Polychlorinated biphenyls, sex steroid hormones and liver retinoids in adult male European common frogs Rana temporaria

Declines in amphibian populations and species biodiversity during the last decades has called for an assessment of possible threats to these animals. Polychlorinated biphenyls (PCBs) are known endocrine disrupting contaminants and are found in high levels in some populations of wild living amphibians. To evaluate the endocrine disrupting potential of PCBs in adult frogs, Aroclor 1254 were subcutaneously injected into male European common frogs Rana temporaria. The injected doses ranged from 0.01 to 100 mg/kg body mass, resulting in liver concentrations between 74 and 133 619 μg/kg ww. After 14 days, serum testosterone (T), estradiol (E) and hepatic retinol (R) and retinylpalmitate (RP) were easured. No dose dependent effects were found on levels of hormones or retinoids. However, a significantly higher within-group variation in the E–T ratio in the exposed groups may indicate that the sex-hormone homeostasis of male R. temporaria is affected by PCBs shortly after arousal from hibernation, but that the effects are subtle and that several different mechanisms are involved. The lack of direct effect on T, E, R and RP may be due to the timing of exposure (shortly after arousal from hibernation), or due to a relatively short exposure time to Aroclor 1254. Based on the results, we propose that future research should focus on effects of PCBs in relation to the different physiological phases frogs experience throughout the year (hibernation, reproduction etc.).