Aluminium effects on thyroid gland function: iodide uptake, hormone biosynthesis and secretion

The effects of aluminium (Al) on thyroid function were evaluated in adult Wistar rats intraperitoneally (i.p) injected with 7 mg Al (as lactate)/kg body weight (b.w) per day during a six week period. The time-course kinetics of Na¹²⁵I (3 μCi per 100 g b.w, i.p) was analysed by measuring gamma-radioactivity of thyroid, serum, serum protein precipitate and bile, at times ranging from 2 to 96 h post-dosing. In Al-treated group the ¹²⁵I⁻ thyroid uptake at 24 h (15,840 ± 570 vs. 18,030 ± 630 dpm/mg, P < 0.05) as well as the rate of ¹²⁵I⁻ release from the gland, calculated as the slope of the plot between 24 and 96 h (84 ± 8 vs. 129 ± 11 dpm/mg/h, P < 0.05) were significantly reduced as compared to control. The biliary ¹²⁵I⁻ excretion was not modified at all studied times. The Al content and lipid peroxidation (69.1 ± 8.5 vs. 53.2 ± 7.0 nmol MDA/g wet weight, P < 0.05) of thyroid tissue were increased in Al-treated rats. The serum concentrations of total thyroxine (T4, 3.78 ± 0.14 vs. 4.68 ± 0.12 μg/dL, P < 0.05) and total triiodothyronine (T3, 47 ± 4 vs. 66 ± 5 ng/dL, P < 0.05) were decreased by effect of Al, but free-T4 (1.05 ± 0.05 vs. 1.04 ± 0.04 ng/dL, NS) and thyrotropin (TSH, 2.7 ± 0.4 vs. 2.6 ± 0.5 ng/ml, NS) remain unchanged. In spite of the Al could indirectly affect thyroid iodide uptake and hormones secretion by a mechanism involving the induction of an oxidative stress state, however, these changes could be managed by the hypothalamus-pituitary-thyroid endocrine axis. We can conclude that in adult rats the Al would not act as a thyroid disruptor.