Modulation of vitellogenin synthesis through estrogen receptor beta-1 in goldfish (Carassius auratus) juveniles exposed to 17-β estradiol and nonylphenol

Many synthetic chemicals, termed xenoestrogens, have been shown to interact as agonists with the estrogen receptor (ER) to elicit biological responses similar to those of natural hormones. To date, the regulation of vitellogenesis in oviparous vertebrates has been widely used for evaluation of estrogenic effects. Therefore, Carassius auratus juveniles were chosen as a fish model for studying the effects of estradiol-17 beta and different concentrations (10(-6) and 10(-7) M) of 4-nonylphenol (4-NP) on the expression of liver ER beta-1 subtype; plasma vitellogenin and sex steroids (androgens and estradiol-17 beta) were also evaluated together with the bioaccumulation process, through mass-spectrometry. C. auratus is a species widespread in the aquatic environment and, on the toxicological point of view, can be considered a good "sentinel" species. Juveniles of goldfish were maintained in tanks with only tap water or water with different concentrations (10(-6) and 10(-7) M) of 4-nonylphenol (4-NP), or 10(-7) M of estradiol-17 beta. After 3 weeks of treatment, animals were anesthetized within 5 min after capture, and blood was immediately collected into heparinized syringes by cardiac puncture and stored at -70 degrees C; the gonads were fixed, then frozen and stored at -70 degrees C; the whole fish, liver, and muscle tissues were harvested and immediately stored at -70 degrees C for molecular biology experiments and bioaccumulation measurements. The estrogenic effects of 4-NP were evidenced by the presence of plasma vitellogenin in juveniles exposed both to estradiol-17 beta and the two doses of 4-NP; moreover, exposure to 4-NP also increased aromatization of androgens, as suggested by decreasing androgens and increasing estradiol-17 beta plasma levels. The changes of these parameters were in agreement with the increasing transcriptional rate of ER beta-1 mRNA in the liver, demonstrating that both estradiol-17 beta and 4-NP modulate the vitellogenin rate through interaction with the ER beta-1 subtype. The present study also suggests that 4-NP at the concentration of 10(-6) M bioaccumulates in the liver.