Transport of radioiodide between blood and thyroid of chickens

Abstract

Experimental data concerning the increase in T/S[I-] (ratio of concentration of radioiodide in thyroid to that in serum) during equilibration following a single injection of radioiodide were obtained from chickens in which organification of iodide was previously blocked by a single injection of methimazole. Equilibration data were obtained from control chickens as well as from chickens which had been treated with a low-iodine diet, high-iodine diet, thiouracil in feed, thyroxine injections, or a single injection of thiocyanate. The data were compared with predictions based on the open two-compartmental model of Wollman and Reed (Am. J. Physiol. 196: 113-120, 1959). Thyroidal clearance constants (C/m) for radioiodide varied considerably with experimental treatments. Exit rate constants (KTB) were relatively more stable about a control value of 0.035 min-1 except after a single injection of thiocyanate wherein KTB increased to 0.26 min-1. Data concerning the dependence of T/S[I-] on serum iodide concentration were analyzed with the aid of modifications of an empirical equation (Am. J. Physiol. 186: 453-459, 1956). Km was found to be 0.35 mg iodide/100 ml serum. Predictions based on the models fit the experimental data from chickens reasonably well.