Department of Ecophysiology and Aquaculture, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, D-12587 Berlin, Germany.
Gen Comp Endocrinol. 2010 Sep 1;168(2):245-55. doi: 10.1016/j.ygcen.2010.03.005. Epub 2010 Mar 11.
The occurrence of natural substances acting as endocrine disrupting compounds (EDC) in the environment is to date poorly understood. Therefore, (anti)androgenic and (anti)estrogenic activities of three different aqueous leaf extracts (beech, reed and oak) were analyzed in vitro using yeast androgen and estrogen screen. The most potent extract was selected for in vivo exposure of Xenopus laevis tadpoles to analyze the potential effects on development and reproductive biology of amphibians. Tadpoles were exposed from stage 48 to stage 66 (end of metamorphosis) to aqueous oak leaf extracts covering natural occurring environmental concentrations of dissolved organic carbon. Gene expression analyses of selected genes of the hypothalamus-pituitary-gonad and of the hypothalamus-pituitary-thyroid axis as well as histological investigation of gonads and thyroid glands were used to evaluate endocrine disrupting effects on the reproductive biology and development. Female tadpoles remained unaffected by the exposure whereas males showed severe significant histological alterations of testes at the two highest oak leaf extract concentrations demonstrated by the occurrence of lacunae and oogonia. In addition, a significant elevation of luteinizing hormone beta mRNA expression with increasing extract concentration in male tadpoles indicates an involvement of hypothalamus-pituitary-gonad axis mainly via antiandrogenic activity. These results suggest that antiandrogenic EDC of oak leaf extract are responsible for inducing the observed effects in male tadpoles. The present study demonstrates for the first time that in surface waters, natural occurring oak leaf compounds at environmentally relevant concentrations display antiandrogenic activities and have considerable effects on the endocrine system of anurans affecting sexual differentiation of male tadpoles.
目前，人们对环境中天然物质作为内分泌干扰化合物 (EDC) 的出现知之甚少。因此，本研究使用酵母雄激素和雌激素筛选法，体外分析了三种不同的水提叶片提取物（山毛榉、芦苇和橡树）的抗雄激素和抗雌激素活性。选择活性最强的提取物，对非洲爪蟾蝌蚪进行体内暴露实验，以分析其对两栖动物发育和生殖生物学的潜在影响。从第 48 期到第 66 期（变态期末），将蝌蚪暴露于水提橡树叶片提取物中，提取物中包含天然存在的溶解有机碳环境浓度。选择下丘脑-垂体-性腺和下丘脑-垂体-甲状腺轴的特定基因进行基因表达分析，以及对性腺和甲状腺进行组织学研究，用于评估对生殖生物学和发育的内分泌干扰作用。暴露对雌性蝌蚪没有影响，而雄性蝌蚪在最高的两个橡树叶片提取物浓度下，睾丸出现严重的组织学改变，表现为腔隙和卵母细胞的出现。此外，随着提取物浓度的增加，雄性蝌蚪中黄体生成素β mRNA 表达的显著升高表明，下丘脑-垂体-性腺轴主要通过抗雄激素活性参与其中。这些结果表明，橡树叶片提取物中的抗雄激素 EDC 是导致雄性蝌蚪观察到的影响的原因。本研究首次证明，在地表水中，天然存在的橡树化合物在环境相关浓度下表现出抗雄激素活性，并对无尾目动物的内分泌系统产生相当大的影响，从而影响雄性蝌蚪的性分化。
