Endocrine Abstracts

Environmental compounds can interfere with endocrine systems of wildlife and humans. The main sink of such substances, called endocrine disruptors (ED), are surface waters; and thus aquatic vertebrates such as fishes and amphibians are most endangered. Despite numerous reports on ED in fishes exist, information about ED in amphibians is relatively scarce but emerging. Amphibians can be affected sensitively by ED via adverse effects on reproductive biology and development e.g. metamorphosis triggered by the thyroid system. In amphibians, ED can affect reproductive biology by (anti)estrogenic and (anti)androgenic modes of action resulting in severe endocrine effects including abnormal sexual differentiation. These effects are mainly driven by direct interferences of ED with sex steroid receptors or indirectly by impacting synthesis and bioavailability of sex steroids. Recent development of flow-through exposure systems indicate that larval exposure of amphibians results in a similar sensitivity concerning impacts on sexual differentiation compared to established fish models. ED actions on thyroid system cause acceleration or retardation of metamorphosis mainly via changes in bioavailability of thyroid hormones rather than by direct interferences with thyroid hormone receptors. Our broad knowledge of amphibian biology and endocrinology indicates that amphibians are very suitable sensors for the study of ED. In particular, the effects of ED on the thyroid system triggering metamorphosis can be determined easily and most sensitively in amphibians compared to other vertebrates including mammals. Methods and strategies are proposed for tracking and risk assessment of ED using amphibians as model. Recently, the emerging ecotoxicological issue of pharmaceuticals present in the environment indicates a high potential of further modes of action disrupting endocrine system of amphibians for instance by glucocorticoids and progestogins.