Possible Interaction: Iodides and Triiodothyronine

“This decrease in the serum T3 concentration after IA administration is due primarily to inhibition of peripheral 5-monodeiodination of T4 and, possibly, to a direct inhibitoy effect of excess iodide on the release of T3 from the thyroid.”

“These data suggest that: (1) Tg … under TSH control; (2) iodide … T3 release without affecting Tg secretion; (3) thyroidal injury results in marked increases in serum Tg concentrations; and (4) initial … may be useful in predicting remission in patients with hyperthyroidism due to Graves’disease treated with antithyroid drugs.”

“ Iodide induced small but highly significant decreases in basal serum T4 (8.0+/-… vs. 6.6+/-1.7 mug/100 ml; mean +/- SD) and T3 (128+/-15 vs. 110+/-22 ng/100 ml) and increases in basal … TSH (1.3+/-0.9 vs. 2.1+/-1.0 muU/ml).”

“ABSTRACT A 15-yr-old male is described who developed triiodothyronine thyrotoxicosis following pharmacological doses of iodide.”

“ Iodide accumulation was decreased by up to 40% after incubation with dexamethasone and T3 , respectively, in a concentration-dependent manner.”

“ T3 alone had no effect on iodide uptake, but attenuated iodide uptake stimulated by TSH.”

“ T3 was more potent in inhibiting TSH-stimulated iodide uptake than in enhancing TSH-stimulated DNA synthesis.”

“ Iodide concentrations of 10(-4) M or greater inhibited iodothyronine synthesis and thyroid hormone secretion, assessed by both assay of trichloroacetic acid-insoluble Na125I activity in cells and RIA of T4 and T3 in the medium and cell layer.”

“… T3 from … concomitant iodide production by cultured rat hepatocytes during a 20-h incubation in the presence of ER-22 were both inhibited by 50% with respect … incubation in the absence of monoclonal antibody, pointing to the importance of carrier-mediated transport in cellular uptake and metabolism of T3.”

“Therefore the pH dependency, rT3 and iodide may regulate the availability of T3 or rT3 depending on the metabolic requirements of thyroid hormones.”

“It is concluded that in addition to its inhibiting effect on thyrotrophin production T3 can also interfere with thyroidal iodide concentrating by another mechanism involving the pituitary in a mediating or permissive capacity.”