Sammendrag
Regardless of steroidogenic organ or tissue, the StAR protein and P450scc are rapidly synthesized in response to acute tropic hormone stimulation. Early mammalian studies showed that the StAR protein is a 30-kDa protein that is first synthesized in the cytosol as 37-kDa precursor in response to the activation of cAMP protein kinase-A intracellular signaling pathways. Gonadal steroids are known to modulate both the synthesis and release of gonadotropins by the pituitary and influence several brain functions that are apparently responsible for gender-specific differences in the regulation of hypothalamus-pituitary-gonadal-liver (HPGL) axis. In the present study, we have studied the effects of nonylphenol (NP) on salmon previtellogenic oocytes using an in vitro culture system, molecular, histological and physiological methods. The in vitro culture technique was based on an agarose floating method recently validated in our laboratory for xenoestrogens. Tissue was cultured in a humidified incubator at 10 °C for 3, 7 and 14 d with different concentrations of NP (0 (control), 1, 10 and 50 mM) dissolved in ethanol (0.3%). The StAR, P450scc, P450arom isoforms and insulin-like growth factor 2 (IGF-2) mRNA expressions were performed using validated real-time polymerase chain reaction (PCR) with specific primers, immunohistochemistry of the StAR and P450scc proteins was performed using antisera prepared against synthetic peptide for both proteins and estradiol-17b (E2), testosterone (T) and 11-ketotestosterone (11-KT) tissue levels were performed using enzyme immunoassay. We show that NP produced effects on the StAR, P450scc, P450arom and IGF-2 gene expressions that were time- and concentration-specific responses. The StAR and P450scc proteins were mainly demonstrated in follicular cells of oocyte membrane, showing time- and NP concentration-dependent differences in staining intensities. Hormonal (E2, T and 11-KT) responses were modulated differently by NP, showing time- and concentration-specific effects. In general and consistent our previous studies in our laboratories using the brain and interrenal tissues, the present data suggest that NP modulates steroidogenesis by targeting the initial and rate-limiting step that involves the StAR protein. Thus showing that NP produces variations in key gonadal steroidogenic and growth regulating pathways. These effects and the hormonal imbalance reported in the present study may have potential consequences for the vitellogenic process and overt fecundity in teleosts.
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