Description:
<jats:p>A number of metabolites of 17β‐estradiol were tested for their estrogenic activity using the ER‐CALUX assay based on the increased expression of luciferase in exposed T47D breast cancer cells. E<jats:sub>2</jats:sub>β and estrone showed similar potencies in the test, whereas E<jats:sub>2</jats:sub>α was 100 times less active. Incubation of cells with estrone (0.35 μM) resulted in the formation of E<jats:sub>2</jats:sub>β, whereas the reverse reaction was observed for E<jats:sub>2</jats:sub>β. The resulting equilibrium may explain the similar estrogenic potency of estrone in the test. The synthetic 17‐hydroxy benzoate ester of E<jats:sub>2</jats:sub>β was 3 times less active than the parent compound. The 17‐hydroxy palmitate and oléate esters of E<jats:sub>2</jats:sub>β, were respectively 25 and 200 times less active than the parent compound. The 2‐hydroxy metabolites of E<jats:sub>2</jats:sub>β and estrone showed a 5,000 to 10,000 fold lower activity. The 4‐hydroxy metabolites were more potent than the 2‐hydroxy metabolites, showing only a 20–200 times lower activity. The 2‐ and 4‐methoxyesters of estrone were 700 times less active. It is concluded that the estrogenic potency of metabolites formed in cattle after treatment with E<jats:sub>2</jats:sub>β, like estrone, E<jats:sub>2</jats:sub>α and especially the esters of E<jats:sub>2</jats:sub>β, may be significant with respect to the potential risk of the use of estradiol for growth promotion in domestic animals in certain countries.</jats:p>