Up-regulation of estrogen receptor mRNA and estrogen receptor activity by estradiol in liver of rainbow trout and other teleostean fish

Injection of estradiol (E₂) into immature rainbow trout resulted in the induction of the hepatic vitellogenin gene mediated by the nuclear estrogen receptor (ER). Liver ER mRNA rose markedly on E₂ treatment in three groups of trout kept at different temperatures. Only in the group kept at 4°C did the total cellular ER, as measured by [³H]estradiol-binding activity in nuclear and cytosol fractions, parallel the ER mRNA level. In fish kept at 9°C and 15°C, the ratio of total ER activity to ER mRNA fell during chronic E₂ treatment, probably reflecting translational or post-translational control mechanisms. Upregulation of ER mRNA also occurred in sea raven, sculpin, winter flounder, and Atlantic salmon after E₂ treatment. Intrahepatic ER activity rose proportionately in Atlantic salmon kept at 6-9°C but not in sea raven, sculpin, or flounder. We conclude that the regulation of ER expression in teleosts is complex and includes transcriptional, translational, and posttranslational elements and is influenced by environmental temperature.