In ovo exposure to atrazine alters thyroid histomorphology in late postnatal broad-snouted caiman (Caiman latirostris)

ALMADA, A.; TAVALIERI, Y.E.; LUQUE, E.H.; MUÑOZ DE TORO, M.; GALOPPO, G.H.

Buenos Aires

Congreso; XXIII Jornada Anual de la Sociedad Argentina de Biología; 2022

Sociedad Argentina de Biología

Previously, we demonstrated that prenatal exposure to environmentally relevant doses of the herbicide atrazine (ATZ) induce hypothyroid-like alterations in female Caiman latirostris thyroid gland, being the female caimans more sensitive to the exposure than males. However, if those alterations occur during juvenile stage of development or are the result of subtle changes that occur at earlier developmental stages remains unknown. Our objective was to assess if exposure to ATZ induces alterations in the thyroid gland of caimans at earlier developmental stages and to confirm sex-related effects due to the exposure. Eggs were incubated at female or male producing temperature (30°C or 33°C, respectively) and before sex determination takes place, they were exposed to 0.2 ppm of ATZ or ethanol (vehicle). When caimans reached the late postnatal stage (3 months), thyroid glands were excised and processed to paraffin embedding. Histomorphological studies (% of the gland occupied by stroma, epithelium, and colloid; follicular density; follicular area; follicular epithelial height; percentage of microfollicles and percentage of follicles showing grade 1, 2, or 3 of hyperplasia) and epithelial proliferative activity were performed on 5-μm thick tissue sections stained with PAS or immunomarked for proliferating cell nuclear antigen, respectively. Our results were expressed as mean ± SEM for vehicle vs. ATZ. In female caimans, ATZ exposure decreased follicular size (5902 ± 1301 vs. 2444 ± 260 μm2) and follicular epithelial height (11.31 ± 1.88 vs. 6.32 ± 0.36 μm) but increased the percentage of follicles showing hyperplasia grade 2 (4.33 ± 1.36 vs. 13.98 ± 2.65 %), the percentage of microfollicles (0.003 ± 0.003 vs. 0.075 ± 0.030), and the proliferative activity of the follicular epithelium (1.450 ± 0.661 vs. 2.985 ± 0.069 %). In males, ATZ exposure increased the proliferative activity of the follicular epithelium (1.202 ± 0.248 vs. 3.850 ± 0.483 %). The results regarding proliferative activity would explain the increased incidence of hyperplastic follicles (type 1 in males, types 2 and 3 in females) previously observed in juvenile caimans. On the other hand, these results confirm that female caimans are more sensitive to ATZ exposure than males and that the alterations in thyroid gland observed at juvenile stage begin at earlier developmental stages, suggesting that exposure to ATZ induce organizational effects that become evident as caimans grow and mature.