Potassium perchlorate

Thyroxine (T4) and tri-iodothyronine (T3) are major thyroid hormones, or iodothyronines, that are synthesized and released from the thyroid. Iodine plays an essential role in the synthesis of these hormones. Via the sodium-iodide symporter (NIS), which is a protein located on the basolateral membrane of the thyroid follicular cell, iodine is transported from the blood into the thyroid gland where it is oxidized to. Perchlorate (ClO4−) is the dissociated anion of potassium perchlorate that exerts an inhibitory effect on iodide uptake by the thyroid gland in the cellular level. Due to its similarity in ionic size and charge to iodide, perchlorate inhibits the sodium-iodide symporter (NIS) without being translocated into the thyroid follicular cell. The inhibition constant, Ki, is estimated as 0.4 µmol to 24 µmol. At therapeutic dosage levels this competitive inhibition decreases the entrance of iodide into the thyroid, resulting in less available iodide for hormone synthesis and, therefore, a decrease in T3 and T4 synthesis. When ambient iodine intake is low or iodide uptake is sufficiently inhibited, perchlorate is capable in inducing goiter and hypothyroidism from inhibited iodide uptake. At high doses of potassium perchlorate, reduced T3 and T4 levels may be accompanied by increased TSH levels via a negative feedback loop, affecting the thyroid, pituitary and hypothalamus.