Dynamics of estrogen biomarker responses in rainbow trout exposed to 17β‐estradiol and 17α‐ethinylestradiol

<jats:title>Abstract</jats:title><jats:p>We have investigated the response dynamics of the estrogen‐dependent genes vitellogenin (VTG) and the vitelline envelope proteins (VEPs) as well as circulating VTG in immature female rainbow trout (<jats:italic>Oncorhynchus mykiss</jats:italic>) exposed to 17β‐estradiol (E<jats:sub>2</jats:sub>) and 17α‐efhinylestradiol (EE<jats:sub>2</jats:sub>) for periods of 7 and 14 d. Gene responses were quantified by measurement of messenger RNA (mRNA) in liver extracts using a chemiluminescent hybridization protection assay. Circulating VTG was measured by a homologous enzyme‐linked immunosorbent assay. Exposure to both E<jats:sub>2</jats:sub> and EE<jats:sub>2</jats:sub> induced concentration‐dependent increases in all biomarkers. The data presented indicate that VEP genes may be more sensitive to estrogens than the VTG gene. The biomarker lowest‐observed‐effect concentrations (<jats:sup>biomarker</jats:sup>LOEC) in the 14‐d study with E<jats:sub>2</jats:sub> were 14 ng/L (VTG protein, VTG mRNA, VEPβ, and VEPγ) or 4.8 ng/L (VEPα). The EE<jats:sub>2</jats:sub> was 5‐ to 66‐fold more potent depending on the biomarker studied. In the 7‐d study, all biomarkers were elevated after 48‐h exposure to E<jats:sub>2</jats:sub>, with <jats:sup>biomarker</jats:sup>LOECs of 30 ng/L (VTG protein, VTG mRNA, and VEPγ) or 9.7 ng/L (VEPα and VEPβ). Vitellogenin mRNA was induced up to 1,000‐fold above baseline, and this translated into an increase of approximately 50,000‐fold in circulating VTG. In conclusion, all biomarkers responded to estrogen exposure at environmentally relevant concentrations.</jats:p>