Adipose tissue estrogen production and metabolism in premenopausal women

Objective: Although the ovaries produce the majority of estrogens in women before menopause, estrogen is also synthesized in peripheral tissues such as adipose tissue (AT). The typical female AT distribution, concentrated in subcutaneous and femoro-gluteal regions, is estrogen-mediated, but the significance of estrogen synthesis in AT of premenopausal women is poorly understood. Design and Methods: Serum and subcutaneous and visceral AT homogenates from 28 premenopausal women undergoing non-malignant surgery were analyzed for estrone, estradiol, and serum estrone sulfate (E1S) concentrations with liquid chromatography-tandem mass spectrometry. Isotopic precursors were used to measure enzyme activities of estrone-producing steroid sulfatase and estradiol-producing 17?-hydroxysteroid dehydrogenases (17?-HSD). Messenger RNA (mRNA) expression levels of genes for estrogen-metabolizing enzymes were analyzed using real-time reverse transcription quantitative polymerase chain reaction. Results: While estradiol was the predominant circulating active estrogen, estrone dominated in AT, with a higher concentration in visceral than subcutaneous AT (median, 2657 vs 1459 pmol/kg; P = 0.002). Both AT depots converted circulating E1S to estrone, and estrone to estradiol. Median levels of estrone were five to ten times higher in subcutaneous and visceral AT than in serum (P