A comparative study of iodine uptake by thyroid and thymus glands of male and female Sprague-Dawley rats of different ages.

The iodine concentrating ability of thyroid glands, thymus gland and skin in Sprague-Dawley rats was assessed by determining the tissue/blood radioiodide concentration ratios. Tissue/blood ratios are significantly affected by the age of the rats, however, thymus/blood radioiodide ratios never exceeded unity. The comparative uptake of 131I by thymus and thyroid tissue expressed as thymus/thyroid (%) for neonate animals was 10-16 times greater than those obtained for older rats. Moreover, the fraction of injected dose of radioiodide in thymus tissue never exceeded that of the thyroid or skin and paralleled the concentration of radio-activity in the blood. These results indicate that although neonate thymus tissue contains a significantly greater amount of radioactivity than the thymus of older rats, an active iodide concentration mechanism is not involved.