Interfering Substances and Transport Mechanisms
Tuesday, March 15, 2016 12:54:14 PM America/Denver
Iodine is present is all organs and tissues of the body, not just the thyroid gland. In target cells, the mechanism used to concentrate peripheral iodine involve an energy-dependent transport of one atom of iodine sandwiched between two atoms of sodium across the cell membrane(1).
In the Thyrocyte (cells of the thyroid gland), the sodium/iodide symporter (NIS) is located in the basolateral membrane. The peripheral iodide enters the thyrocyte via the symporter in the basal membrane and crosses the thyrocyte as iodide to exit the thyrocyte via the apical membrane transporter just prior to oxidation and organification (2). In the case of the symporter, iodide must bind to a site called the halide symporter binding site before cellular uptake. Goitrogens compete for these binding sites that may lead to goiter due to induced iodine deficiency. Goitrogens such as Fluoride and Perchlorate bind to the same site as iodine without being transported into the cell, so they are considered iodine transport inhibitors. Bromide and thiocyanate also attach to this binding site, but, in addition, they are transported into the cell preventing oxidation and organification of iodine. Without these steps, iodine is not active at the cellular level.
The iodine spot test is used before iodine supplementation is started. This test is used to determine the presence or absence of severe iodine deficiency. This test is a good indicator of dietary iodine intake.
The Iodine 24 hour loading test was developed to determine whole body iodine sufficiency. This test is based on research showing once all tissues of the body are saturated additional iodine will be excreted in the urine (3). A problem exists when a patient has symptoms of iodine deficiency yet the 24 hour load shows iodine sufficiency. This is probably caused by the presence of chemicals (goitrogens) in the body blocking iodine absorption into the cell thereby artifically increasing iodine excretion. Urinary Bromide and Fluoride can also be measured in the 24 hour sample.
The best way to determine the presence of a symporter defect is by doing a saliva/serum ration test (2). Another way is to compare the spot iodine results with the 24 hour results. If there is a very high excretion after the 24 hours loading (>90% of the 50mg iodine load) yet a very low spot number, you can determine that the iodine is absorbing from the gut yet unable to penetrate into the cell.
Research done by Drs. Abraham, Brownstein and Flechas has shown that symporter function can be repaired by using 3 grams of Vitamin C daily. Organification is facilitated by a combination of INositol hexanicotinate 500mg + Vitamin B-2, 100mg daily.
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