Environmentally relevant polycyclic aromatic hydrocarbon mixtures disrupt ovarian endocrine function in the domestic hen (Gallus gallus domesticus).

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants known for their ability to bioaccumulate and disrupt biological processes, including reproductive functions. While the effects of individual PAHs, such as benzo[a]pyrene, on ovarian steroidogenesis have been studied in aquatic species, the impact of PAH mixtures remains poorly understood, particularly in birds. This study investigated the effects of a mixture of 16 priority PAHs, at concentrations reflecting those found in chicken egg yolk, on the production of steroid hormones and related molecular pathways in the ovary of the domestic hen (Gallus gallus domesticus). Hens were exposed to two PAH mixtures (MIX I and MIX II representing concentrations in free-range and caged hens, respectively) for 7 and 28 days. Plasma concentrations of progesterone (P4), testosterone (T), estradiol (E2), and luteinising hormone were measured, while gene expression and protein levels of key steroidogenic enzymes and receptors in ovarian follicles were analysed. Short-term exposure to both mixtures did not significantly affect hormone levels or gene expression, although reductions in receptor proteins were observed. In contrast, prolonged exposure induced a significant, mixture-specific endocrine disruption. MIX I reduced P4 concentration and increased the T/P4 ratio, whereas MIX II decreased T and increased E2 concentrations, resulting in an elevated E2/T ratio. At the molecular level, MIX II altered steroidogenic gene expression. However, protein levels of enzymes and receptors were generally reduced after 28 days. In conclusion, PAH mixtures disrupt ovarian function in a time- and mixture-dependent manner, highlighting potential reproductive risks in birds.