Alterations In Testicular Histology And The MRNAs Of Enzymes Responsible For Sex Steroid Synthesis In The Zebrafish (Danio Rerio) Exposed To Nonyphenol And BisphenolA

The Endocrine disrupting chemicals (EDCs), interference with the synthesis of endocrine substances, release, transport, metabolism, and so the process of activation or inhibition of the function of the endocrine system and undermine the stability of internal environment, as a result they are capable of leading to reproductive problems, birth defects, developmental abnormalities, metabolic disorders and some cancers in the living body. Nonylphenol (NP) and Bisphenol A(BPA), aquatic endocrine disruptor, are known to be capable of adversely affecting fish development and reproduction. Many studies have shown that the testicular changes of animals, such as reduced sperm quality, decreased semen volume sperm unite, testis-ova, degradation of the testis fibrosis and so on are attributed to the contamination of EDCs. However, the studies on the molecular mechanisms for the harmful effects of NP and BPA on testicular development as well as its combination with testicular structure in fish are absent.Under natural conditions, hormones in fish regulate the development of testicular, by which 11-ketotestosterone (11-KT) and 17β-estradiol(E2) are the main synthesised hormone. Same with the other vertebrates, the synthesis and transformation of gonadal hormone in fish are regulated by the cytochrome P450 enzyme. P45011βhydroxylase (CYP11B)and P450 aromatase (CYP19A) are the key enzyme in the synthesis of 11-KT and E2. Therefore, the quantitative study of NP and BPA on the expression of gonadal cytochrome P450 enzymes, is an important way to elucidate the the mechanism of Endocrine disrupting chemicals (EDCs) on gonadal development in fish.In this paper, the pathway of NP and BPA on testicular sperm development and structure were investigated to provide the essential ecology toxicology data for biomarker screening and the environmental evaluation. However, this paper studied the joint effects of NP and BPA because of the complex field water environment and pollutants.In this paper, the adult male zebrafish were exposed to NP(0,125,250, 500μg·L-1), BPA(0,500,1000,2000,4000μg·L-1), the mixture of NP (62.5μg·L-1)and BPA(0,500,1000,2000μg·L-1) for 21 days. Histologically alterations in the testis and the mRNAs of enzymes responsible for sex steroid synthesis(CYP17, CYP11B, CYP19A), estrogen receptor a (ERa), androgen receptor (AR), Follicle-stimulating hormone receptor(FSHR) as well as the liver Vitellogenin(VTG) and estrogen receptor a (ERa) in were subsequently investigated.The results were summarized as follows:Histologically, With the increase of NP and BPA, the semen in seminiferous tubules decreased, mature sperm agglutination and the acellular zone enlarged. The fish treated with 1000μg·L-1 BPA have testis-ova. Degradation was observed in the highest concentration of NP and BPA. There was a typical of estrogenic effects and the expression of liver VTG and ERa were induced by the increasing concentration of NP and BPA, which induced the expression of CYP19A mRNA in testis. So VTG may be seemed as a biomarker of EDCs, the expression change of CYP19A and ERa mRNA may be as the early warning of EDCs. The NP and BPA markedly downregulated the expression of CYP17 gene in a concentration-response manner, however, the mixture of NP and BPA downregulate the CYP17. NP downregulate CYP11B gene, but NP+BPA upregulate CYP11B. So the mechanism ofNP and BPA maybe not exactly the same. BPA and the mixture of NP and BPA both upregulated the expression of FSHR. There was antagonism on the group of (NP62.5+BPA500)μg·L-1, but synergistic effect on the group of (NP62.5+BPA1000)μg·L-1 which was the most significant difference on expression of gene mRNA.Conclusion:(1) With the increased concentration of NP and BPA, there are less semen in the seminiferous tubules, more acellular zone, sperm agglutination and testis-ova. The results indicated that NP and BPA have comparatively obvious estrogenic effects. (2) NP and BPA may inhibit the testosterone (T) synthesis through down-regulating the expression of CYP17 and active the endogenous estrogen activity and promote its synthesis by up-regulating the expression of CYP19A. (3) NP down-regulate the expression of CYP11B and BPA have no effects on it. The results indicated that NP inhibit the synthesis of androgen, but do not interfere with its work, and BPA have no effects on its synthesis. (4) The mechanism ofNP and BPA, are not identical, but they both have destroyed the original balance of sex hormones. (5) There are both antagonistic action and synergistic action of the combined effects of NP and BPA, and NP disrupted the mechanism of BPA, which is very complicated.