Effects of a selenium deficient diet on thyroid function of normal and perchlorate treated rats

Abstract

Pregnant rats were submitted to a selenium\x=req-\ deficient diet immediately after mating; it was continued for 4 weeks after delivery. The pups were sacrificed at 3 and 4 weeks of age. Perchlorate, an antithyroid agent inhibiting iodide trapping in the thyroid, was administered via the drinking water to half of the rats. Rats submitted to a normal laboratory diet and to the experimental diet supplemented with selenium were used as controls. The effects of selenium deficiency were an increase in the number of growth abnormalities, growth retardation, and decreased seleno-dependent glutathione peroxidase (GSH-Px) activity in plasma and in various organs. These effects were relieved by selenium supplementation in the diet. Perchlorate treatment induced the classic picture of primary hypothyroidism. Selenium deficiency increased thyroid hormone levels in perchlorate-treated rats and in controls drinking tap water. In the latter group, it also decreased TSH plasma concentration and thyroid weight. These effects were partially reversed by Se supplementation. In vitro experiments, performed on adult rats, revealed increased radioiodide uptake and organification in glands from the rats submitted to the selenium-free diet. Plasma T3 half-life was similar in control and Se-deficient rats. These data suggest a higher efficiency of thyroid hormone synthesis in the thyroids of selenium-deficient rats, despite a lower thyroid stimulation as evaluated by serum TSH. They are compatible with the hypothesis that decreased selenium supply, leading to a decreased GSH-Px in the thyroid, increases hydrogen peroxide steady state level and thus thyroid peroxidase activity and thyroid hormone synthesis.

The thyroid gland is a major source of circulating T3 in the rat.

“…Goldstein et al observed a decrease in PB 13"I after in vitro incubation of thyroid glands from selenium-deficient rats with 131I (27). Arthur et al (25) found a decrease in both T4 and T3 content in the thyroid gland from selenium-deficient rats, while Meinhold et al (28) found no change in T4 and T3 content in the thyroid from rats fed a selenium-deficient diet.…”

Selenium and the thyroid

“…Adequate Se intake increases the efficiency of thyroid hormone synthesis [39]. This has been shown in animal studies, but not fully explained with respect to underlying mechanisms.…”

Activities of UDP-glucuronyltransferase, beta-glucuronidase and deiodinase types I and II in hyper- and hypothyroid rats

“…To attain hypothyroidism, we employed an established protocol (van Hardeveld & Clausen 1984) in which rats were fed for 7 weeks an iodide-deficient diet with distilled water during the first 2 weeks and drinking water containing 144 mM KClO 4 for five consecutive weeks. This treatment has proven to result in the classic picture of hypothyroidism with decreased plasma T 4 and T 3 levels and rises in thyrotropin (TSH) (Golstein et al 1988, Yu et al 2002. Controls received the same diet, and drinking water to which 6·5 mg/l KI was added.…”