Thyroid Hormones as Potential Early Biomarkers of Exposure to Nonylphenol in Adult Male Lizard (Podarcis sicula)

The thyroid has been shown to be a target organ of environmental chemicals, specifically endocrine disrupting contaminants. Reptiles are particularly suitable as contaminant biomonitors, due to their persistence in a variety of habitats, wide geographic distribution, longevity, and, in many cases, site fidelity. Nonylphenol, an estrogenic-like compound, can induce vitellogenin synthesis in males and immature reptilian species, but little is known about its effects on thyroid hormones balance. The present study evaluated the potential effects of an acute exposure to nonylphenol (i.p. injected) on the thyroid of the lizard Podarcis sicula. Nonylphenol induced a significant decrease of T4 and T3 plasma levels, in agreement with the decrease of the epithelial cell height; the nuclei of the thyroid cells were small and elongated, with dense chromatin and a greatly reduced cytoplasm. The colloid was retracted with few reabsorption vacuoles. Moreover, nonylphenol administration significantly inhibited plasma thyroid-stimulating hormone levels, thereby altering the thyroid function. This study highlights how the structural and functional disruption of the thyroid gland in non-target organisms as the lizard might also have an environmental aetiology. In conclusion, nonylphenol was suspected to inhibit the thyroid hormones balance, suggesting the thyroid should be included among the other endocrine glands, susceptible to endocrine