Modulation of salmon ovarian steroidogenesis and growth factor responses by the xenoestrogen, 4-nonylphenol

Abstract

Endocrine-disrupting chemicals are known to influence organismal reproductive processes, including the production and regulation of gonadal steroids. This study evaluated the effects of a xenoestrogen (nonylphenol: NP) on salmon ovarian steroidogenesis and growth factors using an in vitro organ culture system. Ovarian tissues were cultivated for 3 and 7 d with different concentrations of NP (0 (control), 1, 10 and 50 μM) dissolved in ethanol (0.1%). The mRNA expressions of steroidogenic acute regulatory (StAR) protein, P450-mediated cholesterol side-chain cleavage (P450 scc), aromatase isoforms, 3β-hydroxysteroid dehydrogenase (3β-HSD), Cyp11β-, Cyp17 and 21-hydroxylase, and insulin-like growth factors (IGF-1 and IGF-2) and IGF1-receptor (IGF1-R) were quantified by real-time PCR. Tissue levels of estradiol-17β (E2), testosterone (T) and 11-ketotestosterone (11-KT) were quantified using enzyme immunoassays. Our data show that nominal NP levels produced time- and concentration-specific effects on the expression of steroidogenesis- and IGF-related transcripts in salmon ovarian tissues. Tissue levels of ovarian E2, T and 11-KT were significantly modulated after NP exposure. Interestingly, elevated ovarian E2 levels after 10 μM NP exposure at day 3 paralleled P450 Arom isoforms mRNA expression at the same time interval. The expression patterns of other steroidogenic protein and enzyme genes, such as StAR, P450 scc, 3β-HSD and Cyp17 inversely paralleled this pattern, displaying consistent decreased transcript levels. These findings show that NP (an ubiquitous environmental pollutant) can produce variations in gonadal steroidogenesis and growth regulating responses with potential consequences for overt fecundity in teleosts.