Luteinizing hormone, follicle stimulating hormone, and gonadotropin releasing hormone mRNA expression of Xenopus laevis in response to endocrine disrupting compounds affecting reproductive biology

Abstract

Environmental pollutants can interfere with the endocrine system of a variety of animals and are suggested to contribute to the worldwide decline of amphibians. In this study, the effects of endocrine disrupting compounds (EDC) on the hypothalamus–pituitary–gonad axis, regulating reproduction, were investigated in Xenopus laevis by determining their potential impact on gene expression of gonadotropin releasing hormone (GnRH), luteinizing hormone β-subunit (LHβ) and follicle-stimulating hormone β-subunit (FSHβ) in brain and pituitary using semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). One environmental sample and four model compounds, ethinylestradiol (EE2), tamoxifen (TAM), methyldihydrotestosterone (MDHT), and flutamide (FLU), corresponding to (anti)estrogenic and (anti)androgenic modes of action were used at 10 −8 M during a four weeks exposure of adults of both sexes. In general, males had a higher LHβ mRNA level compared to females, while the mRNA expression of FSHβ and GnRH did not differ between both sexes. EE2 and MDHT treatment decreased LHβ mRNA expression in the brain of male X. laevis, while only EE2 but not MDHT reduced LHβ mRNA in females indicating classical negative feed-back mechanisms on hypophyseal gonadotropin expression. TAM increased LHβ mRNA and FSHβ mRNA expression in female X. laevis while none of the other treatments showed an effect on FSHβ mRNA expression. GnRH expression was not changed by any treatment and exposure of X. laevis to Lambro river water had no significant effect on any of the genes examined. It is reported for the first time in amphibians that gonadotropin mRNA expression is differentially regulated by (anti)estrogenic and (anti)androgenic EDC and that gender-specific patterns of gene expression exist.