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

Abstract

Pituitary tumors induced by radiothyroidectomy are composed of thyrotropes which proliferate in response to sustained deficiency of thyroid hormone. Irradiation of the pituitary plays no significant role in the induction of these tumors; pituitary tumors induced by total body irradiation have a different hormonal spectrum. Total or subtotal surgical thyroidectomy will also induce thyro-tropic tumors. Whereas the normal thyroid undergoes tremendous hyperplasia when stimulated by autonomous thyrotropic tumors, the thyroid damaged by ionizing irradiation and the thyroid remnants after subtotal surgical thyroidectomy fail to undergo an adequate compensatory hyperplasia. Primary thyrotropic pituitary tumors and 1st generation tumor grafts can be controlled by thyroid hormone; the antonomous variants, which arise in the course of subpassages, are not controlled by this hormone. Growth relationship of the thyroid and the thyrotropes is inverse. Formation of adenomas in the thyroid, with invasion of blood vessels and metastasis to lymph nodes, are common in thyroids of normal mice bearing autonomous thyrotropic tumors, but these changes are dependent on excessive amounts of thyroid-stimulating hormones and are not manifestations of a malignant growth.