DNA measurements on cell nuclei of normal, proliferating and neoplastic thyroid tissues in rats.

Nuclear DNA content was measured in 3 normal, 9 hyperplastic and 16 neoplastic rat thyroid glands. Thyroid hyperplasia and tumor growth were induced after treatment of the animals with X-rays and methylthiouracil. In the control animals only diploid thyroid epithelial cells were observed. At the stages of diffuse and nodular thyroid hyperplasia, the total DNA content per nucleus indicated for a diploid chromosome number and only a few cells were hyperdiploid. In the thyroid adenomas and carcinomas a scattering of the diploid region and an increase in the number of hyperdiploid cells was found. Among the various types of thyroid tumors neither difference in the number of hyperdiploid cells, nor typical pattern of distribution of these cells in the histogram was found. The increased number of hyperdiploid cells in the hyperplastic and neoplastic thyroids suggest an increase in the proportion of the cells entering the cell cycle and does not indicate for appearance of a neoplastic stemline.