On the relation between thyroid depression and pituitary tumor induction in mice.

The development of tumorous growths in the pituitary glands of mice following the injection of radioiodine and subsequent radiothyroidectomy was first reported by Gorbman (8), who reasoned that thyroid destruction was not the principal fac tor in the production of these growths, since pitui tary tumors had not been induced when the thy roid gland was chronically depressed by goitrogens. Later, Gorbman (10) and Gorbman and Edelmann (11) obtained findings on which they based the conclusion that the radioiodine must act in a dual rule—indirectly by damaging the thyroid gland, and directly through some unexplained ef fects of its radiation on the treated mice. Moore, Brackney, and Bock (15) attempted to test this hypothesis by prolonged treatment with propyl thiouracil and by surgical removal of the thyroid gland. By the first procedure they produced evi dence that tumors can be induced in the unirradiated pituitary gland. Tumors were not produced by surgical thyroidectomy; however, considerable residual, functioning thyroid gland tissue was found at necropsy. In the present paper, findings are presented indicating that near-complete surgi cal thyroidectomy will induce pituitary tumors in mice. In addition, observations made on the histological nature of thyroid damage at various lev els of radioiodine treatment are described, and the following questions are considered : (a) What is the minimal dose of radioiodine necessary to induce pituitary tumors? (b) Are the changes seen in radi ation-damaged thyroid glands identical with the senile changes described by Andrew and Andrew (1)? (c) What is the regenerative capacity of the thyroid gland after radiation damage or subtotal thyroidectomy? and (d) Will dependent pituitary tumors (3, 5) persist and grow in surgically thyroidectomi/ed mice? Also, data suggesting a sex variation in susceptibility to pituitary tumor in-