Endocrine Abstracts (2004) 7 P237

Seaweed as a model for iodide uptake and retention in the thyroid

E Burbridge, C Clarke & PPA Smyth

Conway Institute of Biomolecular and Biomedical Research, Dublin, Ireland.

Uptake of ingested iodide (I-) in the thyroid is achieved through an active transport system, the sodium iodide symporter (NIS). The gland has the ability to accumulate I- from the bloodstream by a factor of 20-40. Seaweeds, which in vivo bear the same relationship to seawater, as does the thyroid to the bloodstream, have a dramatically more efficient I- uptake system, accumulating I- from seawater by a factor of anything up to 1 million. The objective was to extract iodine from commonly used Irish seaweeds and to determine it's effect on I- uptake in the rat thyroid FRTL-5 cell line. Iodine content of seaweeds was measured using an alkaline ashing method and quantified colourimetrically using the Sandell-Kolthoff reaction. The results presented are based on the use of the seaweed Laminaria digitata which was found to have a total iodine content of 3356 milligrams per litre. Cells were incubated with KI or seaweed extracts (of equivalent iodine concentration) in the range of 0 to10 millimolar for uptake studies and 0 to 1mM for efflux studies. Radioiodide uptake decreased from 10-90 percent when treated with KI. While seaweed, extracts showed an increase of radioiodide uptake at low iodine levels in comparison to KI. The percentage of iodide retention was increased by 25% in the presence of seaweed extracts. These findings illustrate both iodide uptake potentiating, blocking and retention effects in cells treated with seaweed extracts and raise the possibility of incorporating 125I in seaweed for ablative therapeutic use. We could conclude from uptake studies that seaweed may present a more bioavailable form of iodide and therefore may be important to note that consumption of seaweeds can result in a significant increase in dietary iodine intake, which if chronically ingested, has been shown to can lead to hyperthyroidism.

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