Exposure to perfluorooctane sulfonate based on circadian rhythm changes the fecundity and expression of certain genes on the hypothalamic-pituitary-gonadal-liver axis of female zebrafish

Exposure of a variety of experimental animals to perfluorooctane sulfonate (PFOS) has shown that it is a potent endocrine-disrupting chemical. However, its interaction with the circadian rhythm on responses along the hypothalamic – pituitary – gonadal – liver (HPGL) axis should be of significant value but has not been adequately investigated. In present study, the effects of PFOS on fecundity, levels of estradiol (E2) and expression of certain genes on the HPGL axis at two time points (8:00 AM and 7:00 PM) were compared after female zebrafish were exposed to 0, 2, 20 and 200 μg/L PFOS for 21 days. In brain, expressions of gonadotropin-releasing hormone (GnRH), gonadotropin-releasing hormone receptor (GnRHr), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were significantly different after the exposure when sampled at 8:00 AM and at 7:00 PM (P < .05). In liver, significant down-regulation of vitellogenin1 (VTG1) and estrogenic receptor α (ERα) were observed at 7:00 PM compared with 8:00 AM (P < .05). In ovary, the level of CYP19 was significantly different at the two time points (P < .05). The increase of E2 after exposure to 20 μg/L PFOS at 8:00 AM caused compensatory down-regulation of GnRHr and up-regulation of VTG1 and ERα, but not at 7:00 PM. Profiles of concentrations of E2 and several gene expressions alongside the HPGL axis were different between two times points. The change of E2 and gene expressions were more perturbed by PFOS at 8:00 AM than at 7:00 PM with circadian rhythm.