Long-term exposure investigating the estrogenic potency of estriol in Japanese medaka (Oryzias latipes)

Abstract

The growth, development, and ERα and Vtg-I gene expressions of Japanese ricefish (Oryzias latipes; medaka) exposed to different concentrations of estriol (E3), including one environmentally relevant concentration, during embryo-adult life stages were evaluated. At the early life stage, fertilized eggs were exposed to 5, 50, 500, 5000ng/L E3 for 15days, and the hatched fry were exposed continuously to the same concentrations for an additional 15days. Exposure to 500 and 5000ng/L E3 resulted in adverse effects on hatchability and time to hatching. At 5000ng/L, the gross abnormality rate was increased and the number of females that hatched was twice that of males. When the fish were exposed to 5–5000ng/L E3 for further 60days, the male hepatosomatic index (HSI) was increased at 5000ng/L. The female gonadosomatic index (GSI) was decreased at 500 and 5000ng/L E3, while the male GSI at 5000ng/L E3 was increased and sex reversal was also found at this concentration. Quantitative RT-PCR showed that the hepatic vitellogenin-I (Vtg-I) genes were up-regulated in females at 500 and 5000ng/L E3 and in males at all E3 concentrations, whereas E3 did not affect estrogen receptor α (ERα) mRNA transcription. These results showed that E3 at environmental concentration of 5ng/L has no adverse effects on growth and development of the Japanese medaka. However, in this study, if we only focused on Vtg gene change in males, E3 had strong estrogenic effects on male medaka under the conditions of these experiments.