title: Environmental signals: synthetic humic substances act as xeno-estrogen and affect the thyroid system of Xenopus laevis.
abstract: According to outdated paradigms humic substances (HS) are considered to be refractory or inert that do not directly interact with aquatic organisms. However, they are taken up and induce biotransformation activities and may act as hormone-like substances. In the present study, we tested whether HS can interfere with endocrine regulation in the amphibian Xenopus laevis. In order to exclude contamination with phyto-hormones, which may occur in environmental isolates, the artificial HS1500 was applied. The in vivo results showed that HS1500 causes significant estrogenic effects on X. laevis during its larval development and results of semi-quantitative RT-PCR revealed a marked increase of the estrogenic biomarker estrogen receptor mRNA (ER-mRNA). Furthermore, preliminary RT-PCR results showed that the thyroid-stimulating hormone (TSHbeta-mRNA) is enhanced after exposure to HS1500, indicating a weak adverse effect on T3/T4 availability. Hence, HS may have estrogenic and anti-thyroidal effects on aquatic animals, and therefore may influence the structure of aquatic communities and they may be considered environmental signaling chemicals.
authors.affiliation: Leibniz-Institute of Freshwater, Ecology and Inland Fisheries, Müggelseedamm 310, D-12587 Berlin, Germany.
authors.forename: Ilka
authors.initials: I
authors.lastname: Lutz
authors.forename: Zhang
authors.initials: Z
authors.lastname: Jie
authors.forename: Robert
authors.initials: R
authors.lastname: Opitz
authors.forename: Werner
authors.initials: W
authors.lastname: Kloas
authors.forename: Xu
authors.initials: X
authors.lastname: Ying
authors.forename: Ralph
authors.initials: R
authors.lastname: Menzel
authors.forename: Christian E W
authors.initials: CE
authors.lastname: Steinberg
mesh_terms: D000818:Animals; D004967:Estrogens / Q000633:toxicity*; D005260:Female; D006812:Humic Substances; D007814:Larva / Q000254:growth & development / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D012333:RNA, Messenger / Q000378:metabolism; D011960:Receptors, Estrogen / Q000096:biosynthesis* / Q000235:genetics; D012098:Reproduction / Q000187:drug effects; D012744:Sex Ratio; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism; D037322:Thyrotropin, beta Subunit / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis / Q000254:growth & development / Q000378:metabolism*
chemical_list: D004967:Estrogens; D006812:Humic Substances; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D037322:Thyrotropin, beta Subunit