THE MECHANISM OF INDUCTION AND THE CHARACTERISTICS OF PITUITARY TUMORS INDUCED BY THYROIDECTOMY*†

Abstract

DESTRUCTION of the thyroid by radioiodine gives rise to pituitary tumors in all strains of mice thus far tested (1–4). Sustained deficiency of thyroid hormone (TH) leads to hyperplasia of pituitary cells secreting thyroid-stimulating hormone (TSH), followed by the development of tumors that are responsive to the restraining force of TH. Transplantation of pituitary tumors induced by thyroidectomy succeeds only in mice with thyroids which have been destroyed by I131 or removed surgically. These tumors grow also in hosts subjected to subtotal thyroidectomy, but after a longer latent period and at a slower rate. The relation of proliferation of thyrotropic tumor cells to thyroid function is inverse and quantitative (5). In the course of continued subpassages in mice these dependents tumors give rise to autonomous variants. The autonomous tumors grow better in normal than in athyroid hosts. Part of the work surveyed here has already been reported (3–7), and part will be described later (8, 9). This report is a summary of all relevant observations which have led us to the conclusion that sustained deficiency of thyroid hormone gives rise to thyrotropic pituitary tumors, whether the thyroid deficiency be brought about by ionizing radiation or by other agents.