| Environmental endocrine disrupting chemicals(EDCs),also known as environmental hormones,refer to the chemicals presented in the environment which can interfere with nerves,immune systems and normal function of endocrine regulation.With the increasing deterioration of aquatic ecosystems,the toxicological effects of EDCs on aquatic organisms have become a hot research area in ecotoxicology.Bisphenol AF has endocrine disrupting effects on organisms.To study the effects of BPAF on organism in aquatic ecosystems,adult zebrafish(Danio rerio)were exposed to 0.005,0.05 and 0.5 mg ·L-1 BPAF for 30 days.The possible mechanisms of disrupting effects of BPAF can be assessed by three main aspects which include the histopathologic lesions,the hypothalamic-pituitary-gonad axis and the level of thyroid hormones.The results of toxicity test on adult zebrafish showed that the changes of gonad's tissue lesions can be observed due to the exposure of BPAF.BPAF significantly inhibited female zebrafish ovary development.The decreasing number of sperm counts and increasing non-testis cell areas were induced by BPAF.The effects of BPAF on hypothalamns-pituitary-gonad(HPG)axis of adult zebrafish were evaluated.The levels of plasma vitellogenin(VTG)and the contents of homogenate sex steroids of zebrafish were examined by ELISA.The expression of two kinds of vtg mRNA(vtg-1 and vtg-3)and two kinds of aromatase genes(cypl9a and cypl9b)were also analyzed after BPAF exposure by realtime fluorescence quantitative PCR.Our result showed that the HPG axis of zebrafish was affected by BPAF:(1)a significantly high level of VTG could be induced by 0.005mg·L-1 BPAF for 30 days' exposure,but no significant upgrade of VTG was observed with the exposure to higher level of BPAF.(2)Multiple effects were displayed by BPAF on four kinds of genes expression in different tissues.While treated with 0.5 mg·L-1 BPAF,the expressions of vtg-1 and vtg-3 mRNA in the brains and cypl9a mRNA in the gonads were significantly increased.In a conclusion,BPAF can cause the increase of VTG content in the plasma of zebrafish,thereby interfering with the physiological processes of hypothalamus-pituitary-gonad axisWhen exposed to 0.5 mg·L-1 BPAF,in the thyroid,severe hyperplasia together with an increase in follicle number could be detected.And colloid showed alterations and the tinctorial properties and the texture of the colloid changed dramatically.The effects of BPAF on thyroid hormones of adult zebrafish were also evaluated.The levels of homogenate thyroid hormones(TT3,TT4,FT3 and FT4)of zebrafish were examined by ELISA.In order to assess the potential mechanisms of thyroid hormones' disruption of BPAF,the expressions of 2 kinds of related genes were determined.Our result showed that:(1)After 30 days' exposure of BPAF,the contents of TT3,FT3 and FT4 in zebrafish body homogenates were reduced by 0.005 mg·L-1 BPAF,while the content of TT4 was significantly induced by 0.5 mg·L-1 BPAF.(2)Different concentrations of BPAF have different effects on expression of genes in different tissues.With 0.005 mg·L-1 BPAF,the expressions of thyroid stimulating hormone(tsh)and deiodinase 2(dio2)were down-regulated in female zebrafish.The expression of the female zebrafish's tsh and dio2 mRNA were gradually increased with increasing dose of BPAF.In contrast,the expressions of tsh and dio2 mRNA were significantly induced by 0.005 mg·L-1 BPAF,however,the expression level of tsh mRNA was gradually decreased and accompanied by a significant increase in dio2 mRNA expression with the dose increased.The results showed BPAF had some thyroxine-disrupting effects on adult zebrafish. |
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