MICROSCOPIC DISTRIBUTION OF RADIOACTIVE IODINE, AND SIDE-EFFECTS OF THYROID PROTECTION IN IODINE-DEFICIENT NEWBORN RATS - INSIGHTS INTO THEAFTERMATH OF THE CHERNOBYL ACCIDENT

A dramatic increase in the incidence of childhood thyroid cancer was r eported after the Chernobyl accident. We used new-born rats to mimick the relative iodine deficiency prevailing in this area before the acci dent. Then, some animals received iodine 129, a radioisotope, and we s tudied the microscopic distribution of incorporated radioactive iodine in the thyroid. Analytical ion microscopy provided separate distribut ion images for each radioactive isotope and stable iodine. In other an imals we used light microscopy to study the adverse effects of stable iodine overload (a protective measure) on thyroid structure. We found that i) iodine deficiency in new-born rats induces marked heterogeneit y in the distribution of incorporated radioactive iodine and, hence, h eterogenous distribution of the radiation dose at the microscopic leve l, which could be an additional factor promoting tumorigenesis and ii) massive iodine overload has toxic effects on the thyroid of new-born rats, with necrosis and desquamation of epithelial cells.