THE INFLUENCE OF THE THYROID GLAND ON IODIDE TOLERANCE IN RABBITS1

Abstract

Iodide tolerance tests, as used in this investigation, measure the rate of loss of intravenously injected iodide from the blood of rabbits. A known quantity of KI is injected into a marginal ear vein and 1 cc. samples of blood are withdrawn by heart puncture at given intervals thereafter and analyzed for iodide content. Since the thyroid becomes saturated with iodide very rapidly following iodide adm., the first 30 min. of the test are emphasized. After the inj. of from 2 to 8 mg. of iodide, the rate of iodide loss from the blood is uninfluenced by thyrotrophic-induced thyroid hyperplasia or athyroidism. Tolerance curves obtained after inj. of small quantities of iodide (0.075 mg.) are markedly affected by these conditions. In rabbits with hyperplastic thyroids, the plateau of the tolerance curve is reached in 1 or 2 mins. after iodide inj. This may be compared with 5-10 min. for normal rabbits and 20-30 min. for thyroidectomized animals. The shapes of these curves indicate that the thyroid gland has a high affinity but limited capacity for iodide and that the blood iodide changes occurring during the first 30 min. of an iodide tolerance test are of greater significance than those occurring later.