Dependence of Protein-Binding of Iodide on Concentration of Thyroidal Iodide in Chickens

Chickens which had been fed either a control or low-iodine diet were injected with graded doses of stable iodide; concentrations of serum iodide and newly entered thyroidal iodide and protein-bound iodine were measured at the end of 1 hr. T/S[I-], ratio of the concentration of iodide in the thyroid to that in an equivalent amount of serum, was initially independent of concentration of serum iodide as the latter was increased from low levels, then increased by a factor of 15–25, and finally declined to a value of <1. The concentration of proteinbound iodine increased progressively as thyroidal iodide increased; a minor, statistically significant decrease (Wolff-Chaikoff effect) occurred at relatively high levels of thyroidal iodide in birds fed the low-iodine diet but not in the control birds. (Endocrinology85:231,1969)