Tumor Induction in Hypophyseal Grafts in Radiothyroidectomized Mice;Hypothalamico-hypophyseal Relationships. ∗

Summary

Pituitary glands from intact or radiothyroidectomized mice were grafted beneath the kidney capsules of similar intact and radiothyroidectomized recipients in all 4 donor-host combinations in mice of both sexes and in castrated males. Tumors arose in high frequency in such grafts in intact and in thyroidectomized female LAF₁ mice irrespective of the pretreatment of the donors. Transplantation assays indicated that the tumors arising in such grafts were most probably not thyrotropic in nature, but rather were mammotropic, regardless of the treatment of the first host. In contrast, the tumors arising in the thyroidectomized host pituitaries in situ were typically thyrotropic in behavior. No tumors were found in sub-capsular pituitary grafts in intact or gonadectomized C57Bl/6 male mice, and a small mass (5.5 mg) of as yet unknown character was found at the graft site in but one of 18 thyroidectomized males. The pituitary glands in situ of all of the thyroidectomized males were, however, tumorous. It is tentatively concluded that immediate circulatory connection with the hypothalamus is important in, and probably essential to, the induction of dependent thyrotropic tumors. The possibility that the cells capable of thyrotropic tumor formation did not survive the transplantation seems much less likely. The transformation of a normal thyrotropic cell into a dependent tumor cell thus appears to involve a change in the requirement for, or response to, hypothalamic factors. The role of hypophyseal irradiation in induction of thyrotropic piutitary tumors by radiothyroidectomy with I¹³¹ was not further clarified.