Context: The 17beta-estradiol fatty acid esters are hormone derivatives with long-lasting estrogenic effect. They are transported in serum lipoproteins and thought to be sequestered in adipose tissue.
Objective: Our objective was to determine the 17beta-estradiol fatty acid ester concentrations in serum and adipose tissue in women of various hormonal states.
Design: After several chromatographic steps separating esterified from free estradiol, time-resolved fluoroimmunoassay was used as a quantifying tool.
Participants: Samples were obtained from pregnant women undergoing cesarean section (n = 13), or premenopausal (n = 8) and postmenopausal women (n = 6) during gynecological surgery.
Main outcome measures: 17beta-Estradiol and 17beta-estradiol fatty acid ester concentrations in serum, and visceral and sc adipose tissue were examined.
Results: The ratio of esterified to free estradiol in plasma increased with decreasing estradiol level from 0.5% in pregnant, to 15% in premenopausal and 110% in postmenopausal women. Estradiol esters constituted about 10% of the free estradiol present in adipose tissue in pregnancy. In nonpregnant women, most of the adipose tissue estradiol was in esterified form, the median ester to free ratio being elevated to 150-490%. After menopause, the overwhelming majority of estradiol in both free and esterified form was present in adipose tissue.
Conclusions: The overall higher ester to free estradiol ratio in adipose tissue than in serum indicates active esterification capacity in adipose tissue. The predominance of esterified and free estradiol in postmenopausal adipose tissue compared with serum suggests in situ production and storage. Whether the estradiol esters have an independent physiological role in adipose tissue remains to be clarified.