INHIBITION OF THYROIDAL RADIOIODINE UPTAKE FOLLOWING INTRAVENOUS ADMINISTRATION OF THYROXINE TO NORMAL AND TO HYPOPHYSECTOMIZED ADULT SUBJECTS*

Abstract

Administration of a single dose of dl-thyroxine or l-thyroxine intravenously to euthyroid adult subjects results in a lessened ability of the thyroid to accumulate radioiodine. In most subjects, this effect appears within 1 day and is most marked at 7 days after injection of thyroxine. Diminished thyroidal radioiodine up-take persists for one or more weeks. The thyroidal radioiodine uptake was measured in 2 patients prior to and following hypophysectomy. A similarity in pattern exists between the depression of thyroidal radioiodine collection following thyroxine administration in euthyroid subjects and the decline in up-take observed in hypophysectomized patients and following experimental hypophysectomy in rats.