Transport of radioiodide between thyroid gland and blood in mice and rats

Abstract

Equilibration data were obtained for thyroids of various activities in rats and mice given a single dose of propylthiouracil to block organic binding of radioiodine. Data were compared with an open two-compartment model of the thyroid characterized by a one-way thyroid clearance of serum radioiodide and an exit rate constant for the transport of radioiodide from the thyroid to the blood. The model generally fitted the data within experimental error. Clearances increased with thyroid activity. Exit rate constants were much larger for animals fed thiouracil than for other animals. Thiocyanate increased the exit rate constant but did not change the thyroid clearance of serum radioiodide significantly. A new open three-compartment thyroid model was introduced and was used to explain how thiocyanate could increase the exit rate constant by inhibiting the transport of iodide from the follicular cells to the lumen of the follicle.