Al and Cd-induced inhibition of vitellogenin (VTG) production was examined at the estrogen receptor (ER) level in rainbow trout Oncorhynchus mykiss hepatocytes. The binding of $[^3H]$ $estradiol-17eta;(E_2)$ to hepatocytes reached a plateau 3 days after addition of $E_2;(2 imes;10^{-6} M)$to the medium. The binding activity was linearly reduced with the increased concentrations $(-10^{-5};M)$ of 4-hydroxy-tamoxifen (4-OHT) and specific binding linearly increased with the increased doses of $[^3H];E_2$, indicating that the radioligand bound to ER. Al $(-10^{-4};M)$and Cd $(10^{-6};M)$ as well as 4-OHT $(10^{-6};M)$ significantly reduced the $[^3H];E_2$-binding activity by $3040\%$, while they completely inhibited VTG production. Al and Cd had no effect on $E_2-human$ $ERalpha$ binding activity at any concentrations used $(-10^5;nM;each)$. These results suggested that Al and Cd inhibited VTG production in part by interfereing with the ER level. Inhibitory effects of these metals on the $E_z-dependent$ upregulation of ER activity are also discussed.
