Regulation of estrogen receptors in primary cultured hepatocytes of the amphibian Xenopus laevis as estrogenic biomarker and its application in environmental monitoring.

The present study aims to introduce the regulation of estrogen receptors (ER) in primary cultured hepatocytes of the amphibian Xenopus laevis as a further potential estrogenic biomarker. Time courses of free ER in cell cultures treated with 17beta-estradiol (E2), nonylphenol (NP), and bisphenol A (BPA) were determined by means of radioreceptorassay (RARA). All compounds led to an immediate drop of free ER followed by a significant increase. The estrogen specific induction of ER-mRNA in vitro during time course was verified by using semiquantitative RT-PCR demonstrating greatest differences after 36 h. Dose-response curves of ER-mRNA for E2, NP, and BPA revealed that E2 possessed highest estrogenicity starting at 10(-9) M, while NP and BPA induced significant increases at 10(-8) and 10(-7) M, respectively. Extracts of the river Alb were subjected to RARA for ER binding to cytosolic liver fraction as well as to primary cultured hepatocytes for assessment of ER-mRNA induction. The results by RARA demonstrated clearly that binding to ER was highest in sewage treatment plant effluents and increased during the course of the river. These findings could be correlated with induction of ER-mRNA levels in vitro indicating that both techniques are suitable for application in monitoring of estrogenic EDC.