Inhibition of hepatic deiodination of thyroxine is caused by selenium deficiency in rats

Abstract

Selenium (Se) deficiency produced up to a 14-fold decrease in hepatic tri-iodothyronine (T3) production from thyroxine (T4) in vitro. The T3 production rate could not be restored by the addition of a variety of cofactors, nor by the addition of control homogenate. The impairment in hepatic T3 production observed in Se deficiency was reflected in the concentrations of thyroid hormones circulating in plasma, T4 being increased approx. 40% and T3 being decreased by 30%. However, the fall in plasma T3 concentrations was smaller than might be expected in view of the marked decreased in T3 production. Se deficiency had no measurable effect on plasma reverse-tri-iodothyronine concentrations. The data suggest that Se deficiency produces an inhibition of both 5- and 5'-deiodination, consistent with the widely held view that these reactions are catalysed by the same enzyme complex. The mechanism of inhibition appears not be mediated by changes in thiol levels, but a direct role of Se in the activity of the deiodinase complex cannot be excluded.

Selenium and Iodine Status of two Camel Breeds (Camelus Dromedaries) Raised Under Semi Intensive System in Saudi Arabia

“…It is well documented in the literature the correlation between Se and thyroid hormones since Se is required for conversion of thyroxine (T4) to active triiodothyronine (T3) as a main component of type 1 deiodinase (Beckett et al, 1987;Awadeh et al, 1998).…”

“…They stimulate protein synthesis, increase adipose tissues lipolysis and blood glucose (Chatterjea and Shinde, 2005;Todini, 2007). Selenium is well known to affect thyroid hormones functions as a main component of type 1 deiodinase, which is needed to convert thyroxine (T4) into the more active triiodothyronine (T3) hormone (Beckett et al, 1987). Both selenium and iodine deficiencies are recognized as global problem which affect animal and human health.…”

Supplementing selenium yeast to diets with adequate concentrations of selenium: Selenium status, thyroid hormone concentrations and passive transfer of immunoglobulins in dairy cows and calves

“…Type I iodothyronine deiodinase is a Se-dependent enzyme that catalyzes the 5? deiodination of T 4 to the more metabolically active T 3 (Beckett et al 1987;Berry et al 1991). A deficiency of Se reduces the activity of the type I iodothyronine deiodinase and impairs T 3 production, which is reflected in the circulating plasma thyroid hormone concentrations as a reduction in the T 3 concentration and an increase in the T 4 concentration (Beckett et al 1987;Arthur et al 1990).…”

“…deiodination of T 4 to the more metabolically active T 3 (Beckett et al 1987;Berry et al 1991). A deficiency of Se reduces the activity of the type I iodothyronine deiodinase and impairs T 3 production, which is reflected in the circulating plasma thyroid hormone concentrations as a reduction in the T 3 concentration and an increase in the T 4 concentration (Beckett et al 1987;Arthur et al 1990). In growing calves fed Se-deficient diets from weaning to 3 mo of age, plasma T 3 concentrations were decreased and plasma T 4 concentrations increased compared with Sesupplemented calves (0.015 vs. 0.1 mg Se kg (1 ; Arthur et al 1988).…”

“…Glutathione peroxidase was the first selenoenzyme identified (Rotruck et al 1973) and is well recognized for its role in the antioxidant defense system that protects membrane integrity and the oxidation of biomolecules. Selenium also functions at the active site of enzymes involved in the production and regulation of thyroid hormones (Beckett et al 1987) and is recognized for its role in immune function (Arthur et al 2003).…”