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Selenium Requirements of Rats for Normal Hepatic and Thyroidal 5'-Deiodinase (Type I) Activities¹

Division of Human Nutrition, Department of Preventive Medicine and Community Health, The University of Texas Medical Branch, Galveston, TX 77555-1009

The nutritional requirement of selenium for type I 5'-deiodinase activity in thyroid compared with liver was assessed in rats. Male weanling Sprague-Dawley rats were fed a torula yeast-based diet for 20 wk. One group of rats was fed the Se-deficient basal diet (0.01 mg Se/kg). The other three groups were fed the basal diet plus sodium selenite at 0.05, 0.1 and 0.5 mg Se/kg diet. Liver 5'-deiodinase and glutathione peroxidase (GSH-Px) activities were depressed in the group fed the Se-deficient (basal) diet compared with the other groups. Liver 5'-deiodinase activity in the group fed 0.05 mg Se/kg diet was as high as in the groups fed 0.1 and 0.5 mg Se/kg diet, whereas GSH-Px activities in the groups fed 0.05 and 0.1 mg Se/kg diet were intermediate in value. Feeding the Se-deficient diet for 20 wk did not cause a suppression in 5'-deiodinase in the thyroid, and thyroid GSH-Px activity was -40% of that in the other groups. In rats fed Se-supplemented diets, thyroid GSH-Px was -20% or less of the activity found in liver. Plasma thyroxine was higher in the group fed the Se-deficient (basal) diet, but there were no differences in plasma 3,3',5-triiodothyronine among all groups. The results suggest that the nutritional Se requirement for 5'-deiodinase is less than that for GSH-Px and is -0.05 mg Se/kg in the diet for normal activity in the liver and -0.01 mg Se/kg for normal activity in the thyroid. Thyroid seems to be a priority organ over liver for Se when the intake of the element is limited.

KEY WORDS: • selenium • 5'-deiodinase • glutathione peroxidase • rats • thyroid hormones

¹ Supported by a grant (DK 14184) from the National Institutes of Health.

² To whom correspondence should be addressed.

Manuscript received 28 September 1992. Revision accepted 11 January 1993.