| Atrazine (ATZ) is a kind of herbicide for removing annual grasses and broad-leave weeds, now has become one of the most common pesticide pollutants in rivers, streams, and groundwater. ATZ has adverse impact on the growth and development of aquatic life, also can affect the gonad development and reproduction, the structure of testis, influence the formation of sperm and even cause its damage. Many studies focus on the endocrine disturbance of ATZ to mammals, amphibians and fish, but other studies have appeared opposite results, so for the question whether ATZ can interfere with the endocrine, and affect the growth of testis, there are more controversial.Testis development process is under the influence of steroidogenesis. ffld, StAR, P450play an important role in steroidogenesis. The expression of these genes affecting steroidogenesis and steroid levels make important influence on gonad development, the whole process is regulate by HPG axis. A large amount researches are on mammalian steroidogenesis and testis development, but the toxicity mechanism of ATZ is still unclear, and few studies of fish in this aspect.Adult zebrafish (Danio rerio) were exposed to ATZ(0,0.01,0.05,0.25,0.5,0.25,0.5mg/L) for21d. The expression of genes related to hormone synthesis in zebrafish testis were detected by fluorescence quantitative PCR(q-PCR), the concentration of E2and11-KT in testis was detected by ELISA and the tissue morphology of testis was investigated by routine histological section. Obtained following results:(1)0.01mg/L ATZ induced the expression of VTG mRNA, but others did not show any significant change, this induction effect showed out with no concentration effect relationship. And there were no significant induction of ERa.(2) ATZ down-regulated genes related to male hormones synthesis, high concentration ATZ decreased the androgen levels in testis. ATZ induced the synthesis of E2. In addition to O.Olmg/L, other treatments of ATZ could down-regulate androgen synthesis related genes (ffld, StAR, CYP17a1and CYP11b) significantly. Only high concentrations of ATZ could decrease the level of T and11-KT significantly; CYP19a1and E2was presented a kind of fluctuation increase (the expression of CYP19al were significantly increased in0.5mg/L, the level of E2was increased in0.01mg/L,0.25mg/L and2.0mg/L).(3)High concentration of ATZ can produce certain effect on the development of zebrafish testis. Also down-regulated the testis development related gene sox9a, resulted in slightly decline in the number of spermatogonia. And seminiferous tubule of testis structure showed the visible lesions, mainly caused small clearance between tubes. In addition to0.01mg/L, Dmrtl gene were significantly down-regulated in other treatments, but without observed visible lesions in testis tissue, may be the alteration on the level of transcription was still in the regulation range of HPG axis. Conclusion: ATZ can disturb endocrine system, induce estrogen effect, increase gene expression of VTG, and presents a kind of monotonous concentration effect relationship at low concentration. This induction may be not produced by nuclear receptor pathway, but through membrane receptor pathway. ATZ can down-regulate genes expression related to male steroidogenesis. And increase the level of E2, but only high concentration ATZ decrease the levels of T and11-KT, which results in the imbalance of sex hormone in testis. For lower treatment group, the levels of T and11-KT show no significant change, may be due to the negative feedback regulation of sex hormone imbalance of the HPG axis. ATZ down-regulate the expression of genes related to testis development, but ATZ can cause significant visible pathological changes of testis tissue at high concentration. Therefore we conclude that ATZ can cause sex hormone imbalance by affecting male hormone metabolism, which launched the negative feedback regulation of HPG axis. Also can down-regulate the expression of genes related to male steroidogenesis. But the action mechanism of ATZ still need further research. |
