUITARY GLANDS OF RATS INJECTED WITH VARIOUS DOSES OF I131AND THEIR SIGNIFICANCE IN THE ESTIMATION OF THYROID FUNCTION1

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Abstract
A cytological study of the pituitaries of rats injected with 18, 300, 525, and 875 microcuries of I131 is presented. The findings have been used in evaluating the extent of thyroid function in the animals. The injn. of 18 microcuries of I131 resulted in no cytological changes in the anterior pituitary. From several lines of evidence (thyroid histology, pituitary cytology, and metabolic functions of the thyroid gland), the conclusion is drawn that a single injn. of 18 microcuries of I131 can be safely used as a tracer for metabolic studies in the adult rat. Evidence is presented to show that the changes occurring in the anterior pituitaries of rats after the injn. of large amts. of I131 are not the result of radiation damage to the pituitary itself but solely the consequence of thyroid destruction. The injn. of 300 microcuries of I131 resulted in considerable'' thyroid destruction, but 5-8 mos. later, normal glandular function was regained as judged by a study of the anterior pituitary. It is shown here, from a study of the reactions in the anterior pituitary, that the atypical thyroids present 6-8 mos. after single injns. of 525 microcuries of I131 synthesize negligible amts. of thyroxin or none at all. The cytological changes occurring in the anterior pituitary after the injn. of 875 microcuries of I131 are identical with those occurring after total surgical thyroidectomy.