MODULATION OF STEROIDOGENIC GENES, PROTEINS AND ACTIVITY LEVELS IN MULTIPLE ORGANS OF ATLANTIC SALMON BY NONYLPHENOL AND EHTYNYLESTRADIOL

The cytochrome P450 aromatase (P450arom) catalyzes the rate-limiting step in estrogen production and is the main regulator of local and systemic estrogen levels in the body. Teleost fish have a high brain aromatase activity, and the effects of EDCs in fish brain are not thoroughly investigated. In this study, juvenile Atlantic salmon were exposed to waterborne concentrations of ethynylestradiol (EE2; 5 ng/l) and nonylphenol (NP; 5 and 50 μg/l) for 72 hours. Tissue and blood were sampled from individual fish (n=5). Gene expression patterns of aromatase isoforms, steroid acute regulatory (StAR) protein, CYP11β, CYP21 and estrogen receptor (ERα) were determined by qPCR. Aromatase protein immunoreactivity in the brain was evaluated by immunohistochemistry. Aromatase activity was analyzed using the tritated water-release assay. Tissue aromatase protein levels were measured by ELISA, and plasma estradiol (E2) and testosterone (T) levels were measured by EIA. In the brain, EE2 increased P450aromB mRNA expression almost 3- fold compared to solvent control, whereas P450aromA levels were unaffected by EE2 treatment. In contrast, NP concentrations produced significant reduction of brain P450aromA expression. No significant effects of the exposures were observed for aromatase protein levels. However, plasma E2 levels increased 2-fold with EE2 and 5 μg/L NP, and 3-fold after 50 μg/L NP exposure. This study shows that endocrine disrupting effects of EE2 and NP may be observed at specific levels of biological organization. Whereas aromatase transcriptional levels and E2 plasma levels were modulated by EE2 and NP, no effects of the treatments were observed in aromatase protein levels.