Thallium-201 distribution in the thyroid: relationship to thyroidal trapping function.

Experiments were undertaken to determine the behavior of thallium-201 in the thyroid in relation to the iodide-trapping mechanism in rats. Iodide trapping was compared to thyroidal thallium-201 trapping 30 minutes after intravenous injection. Thallium-201 uptake followed iodide uptake in control rats. TSH- and T3-treated rats but did not decrease in the same manner as iodide concentration in perchlorate-treated rats. These studies suggest that thallium-201 distribution in the thyroid may reflect the cationic side of the iodide pump or possible thyroidal blood flow.