Effect of cadmium (Cd++) on rainbow trout (Oncorhynchus mykiss) estrogen receptor biological activity.

Numerous publications have related the negative action of cadmium (Cd++) on vitellogenesis in fishes. This action is not clearly established. The aim of the present study was to determine if the cadmium-mediated decrease of v itellogenesis was a process interfering with the rainbow trout estrogen rec eptor (rtER) activity. The effect of cadmium rtER activity was studied in a recombinant yeast system expressing highly and stably rtER and in trout he patocyte cultures. In yeast system, rtER activated by estradiol (E2) regula tes specifically the expression of the beta-Galactosidase reporter gene. Th e E2-stimulation of the reporter gene expression was reduced by 45% under 1 0 mu M Cd++ treatment. In rainbow trout hepatocytes cell culture, the vitel logenin (VTG) gene expression, positively regulated by E2, was also reduced by 65% after Cd++ treatment. Cadmium does not affect the estradiol binding capacity of the receptor and only the hormone-dependent activity of rtER w as affected by this metal. This study shows that the negative effect of Cd+ on estradiol action was probably mediated by a direct effect on the hormo ne-dependent transactivation function of rtER.