Effect of selenium depletion and supplementation on the kinetics of type I 5′-iodothyronine deiodinase and T3/T4 in rats

Presently, the effect of selenium (Se) deficiency and excess of Se (1 ppm) on the activity of selenoenzymes type 1 5'-iodothyronine deiodinase (5'-DI), glutathione peroxidase (GSH-Px), and level of thyroid hormones (T-3 and T-4) was studied in rats. Se levels in the serum and liver, T3 and T4 in the serum, GSH-Px levels in the liver, and 5'-DI activity in the liver/aorta/thyroid were estimated after 1, 2, and 3 mo of Se-deficient (0.02 ppm), Se-adequate (0.2 ppm), and Se-excess (I ppm) diet feeding. All of these parameters decreased significantly in the Se-deficient group as compared to the adequate group. Within the deficient group, as the Se deficiency progressed, all of the parameters except 5'-DI decreased after 2 and 3 mo in comparison to 1-mo data. Thyroidal 5'-DI activity in Se deficiency showed the maximum increase. A significant increase was observed in all of the above parameters in the 1 ppm Se-supplemented diet group when compared with the adequate Se group; also, as the Se deposition increased within the Se-excess diet group, a significant increase was observed in all of the above parameters. However, as observed by others, the intake of excess of Se (i.e., 2 ppm in the diet) did not elevate the activities of selenoenzymes and thyroid hormones; rather, it had adverse effects. The present study concludes that Se supplementation at least up to 1 ppm enhances the selenoenzyme activities, and above this level, it may not be considered as an indicator of selenoenzyme activities.