IODINE DEFICIENCY IN CATTLE - COMPENSATORY CHANGES IN THYROIDAL SELENOENZYMES

The trace elements selenium and iodine are both essential for normal t hyroid hormone metabolism. To investigate the relationships between th ese functions, heifers were maintained on iodine-deficient or iodine-s ufficient diets from mid pregnancy to term. in these heifers and their offspring the interrelationship between iodine and selenium was appar ent with the preferential 10- to 12-fold induction of the selenoenzyme , thyroidal type I, selenium-containing iodothyronine deiodinase activ ity by iodine deficiency. This was accompanied by two- to four-fold in creases in cytosolic glutathione peroxidase activity, probably reflect ing increased oxidative activity and metabolism in the thyroid gland i n response to iodine deficiency. The above selenoenzyme activities wer e not affected in liver, kidney, pituitary and brain by iodine deficie ncy. The results are consistent with a critical role for selenium in b oth the normal function of cattle thyroid and key enzymes to compensat e for the effects of iodine deficiency.