Neuropeptide Y (NPY) is a small signalling molecule produced by neurons through the cleavage of a precursor protein. It generally binds to and activates G protein-coupled receptors to modulate complex homeostatic processes and behaviours in animals. Mammals provide definitive proof of the role of NPY in the thyroid axis, but in reptiles, this link is unclear. We demonstrate that the thyroid axis responds to NPY administration in a dose-dependent manner, with a reduction in plasma TRH and TSH concentrations, and an increase in plasma T₃ and T₄ levels 2 and 24 h after administration, suggesting that NPY may activate the thyroid axis. This increase in thyroid hormones is supported by morphological findings in the thyroid gland, which show clear signs of stimulation demonstrated by a dose-dependent increase in the height of the follicular epithelium and the presence of numerous resorption vacuoles. Moreover, we investigated the 5-T₄ ORD (type II) Monodeiodinase activity at the hepatic level, showing that NPY increased hepatic T₃ levels and decreased hepatic T₄ levels, and suggesting an alternative mode of signalling by NPY on peripheral biosynthesis of thyroid hormones. Our study helps to address the current lack of research in the field of endocrinology concerning the effects of NPY on metabolism and thyroid function.

Nonylphenol (NP) is a chemical compound belonging to the class of alkylphenols (APs), known for its widespread environmental distribution and endocrine-disrupting properties. It is commonly used in the production of detergents, pesticides, and plastic materials and, owing to these properties, it can accumulate in both aquatic and terrestrial ecosystems. As a xenoestrogenic compound, NP can bind steroid receptors, including estrogen receptors (ERs), thereby activating ER-dependent pathways. In this work, we investigated the effects of NP alone and in combination with the endogenous hormones 17β-oestradiol (E2) and/or testosterone (T) on a human non-tumoral prostate cell line (PNT1A). Cell viability and migration assays, together with analysis of ER expression and localization, were carried out to assess the xenoestrogenic activity of NP, particularly in the presence of E2 and T. Our results showed that NP retained its endocrine-disrupting features in the mixtures, positively affecting cell viability, except for the NP+E2 mixture, in which cell viability did not significantly differ from control, suggesting an antagonistic interaction between NP and E2. The mixtures also interfered with steroid receptor dynamics, affecting receptor expression and delaying receptor localization and activation kinetics. Moreover, all mixtures negatively affected cell migration compared with treatment with endogenous hormones alone. In conclusion, our results demonstrate that NP retains its xenoestrogenic behavior in mixture, inducing a significant alteration in prostate cell homeostasis.