Our Absurd Fear of Fat

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63. Fat cells produce estradiol as well.

In postmenopausal women the median estradiol ester concentration also exceeded that of serum free estradiol. The very low serum levels of free and esterified estradiol in postmenopausal women compared with adipose tissue levels suggest that the vast majority of estradiol is produced and stored in adipose tissue in these women. This also indicates that the estradiol originating in adipose tissue is not effectively transported elsewhere. The estradiol ester to free estradiol ratio was higher in adipose tissue than in serum in all pregnant and postmenopausal women, and in all but one nonpregnant, obese premenopausal woman, indicating active esterification capacity in fat tissue.

The pathways for fatty acid esterification of estradiol as well as other steroid hormones have been observed in different organisms ranging from invertebrates, including insects, to vertebrates...The exact mechanisms of the endogenous formation of estradiol fatty acid esters are not fully known. In blood, estradiol fatty acid esters synthesized by LCAT circulate associated with lipoprotein particles, especially with high-density lipoprotein (12). It has been proposed that estradiol esters are formed in situ in various tissues by specific acyltransferases (1, 16, 17)...

In conclusion, estradiol esterification with fatty acids is relatively low during estrogen excess associated with pregnancy but increases with lower levels of circulating estradiol. In the postmenopause the overwhelming majority of estradiol is present in adipose tissue, mostly in the form of fatty acid esters. In contrast, serum esterified and free estradiol concentrations are low, suggesting that the effects of estradiol produced in adipose tissue are not systemic but local.

http://jcem.endojournals.org/content/92/11/4327.full