Effect of Thyroid Hormone on Growth of Thyrotrophin-Secreting Pituitary Tumors. ∗

Abstract

Summary and Discussions

1. The administration of thyroid hormone effectively prevents the growth of dependent pituitary tumors induced in and grafted on radiothy-roidectomized mice. Autonomous pituitary tumors grow faster in normal than in radio-thyroidectomized hosts, and, in the latter, administration of TH hastens the growth of the tumor. Sustained thiouracil treatment does not render normal mice susceptible to dependent pituitary tumors but hastens somewhat the growth of such pituitary tumors which tend to become autonomous. 2. These experiments support the view that lack of TH is the major growth stimulant of pituitary growths in radiothyroidectomized mice and that sustained lack of this hormone is essential for the proliferation of these tumor cells. In the course of sustained proliferation a new (autonomous) type of tumor cell arises which is not only uninhibited but is often stimulated by TH, the physiological depressant of normal pituitary cells producing thyrotrophin.