Studies on the Pathogenesis of Colloid Goiter

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Abstract
Hyperplastic goiters were produced in rats by feeding a low-iodine diet (LID) or LID combined with 0.15% propylthiouracil (PTU). The animals were fed LID either continuously, or cyclically with alternate feeding of a high-iodine diet of Purina Lab Chow for varying periods of time. Refeeding a high-iodine diet after a hyper-plastic goiter had been present for only a short time resulted in return of the thyroid gland to normal or near-normal size within 2 weeks. Thyroid histology also reverted to a normal appearance, the follicles becoming refilled with colloid and the epithelial cells changing from high cuboidal or columnar to flat or low cuboidal. If the hyperplastic goiters had been present for several weeks or months, the same changes in thyroid histology were produced, but the thyroid always remained at least 2-3 times normal size even up to 12 weeks after refeeding a Purina diet. Large iodine supplements did not reduce thyroid size or alter the hyperplastic appearance of the thyroid of animals maintained on PTU. Changes nearly identical with those produced by refeeding a high-iodine diet followed hypophysectomy, even if the rats were maintained on LID or LID-PTU. It is concluded that the most important etiologic factor in the production of colloid goiter is a reduction of TSH [thyroid-stimulating hormone] stimulation of a thyroid gland previously hyperplastic for a prolonged period of time.