are estrogen receptor antagonists, ie. they block or interfere with
the estrogen receptor. Tamoxifen is a synthetic antiestrogen (although
with agonist properties as well) used to treat breast cancer because
of its ability to inhibit the breast cancer cell proliferation.
estrogen is critical to not only the regulation of the reproductive
system, but to growth, bone development, and metabolism, the suspected
effects of antiestrogens are numerous. Most endocrine disruption
research has focused on the reproductive impacts of antiestrogens,
which are typically identified by their ability to inhibit the proliferation
of the human breast cancer cell.
and some hydroxy-PCB congeners have reported anti-estrogenic effects.
It is important to note, however, that dioxin is not an antiestrogen
at the receptor level in that it does not bind to the estrogen receptor.
Rather, dioxin modulates estrogen's effect, and depending on the
the time of exposure, dose and targeted tissue, can have a variety
of effects. Antiestrogenicity is one of these effects. Dioxin has
been shown to suppress the 17-ß estradiol dependent-growth
of human breast cancer cells. Dioxin's estrogen antagonism is believed
to be the result of 'cross talk' interaction between the Ah receptor,
for which dioxin has a high affinity, and the estrogen receptor(s).
Ah receptor agonists including dioxin, PCBs and hexachlorobenzene
all have anti-estrogenic effects. In carp, dioxin has been shown
to inhibit the production of vitellogenin, the yolk protein precursor,
in female fish. More