Abstracts Biological Sciences

The role of iodine deficiency and radiations in the production of thyroid tumors in the rat.

by Mansukhlal G. Mandavia

Tumors of the follicular cells of rat thyroid glands were produced with the intent of exploring the respective roles of radiations and hyperplasia. Such tumors, which can be malignant, were induced by x-irradiation, radioactivity, or prolonged low-iodine diet, alone or in combination. Thyroid glands were examined in serial sections; and, quantitative data were obtained on the incidence of tumor-bearing animals, the number of tumors per gland, and the total volume of tumors per gland. Hyperplasia, associated with low-iodine diet, induced in six to twelve months a greater yield of tumors than did radiations in the doses employed. However, when radiation was followed by hyperplasia, the yield was much more than expected by a simple additive effect of these two factors. The interpretation is that in carcinogenesis of the thyroid, radiation acts as an 'initiating' agent, whereas hyperplasia acts as a promoting agent (possibly also as an 'initiating' agent).