Endocrine Abstracts

Toxic metals can disrupt the endocrine system, harming the thyroid and male reproductive function, as indicated by epidemiological and experimental studies. A human biomonitoring study in Serbia determined the levels of toxic metals (Cd, Pb, As, Hg, Cr, and Ni) in the blood to identify real life scenario of exposure. On the basis of the metal measured levels, the doses for the oral 90 days treatment of male Wistar rats were calculated. The experiment included a control group and treatment groups that received doses reflecting the lower confidence limit of the Benchmark dose for effects on hormone levels (M1), median concentrations (M2) and 95th percentiles concentration of each metal (M3). Serum levels of the hormones TSH, fT4, fT3, T4, T3, testosterone, FSH and LH were determined. A histological analysis of the thyroid gland tissue was performed, while the redox status parameters (IMA, MDA, SH groups, GSH and SOD) were determined in the testicular tissue. Additionally, SPINA-GT and SPINA-GD were calculated with the SPINA Thyr software. In group M2 there was a statistically significant decrease in TSH levels and an increase in fT4 levels, while in group M3 a decrease in fT3 levels was observed. The levels of T4 and T3 remained relatively stable in all groups, although a decreasing trend of T3 in M3 and an increasing trend of T4 in M2 were observed. A significant decrease in SPINA-GD in all treated groups indicates a decreased activity of peripheral deiodinases, while the secretory activity of the gland was not significantly changed in any of the treated groups. Histological analysis of the thyroid tissue showed changes in all treated groups, despite the fact that in some of the treated groups no changes were observed in the levels of TSH and thyroid hormones, which can be explained by the activation of compensatory mechanisms. The analysis of reproductive hormones in the serum showed that only in the group that was exposed to the highest doses of the tested metals (M3), there was a significant decrease in the level of LH. In the M1 group, group treated with the lowest doses of metals, a decrease in the levels SH groups, GSH, and SOD was observed. This outcome may be a consequence of depletion of antioxidant protection reserves. It can be concluded that environmentally relevant doses of metals mixtures can affect the function and structure of the thyroid gland and the male reproductive system.