SELENIUM AND IODINE DEFICIENCIES - EFFECTS ON BRAIN AND BROWN ADIPOSE-TISSUE SELENOENZYME ACTIVITY AND EXPRESSION

Adequate dietary iodine supplies and thyroid hormones are needed for t he development of the central nervous system (CNS) and brown adipose t issue (BAT) function. Decreases in plasma thyroxine (T-4) concentratio ns may increase the requirement for the selenoenzymes types I and II i odothyronine deiodinase (ID-I and ID-II) in the brain and ID-II in BAT to protect against any fall in intracellular 3,3',5 tri-iodothyronine (T-3) concentrations in these organs. We have therefore investigated selenoenzyme activity and expression and some developmental markers in brain and BAT of second generation selenium- and iodine-deficient rat s. Despite substantial alterations in plasma thyroid hormone concentra tions and thyroidal and hepatic selenoprotein expression in selenium a nd iodine deficiencies, ID-I, cytosolic glutathione peroxidase (cGSHPx ) and phospholipid hydroperoxide glutathione peroxidase (phGSHPx) acti vities and expression remained relatively constant in most brain regio ns studied. Additionally, brain and pituitary ID-II activities were in creased in iodine deficiency regardless of selenium status. This can h elp maintain tissue Tg concentrations in hypothyroidism. Consistent wi th this, no significant effects of iodine or selenium deficiency on th e development of the brain were observed, as assessed by the activitie s of marker enzymes. In contrast, BAT from selenium- and iodine-defici ent rats had impaired thyroid hormone metabolism and less uncoupling p rotein than in tissue from selenium-and iodine-supplemented animals. T hus, the effects of selenium and iodine deficiency on the brain are li mited due to the activation of the compensatory mechanisms but these m echanisms are less effective in BAT.