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127 Monograph It has been shown that several xenobiotics in the environment are capable of inducing adverse effects in invertebrates and vertebrates, including humans, by interfering with the normal endocrine function of the organism (Colborn et al. 1993). Most studies have focused on endocrine disrupting chemicals (EDCs) that act as agonists at the(More)
Uncoupling proteins (UCPs) increase proton leakage across the inner mitochondrial membrane. Thereby, UCP1 in brown adipose tissue dissipates proton motive force as heat. This mechanism of nonshivering thermogenesis is considered as a monophyletic trait of endothermic placental mammals that emerged about 140 million years ago and provided a crucial advantage(More)
Although the invention and widespread use of artificial light is clearly one of the most important human technological advances, the transformation of nightscapes is increasingly recognized as having adverse effects. Night lighting may have serious physiological consequences for humans, ecological and evolutionary implications for animal and plant(More)
Debate and controversy exists concerning the potential for the herbicide atrazine to cause gonadal malformations in developing Xenopus laevis. Following review of the existing literature the U.S. Environmental Protection Agency required a rigorous investigation conducted under standardized procedures. X. laevis tadpoles were exposed to atrazine at(More)
In the present study, Xenopus laevis tadpoles were chronically exposed to four concentrations of the synthetic gestagen Levonorgestrel (LNG; 10(-11), 10(-10), 10(-9), and 10(-8)M) starting at Nieuwkoop and Faber (NF) stage 48 until completion of metamorphosis. At NF 58 and 66, brain-pituitary and gonad samples were taken for gene expression analyses of(More)
In Xenopus laevis the basic mechanisms underlying sexual differentiation were investigated by determining time courses of sexual steroids and their corresponding receptors during complete larval development from egg to juveniles. Androgens as well as estradiol (E2) are derived from maternal origin and accumulate in hatching tadpoles. Sexual steroid contents(More)
Amphibian metamorphosis represents a promising model for the identification of thyroid system-disrupting chemicals due to the pivotal role played by thyroid hormones for the initiation and regulation of metamorphosis. An important aspect of bioassay development is the identification and evaluation of sensitive and diagnostic endpoints. In this study,(More)
Xenopus laevis has been introduced as a model to study effects of endocrine-active compounds (EAC) on development and sexual differentiation. However, variable and inconsistent data have raised questions about the reliability of the test methods applied. The current study was conducted in two laboratories to develop, refine, and standardize procedures and(More)
Vinclozolin (VIN) is an antiandrogenic model substance as well as a common fungicide that can affect the endocrine system of vertebrates. The objective of this study was to investigate how VIN affects mate calling behavior of South African clawed frogs (Xenopus laevis) and whether it is effective at environmentally relevant concentrations. Male X. laevis(More)