THE BIOLOGIC EFFECT OF IRRADIATION BY RADIOACTIVE IODINE*†

Abstract

The radiation effect of radioactive iodine (I131) in doses of 1, 10, and 50 microcuries on various functions of the thyroid was studied in cockerels. Detn. of thyroid collection curves for 0.5 [mu]c, 1 [mu]c, 10 [mu]c. and 50 [mu]c. demonstrated a consistent similarity during the first 96 hrs. The earliest radiation effect was observed after 144 hrs. in the animals which received 50 [mu]c. and indicated that the thyroid cannot retain a large dose of I131 as well as it does a smaller one. Thyroid growth was inhibited by doses of 10 [mu]c. and 50 [mu]c. Iodine concn. was normal after 10 [mu]c but decreased after 50 [mu]c. No effect of 1 [mu]c. was noted on growth and iodine concn. The response to thiou-racil was inhibited after admn. of 50 [mu]c Response to thyro-trophic hormone as measured by increase in thyroid wt. and loss of thyroid I was normal in all radiated animals 16 days after admn. of I131 but after 24 days there was a dissociation in response between the 10 [mu]e. and 50 [mu]c group. The 10 [mu]c caused an iodine loss but no increase in thyroid wt. 50 [mu]c.had no effect on thyroid wt. and the loss of I was minimal.