Further studies on induction and growth of thyrotropic pituitary tumors in mice.

The induction of tumors of the adenohypophysis in mice by radiothyroidectomy (Gorbman [8]) has been amply confirmed. These tumors are thyrotropic (4). They are initially transplantable only to hosts whose thyroid function has been depressed by either radiothyroidectomy or surgical thyroidectomy; but autonomous strains have been developed after subpassages of most of the originally dependent lines (~, 7). Whether or not radiation is essential to the induction of these tumors is controversial (~, 8). Our view that radiation is not essential is based on their having been induced by surgical thyroidectomy (2) and by sustained treatment with large dosages of propylthiouracil (10, 11). Induction of pituitary tumors by propylthiouracil has not been thus far confirmed, and the published experiments on their induction by surgical thyroidectomy (2) are not entirely conclusive. The thyroidectomized animals (2) received a diagnostic dose of radioiodine administered to ascertain the completeness of thyroidectomy. The dose used (5-9 ~c. of 1131) is too small to induce pituitary tumors in normal mice, the threshold dose for tumor induction being ~5 ~c. in females and somewhat more in males. It is conceivable, however, that this dose of 1131 exerted some co-carcinogenic effect on the pituitaries of mice whose thyroids were subtotally or completely resected. It seemed desirable, therefore, to repeat this experiment entirely avoiding the use of I ~81. A closely related line of investigation involves the growth of transplanted dependent tumors. Since they had been shown to proliferate in surgically, as well as in radiologically, thyroidectomized hosts (~, 4), it seemed probable that they would also grow in hosts whose thyroids had been blocked