Effect of graded doses of iodide on thyroid hormones in intact, thyroxine-treated and hypophysectomized rats

480 albino rats were used in the present study to see the effect of graded doses of iodide (low dose 10 micrograms/kg B. W. and high dose 1 mg to 30 mg/kg B. W.). On thyroid hormone status in intact, T4 treated and hypophysectomized rats. Serum free thyroxine and resin T3 uptake were estimated to assess thyroid function. Serum free thyroxine was calculated by multiplying serum total thyroxine and percentage free thyroxine. Low dose of iodide in case of 1) intact rats did not produce any change in thyroid status; 2) T4 treated rats showed significantly lower levels of serum free T4 and resin T3 uptake; 3) hypophysectomized rats exhibited extremely low levels of thyroid hormones. High dose of iodide in intact rats produced a low level of thyroid hormones and high dose iodide in T4 treated rats produced a hyperthyroid state. The result showed that iodide inhibition or stimulation at thyroid level depends upon the state of thyroid and the dose of iodide used.