Effects of p,p'-DDE on retinoid homeostasis and sex hormones of adult male European common frogs (Rana temporaria).

Reports of declining numbers of species and individuals of amphibians in most parts of the world have caused great concern. Several causative factors have been linked to this amphibian decline, and increased environmental pollution related to pesticide use seems to be one important factor. Persistent organic pollutants may act as endocrine disrupters, and thereby exert adverse effects on development (metamorphosis, growth and sexual differentiation) in amphibians. During periodic events, such as spring snowmelt, amphibians may be exposed to acute high levels of pesticides. 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolite 1,1-dichloro-2,2-bis(p-chlorophenyl)ethene (p,p'-DDE) is a pesticide that is still found in wetlands and soils. In order to study the effects of p,p'-DDE on susceptible amphibian endocrine systems, adult male European common frogs (Rana temporaria) were exposed to different doses of p,p'-DDE (0, 0.01, 0.1, 1 and 10 mg p,p'-DDE/kg body mass) for 14 d and sex hormone levels (testosterone and 17beta-estradiol) in plasma and retinoid concentrations (retinol and retinyl palmitate) in liver were determined. The results showed a significant variation in the liver retinol concentration at increasing doses of p,p'-DDE, suggesting that p,p'-DDE may interfere in the hepatic metabolism of retinol in adult frogs. Lack of effects on sex hormones may indicate that after arousal from hibernation males are relatively resistant to adverse reproductive effects of p,p'-DDE.