IN-VITRO HEPATIC THYROID-HORMONE DEIODINATION IN IRON-DEFICIENT RATS - EFFECT OF DIETARY-FAT

The effects of different dietary fats on thyroid indices were studied in weanling iron-deficient rats. Rats were fed one of five different d iets (safflower oil with a casein protein source, safflower oil with d efatted 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 signif icant 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 anima ls had the highest hemoglobin concentrations. Type of dietary fat affe cted plasma thyroxine (T4), but not plasma triiodothyronine (T3) or ra te of deiodination of reverse T3 (rT3). Iron deficiency decreased plas ma concentrations of T3 and T4 and increased in vitro hepatic rT3 deio dination, suggesting that the ID animals tend to metabolize thyroid ho rmones via deactivating pathways. The alterations in thyroid hormone m etabolism associated with iron deficiency are reversible with iron rep letion.