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There is a growing awareness that androgens and estrogens have
general metabolic roles that are not directly involved in reproductive
processes. These include actions on vascular function, lipid and
carbohydrate metabolism, as well as bone mineralization and epiphyseal
closure, in both sexes. In postmenopausal women, as in men, estrogen is
no longer solely an endocrine factor, but instead is produced in a
number of extragonadal sites and acts locally at these sites in a
paracrine and intracrine fashion. These sites include breast, bone,
vasculature, and brain. Within these sites, aromatase action can
generate high levels of E2 locally without significantly affecting
circulating levels. Circulating C19 steroid precursors are
essential substrates for extragonadal estrogen synthesis. The levels of
these androgenic precursors decline markedly with advancing age in
women, possibly from the mid to late reproductive years. This may be a
fundamental reason why women are at increased risk for bone mineral
loss and fracture and possibly decline of cognitive function, compared
with men. Aromatase expression in these various sites is under the
control of tissue-specific promoters regulated by different cohorts of
transcription factors. Thus, in principle, it should be possible to
develop selective aromatase modulators that block aromatase expression,
for example, in breast, but allow unimpaired estrogen synthesis in
other tissues such as bone.