Effect of thyroid hormone replacement in iron-deficient rats

Abstract

To determine if the previously observed alterations in norepinephrine (NE) metabolism and resting metabolic rate in iron-deficient (ID) rats result from hypothyroidism, exogenous thyroxine (T4) and 3,5,3'-triiodothyronine (T3) were administered to ID rats in doses sufficient to normalize the plasma concentrations of these hormones, whereas other ID and control (CN) rats received placebo treatment. Resting oxygen consumption was approximately 25% higher in ID than CN rats; T4 but not T3 treatment alleviated this elevated oxygen uptake. The NE content of interscapular brown adipose tissue (IBAT), liver, and heart was 70-80% lower in ID than CN rats, and NE turnover in the same tissues was likewise 40-60% lower in ID than CN rats, with no systematic effect of either T3 or T4 treatment. Liver T(4)5'-deiodinase activity was 70% lower in ID than CN rats and increased with T4 but not T3 treatment. These experiments show that iron deficiency alters NE and energy metabolism in a way that is mostly independent of its effects on thyroid hormone metabolism.

Effects of administration of iron, iodine and simultaneous iron-plus-iodine on the thyroid hormone profile in iron-deficient adolescent Iranian girls

“…The present study explored the hypothesis that iron deficiency might impair thyroid metabolism, as previously reported in animal and human studies (Dallman et al, 1978, 1980; Chen et al, 1983;Beard et al, 1984Beard et al, , 1990aMartinez-Torres et al, 1984;Brigham and Beard, 1995). Our findings confirm that an improvement in iron status had a positive impact on serum concentrations of thyroid hormones in iron-deficient adolescent girls.…”

“…Few studies in humans have been carried out on this subject. Results of those studies show that in adults, iron deficiency is accompanied by reduced serum T4 and T3 as compared to healthy controls (Dillman et al, 1980;Martinez-Torres et al, 1984;Brigham and Beard, 1995). In addition, Zimmermann et al (2000a) and showed that iron supplementation improved the efficacy of iodized salt in goitrous children with iron deficiency.…”

“…Theoretically, severe iron deficiency could lower thyroperoxidase activity and interfere with thyroid hormone synthesis. Animal studies have documented that weanling rats fed iron-deficient diets have significantly lower T3 and T4 compared to rats fed adequate iron (Chen et al, 1983;Beard et al, 1984;Brigham and Beard, 1995). Recently Hess and co-workers (2002) showed that thyroid peroxidase activity is significantly reduced in iron deficiency anaemia.…”

“…Studies in animals and humans have shown that iron deficiency with or without anaemia impairs thyroid hormone metabolism. Nutritional iron deficiency has been shown to significantly lower the circulating levels of both thyroxine and triiodothyronine in rats (Chen et al, 1983;Beard et al, 1984;Brigham and Beard, 1995), and to reduce conversion of T4-T3 (Dillman et al, 1980). Iron deficiency also impairs thyroid metabolism in human studies.…”

The Relationship between Iron Deficiency and Thyroid Function in Chinese Women during Early Pregnancy

“…ID may affect thyroid metabolism by inducing alterations in the common hypothalamic-pituitary-thyroid (HPT) axis (2), reducing T3 binding to hepatic nuclear receptors (18) or through anemia and lowered oxygen transport, similar to thyroid impairment in hypoxia (19). ID may also impair the activity of hepatic T4-5′deiodinase, an enzyme responsible for the conversion of T4 to T3 (20), or the activity of thyroid peroxidase, which is irondependent and responsible for thyroid hormone synthesis (4). Meanwhile, iron supplementation improves thyroid function.…”