These include interference with enterohepatic circulation of thyroxine (17), competition with thyroid hormones for thyroid sulfotransferase enzymes (18), inhibition of thyroid peroxidase (19) and interference with thyroid hormone synthesis by inhibition of iodide uptake and organification
5) Therefore, drugs that inhibit the organification
process are not as successful in type II AIT, and glucocorticoids are more often used.
Methimazole works by blocking the organification
of iodide, which decreases thyroid hormone production.
The process whereby iodine is incorporated into the thyroid hormone is known as organification
defects are associated with mutations in the TPO or DUOX2 genes (22-25) and are characterized by a positive perchlorate discharge test.
Twelve patients (36%) were diagnosed with dyshormonogenesis, which consisted of an organification
defect in all but one patient.
Vulsma T, Gons MH, de Vijlder JJM, 1989, Maternal-fetal transfer of thyroxine in congenital hypothyroidism due to a total organification
defect or thyroid agenesis, N Engl J Med 321(1):13-16, Wilber JF, Utiger RD, 1969, The effect of glucocorticoids on thyrotropin secretion, J Clin Invest 48(11):2096-2103.
It inhibits iodide transport and organification
as well as increasing the efflux of iodide from the gland.
The results of the above study (4) do not support implication of thiocyanate (as shown by I/SCN ratios in urine), while possibility of other goitrogens which interfere with organification
and coupling, needs further investigation.
2] production is evidenced by the fact that antioxidants used in Bagchi's experiments did not interfere with the oxidation and organification
of iodide and therefore neutralized only the excess oxidant.
Other causes are surgical removal of the thyroid gland, radioactive iodine thyroid gland ablation, external irradiation and a thyroid gland iodine organification
The laboratory method for assessing iodide organification
is the perchlorate discharge test, which produces a marked decline in the radioiodine content of the thyroid gland (to [less than or equal to] 10% of baseline value).
An increased organification
of thyroidal iodide for the synthesis of thyroid hormones by the ATP cofactors could explain this effect on thyroid hormones.