Endocrine Abstracts

The potential health threat posed by endocrine-disrupting chemicals has come to the forefront of environmental health in previous years and nowadays represents a major concern among scientific, regulatory and public communities. Different groups of environmental chemicals appear to have thyroid-disrupting properties. The lifelong exposure to these chemicals raises concerns about their deleterious effects on human health, having in mind that even subtle changes in the individual thyroid homeostasis during the life cycle may have significant adverse effects. This experimental study was aimed to assess effects of repeated relatively low doses (corresponding low to high environmental human exposures) of toxic metal cadmium (Cd), and persistent organic pollutants: polychlorinated biphenyls (PCBs), and polybrominated diphenyl ether (BDE 209) on thyroid homeostasis in adult animals. These chemicals were chosen based on their persistency, high toxicity and ubiquitous presence in environment. Rats were randomized into 20 experimental groups: 6 receiving aqueous solution of Cd (doses ranging from 0.3 to 10 mg/kg b.w.), 6 receiving PCBs dissolved in corn oil (0.5–16 mg/kg b.w.), 5 groups receiving BDE 209 dissolved in DMSO (31.25–500 mg/kg b.w.), and vehicle control groups. Treatment of all animals was performed by oral gavage, each day, during 28 days. Thyroid hormones were adversely affected by Cd, with most prominent effect observed on triiodothyroxine (T3) levels. Applied doses of PCBs induced dose dependent decrease in thyroxine levels (T4) while BDE 209 caused increase in T4 and decrease in T3 levels, compared to respective controls. The strong positive correlation between external/applied doses and target tissue content fortified the reliability of the obtained results. The study implicates that exposure to low, environmental doses of these chemicals interferes with thyroid function and raises an issue of their thyroid disruptive properties at levels to which human are exposed on daily bases.