Cell Population Kinetics during the Induction of Thyrotropic Pituitary Tumors¹

Changes in weight and in the incorporation of infused TdR-³H² thymidine into the DNA of the pituitary gland were determined at intervals during the development of thyrotropic tumors in radiothyroidectomized mice. The relative specific activity of the DNA was found to increase markedly during the final stage of tumor development. In an effort to correlate the information on the sequence of changes during tumor induction, 5 mathematical models of cell population changes were considered. A model that assumes persistence of most of the original cell population at a constant level throughout tumor induction, an exponential increase in the size of a cell population that initially constitutes a small percentage of the total population, and the appearance of a 3rd more rapidly increasing cell population some time after radiothyroidectomy was described. This model was found most consistent with the experimental data presented and with published results of others and may be an aid in the design of future experiments.