Sodium selenite enhances thyroid uptake of iodine-131 and regulates thyroid function in rats.

The aim of the present study was to evaluate the role of selenium (Se) on the thyroid uptake and retention of radioiodine ((131)I) and on the serum levels of thyroid hormones. Experimental rats were divided into four groups with 10 animals in each group viz: untreated controls, (131)II-treated, Se-treated and (131)I+Se-treated. Group II and Group IV animals were injected intraperitoneally with 3.7MBq of (131)I. Group III and Group IV animals received Se in the form of sodium selenite, everyday at a dose of 1ppm in drinking water. Thyroidal (131)II uptake measurements, determination of biological half life of (131)I and estimation of serum of tri-iodothyronine (T3) and tetra-iodothyronine (T4) and thyroid stimulating hormone (TSH) were carried out at two time intervals after 2 and 4 weeks. The statistical significance of the data was determined by using one-way analysis of variance (ANOVA) followed by Newman-Keuls test. The results showed lower serum levels of T3 and T4 and higher TSH levels in rats treated with (131)I when compared to untreated rats. Furthermore, the biological half life (Tbiol) of (131)I in thyroid and thyroidal (131)I uptake values at 2h and 24h were significantly lower in rats treated with (131)I compared with untrated control. Selenium treatment of (131)I treated rats resulted in a significant increase in the thyroid uptake as well as Tbiol of (131)I which indicated its increased retention. Moreover, normalization of the elevated serum TSH levels and a significant increase in the T3 and T4 levels was evident when Se was administered to the (131)I treated rats. In conclusion, this study indicates that Se when given to rats in the form of sodium selenite, at a dose of 1ppm in drinking water enhances the uptake and retention of (131)I in the thyroid as well as regulates thyroid hormone levels.