Iodine Uptake and Release in Rats

This method may be used in the context of repeated dose treatment, on satellite groups of rats which show changes in thyroid uptake of labelled iodine. It may be sufficient to determine radio-iodine uptake in controls and in the high-dose group. 

A modification of this method was previously used for evaluation of thyrostatic drugs, andresponds to inhibition of the iodine transport mechanism in the thyroid gland. 

For conventional drug evaluation, all rats were pre-treated with the same dose of radio-iodine (pre-loading). The release of 131-1 from the pre-loaded thyroid in rats is inhibited by treatment with thyroxin 

Male Sprague-Dawley rats weighing 180-240 g are fed a commercial laboratory with low concentrations of thyroid hormones, containing constant amount of unlabelled iodine. The animals are treated for at least seven days with the test compound to be evaluated, at a pharmacologically active dose determined by a previous biological studies. On the morning of the test day, rats are injected with a test dose of 131-1 (intravenously or intraperitoneally), and the concentration of radioactivity in the thyroid glands is measured after 1 1 hours. The blood concentration of 131-1 at these time points is measured, and the tissue to blood ratios are calculated for individual animals. 

Statistical evaluation depends on the experimental design for such studies with pre-labelling of the thyroid gland and release by thyroid stimulating drugs, or single dose uptake of radio-iodine into the pituitary of treated rats, for example after several days of exposure to a thyrostatic drug. 

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