Growth of Pituitary Tumors Secreting TSH*

Destruction of the thyroid gland by I's' in mice is followed by the development of TSH (thyroid stimulating hormone)-secreting pituitary tumors (5, 11, 13). These tumors can at first be grafted only on mice similarly radiothyroidectomized and not on normal animals (5) ; thus, they are initially conditioned or dependent growths. The tumor cells gain autonomy in the course of passages, as mdi cated by their ability to grow in normal mice (6). In further subpassages in normal hosts, they grow even better in normal than in radiothyroidec tomized hosts. These findings are best explained by successive modification in cells of the pituitary from normal to autonomous type. The mechanism of induction of pituitary tumor by radiothyroidectomy @†̃s not known with cer tainty. It has been postulated that depression of the thyroid gland with depression in TH (thyroid hormone) secretion stimulates those cells of the hypophysis which control thyroidal function. The possibility that injury to the pituitary by radia tions, incidental to radiothyroidectomy, is a con tributing factor in the induction of pituitary tu mors has, however, not been excluded thus far (10, 12). This problem calls for studies of minimizing irradiation of the pituitary incidental to I's' treat ment or avoiding irradiation altogether by per forming surgical thyroidectomies. The quantita tive study of the interrelationship between thyroid function and pituitary growth reported in this paper aims to contribute to the understanding of the mechanism of induction of pituitary tumors and maintenance of their growth. It will answer the question whether dependency and autonomy are absolute or relative characteristics of tumors. Dependent and autonomon8 tumors.—The induc tion and transplantation and some salient char acteristics of the transplantable pituitary tumors have been described (5—7) . Dependent tumor cells (Fig. 2) (those requiring absence of the thyroid for