Abstract
Since it is known that environmental contaminants have the potential to cause endocrine disorders in humans and animals, there is an urgent need for in vivo tests to assess possible effects of these endocrine disrupting chemicals (EDCs). Although there is no standardized guideline, the avian embryo has proven to be particularly promising as it responds sensitively to a number of EDCs preferentially impacting the reproductive axis. In the present study we examined the effects of in ovo exposure to fulvestrant and tamoxifen as antiestrogenic model compounds and co-exposure to both substances and the potent estrogen 17α-ethinylestradiol (EE2) regarding sex differentiation and embryonic development of the domestic fowl (Gallus gallus domesticus). The substances were injected into the yolk of fertilized eggs on embryonic day 1. On embryonic day 19 sex genotype and phenotype were determined, followed by gross morphological and histological examination of the gonads. Sole EE2-treatment (20 ng/g egg) particularly affected male gonads and resulted in an increased formation of female-like gonadal cortex tissue and a reduction of seminiferous tubules. In ovo exposure to tamoxifen (0.1/1/10 µg/g egg) strongly impaired the differentiation of female gonads, led to a significant size reduction of the left ovary and induced malformations of the ovarian cortex, while fulvestrant (0.1/1/10 µg/g egg) did not affect sexual differentiation. However, both antiestrogens were able to antagonize the feminizing effects of EE2in genetic males when administered simultaneously. Since both estrogens and antiestrogens induce concentration-dependent morphological alterations of the sex organs, the chick embryo can be regarded as a promising model for the identification of chemicals with estrogenic and antiestrogenic activity.
Highlights
In recent decades, reproductive disorders in animals and humans and the potential role of chemical substances that are suspected to cause these effects through their endocrine potential became of great interest for science and society
In ovo exposure to tamoxifen (0.1/1/10 μg/g egg) strongly impaired the differentiation of female gonads, led to a significant size reduction of the left ovary and induced malformations of the ovarian cortex, while fulvestrant (0.1/1/10 μg/g egg) did not affect sexual differentiation. Both antiestrogens were able to antagonize the feminizing effects of EE2 in genetic males when administered simultaneously. Since both estrogens and antiestrogens induce concentration-dependent morphological alterations of the sex organs, the chick embryo can be regarded as a promising model for the identification of chemicals with estrogenic and antiestrogenic activity
If a chemical substance has the same effects as endogenous sex hormones at the estrogen or androgen receptor, this substance acts as an agonist and its effects are referred to as estrogenic or androgenic
Summary
Reproductive disorders in animals and humans and the potential role of chemical substances that are suspected to cause these effects through their endocrine potential became of great interest for science and society. In the study of steroidal and non-steroidal substances, e.g., bisphenol A (BPA), 17α-ethinylestradiol (EE2), tributyltin (TBT) and many more, hormonal effects on different groups of organisms have already been identified (Peakall & Lincer, 1996; Berg et al, 1998; Berg et al, 1999; Watts, Pascoe & Carroll, 2001; Grote et al, 2004; Berg & Pettersson, 2006; Oehlmann et al, 2006; Pettersson et al, 2006; Ahn et al, 2007; Choi et al, 2007; Bodiguel et al, 2009; Scheider et al, 2018; Jessl, Scheider & Oehlmann, 2018) These studies underline the assumption that numerous chemicals have an endocrine potential and may pose a potential threat to the ecosystem and to animal and human health
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