Transplantable thyroid tumors in the rat: development of normal-appearing thyroid follicles in the differentiated tumors, and development of differentiated tumors from iodine-deficient, thyroxine-involuted goiters.

entiated tumors. The first-generation transplantable tumors are usually differentiated, functional, and thyrotropin dependent. The tumors of later generations are often poorly differentiated, nonfunctional, and thyrotropin independent. Williams and Doniach (15) observed growth of thyroid autotransplants in hypophysectomized rats and in rats with thyrotropin secretion suppressed by administration of large doses of thyroxine. This approach has not been used in the investigation of transplantable thyroid tumors. Leblond and Isler (8) demonstrated that feeding of iodine caused involution of thyrotropin-dependent (3-nodules of iodine-deficient goiters in rats, while autonomous v-nodules increased in size and number. This phenomenon also has not been examined in the development of transplantable thyroid tumors. In such an experiment thyroxine could be sub stituted for iodine. This is a report of experiments designed to examine the development of transplantable thyroid tumors in rats by transplantation of iodine-deficient thyroid tissue containing a thyroid tumor into the normal animals fed a regular diet and by transplantation of iodine-deficient, thyroxine-involuted thyroid tissue into thyroidectomized rats fed an iodine deficient diet.