CONICET | Buscador de Institutos y Recursos Humanos

Thyroid hormones (triiodothyronine, T3 and thyroxine, T4) play an important role on development, growth and reproduction in vertebrate species. Evidences suggest that prenatal/early post-natal exposure of wildlife to endocrine disruptor compounds (EDC) affect thyroid function having consequences later in life. Caiman latirostris is highly sensitive to endocrine disruption. Endosulfan is an environmentally ubiquitous pesticide classified as EDC that behave as xenoestrogen. Endosulfan was detected in Caiman latirostris eggs, collected in areas with high anthropogenic intervention, demonstrating natural prenatal exposure. Preliminary results from our lab showed that juvenile Caiman latirostris exposed in ovo to Endosulfan exhibit a trend to decreased levels of T4. The aim of this study was to characterize thyroid histo-functional biomarkers in juvenile male and female caimans and to assess the effect of prenatal exposure to Endosulfan on thyroid histo-architecture and histo-functionality. Eggs from low anthropogenic intervention areas were exposed to Endosulfan or vehicle (ethanol) prior to temperature sex determination. Vehicle treated eggs were equally distributed and incubated at male or female producing temperature. Eggs exposed to 20ppm of Endosulfan (environmentally relevant dose) were incubated at female-producing temperature. Hatchlings were raised under controlled conditions until juvenile stage. Upon sacrifice, thyroid glands were dissected, formaldehyde-fixed and processed until paraffin embedded. Using histological sections stained with PAS, histo-functional parameters such as: follicle density, follicular size distribution, percentage of the thyroid occupied by stroma, epithelium, or follicular colloid were assessed. Follicular size was categorized into three groups, small, medium and large follicles. Estrogen receptor-alpha (ERα) expression was revealed by immunohistochemistry and expressed as percentage of positive cell. All histo-functional parameter exhibited no differences between juvenile males and females but percentage of large follicles that was higher in females. Follicular epithelia expressed ERα, suggesting that it could be a target of xenoestrogens such as Endosulfan. Thyroid glands from Endosulfan treated female animals showed a decreased area of follicular colloid. Moreover, increased ERα epithelial expression, as reported in rat uterus and mammary gland after Endosulfan treatment, was observed. Previous results regarding T4 levels and these new findings suggest that Endosulfan interferes with thyroid hormones synthesis, and colloid depletion could be the response mechanism for maintaining circulating thyroid hormones level. As far as we know, this is the first time that Caiman latirostris thyroid gland histofunctionality is described. Additionally, this study alerts about the effects of Endosulfan environmental pollution on Caiman latirostris thyroid homeostasis.