Comparative effects of 131I and 132I on rat thyroid

140 rats, 60 days old, were intoxicated with 131I and 132I. The absorbed doses to the thyroid were 25 (groupA1) 59(B1) and 92 Gy(C1) for 131I, and 7(A2), 14(B2) and 29 Gy(C2) for 132I. One month after intoxication, half of each group was administered with 0.1% MTU in drinking water for 28 days. All animals were sacrificed two months after intoxication. The results showed that the products of length multiplied by width of thyroid follicles decreased significantly along with the increase of absorbed dose in all groups except A1 to which MTU was not administered. Both the weight of thyroid(W) and the ratio(R) of W to the body weight were of power function relationship with the absorbed dose. In groups to which MTU had not been given, the doses required for decreasing both W and R to 1/2 of their control values were greater in 131I-intoxicated rats than those in 132I-intoxicated rats by a factor of 10.3 whereas in groups administered with MTU the factor was 10.2. In all groups except A1 there were various pathological changes such as atrophy or even disorganization of follicles, epithelial degeneration, nuclear polymorphism and pyknosis, etc. These changes were more profound in 132I-irradiated thyroids than those in 132I irradiated ones. The results suggested that the destructive effect of 132I in thyroid was 9 times greater than that of 131I