
Originally Posted by
MR10X
AROMATASE ACTIVITY IN ADIPOSE TISSUE
Aromatase is an enzyme present in many tissues, but particularly
in adipose tissue. Specifically, this enzyme, aromatase
cytochrome P450, is encoded by the CYP19 gene.23 This
converts androgens to oestrone and oestradiol.
Adipose tissue contains adipocytes that carry the accumulated
fat burden itself, as well as stromal cells, which are relatively
thinly dispersed blood vessels and fibroblasts. It appears
that 90% of the aromatase activity in fatty tissue is found in
the stromal cells, particularly the fibroblasts,24 although some
is also found in monocyte derived macrophages.25 Of some
importance is the fact that the fractional conversion of
androstenedione to oestrogens in obese subjects may not
decrease after weight loss, probably because the number of
stromal cells in the remaining adipose tissue does not appreciably
decrease.24 26 Furthermore, aromatase activity and its
expression in adipose tissue is markedly potentiated by
various promoters,27 as well as by the cytokine IL-6 and
tumour necrosis factor (TNF).28 29 Adipose stromal cells from
omental fat, but not subcutaneous fat, have been shown to
generate active cortisol from inactive glucocorticosteroids
through the expression of the enzyme 11-b-hydroxy steroid
dehydrogenase.30 These active glucocorticoids further encourage
aromatase activity.31 Other workers have shown that
aromatase activity, at least in subcutaneous adipose tissue, is
higher in men than women.32 The rate of conversion of testosterone
to oestrogen in omental tissue appears to be slower
than in other adipose tissue sites, although the final
concentrations of oestrogens in both sites are similar.24