In vitro hepatic thyroid hormone deiodination in iron-deficient rats: Effect of dietary fat

Abstract

The effects of different dietary fats on thyroid indices were studied in weanling iron-deficient rats. Rats were fed one of five different diets (safflower oil with a casein protein source, safflower oil with defatted beef as the protein source, prime rib, beef tallow with casein and stearate with casein). Both dietary fat and iron status (adequate, CN; deficient, ID; or iron-deficient replete, ID-replete) had significant effects on body weight and hemoglobin concentrations. The tallow-fed animals weighed the least relative to animals fed the other fats; ID rats were smaller than CN rats. The tallow- and stearate-fed animals had the highest hemoglobin concentrations. Type of dietary fat affected plasma thyroxine (T 4), but not plasma triiodothyronine (T 3) or rate of deiodination of reverse T 3 (rT 3). Iron deficiency decreased plasma concentrations of T 3 and T 4 and increased in vitro hepatic rT 3 deiodination, suggesting that the ID animals tend to metabolize thyroid hormones via deactivating pathways. The alterations in thyroid hormone metabolism associated with iron deficiency are reversible with iron repletion.