INCREASE OF SERUM FREE THYROXINE FOLLOWING THE ADMINISTRATION OF THIOCYANATE AND OTHER ANIONS IN VIVO AND IN VITRO

Abstract

ABSTRACT Following the addition of thiocyanate (SCN−) to human and rat serum of 80 mg SCN−/ 100 ml (initial concentration before dialysis) a marked increase in serum free thyroxine (FT4) was found. The addition of equivalent doses of other antihyroid anions or permanganate showed a similar increase of FT4 in the order: BF4− < CIO4− = SCN− < MnO4−. The increase in the rat serum was greater than that in human serum. After peroral administration of these anions to the rats in amounts equal to 30 mg SCN−/rat the increase of FT4 was still higher. The addition of increased doses of SCN− to the human and rat sera (5-80 and up to 1600 mg SCN−/100 ml) caused a linear increase of FT4. Similarly, after the administration of various doses of SCN− to rats (5-30 mg SCN−/rat) a linear dose-response of the FT4 level in serum was observed. The time-course of the increase of % FT4 and absolute FT4 (AFT4) level after a single administration of SCN− to rats coincided with the increase of the serum SCN− level. However, after the disappearance of SCN− from the serum the % FT4 returned to the initial value, while the AFT4 was decreased. The effect of these anions probably consists in the competitive displacement of thyroxine from serum thyroxine-binding proteins. These and previous results suggested that thiocynate influences the plasma protein-thyroxine equilibrium and the possible role of an increased free thyroxine level on the action of thyroxine on various tissues and the hypothalamo-pituitary-thyroid feed-back is discussed.