Quantitative determination of estradiol fatty acid esters in human pregnancy serum and ovarian follicular fluid

Background: Lipophilic estradiol derivatives carried by lipoprotein particl es in blood may mediate antioxidant or endocrine effects. We developed a ne w quantitative method to determine the concentration of circulating lipophi lic estradiol fatty acid esters in human early- and late-pregnancy serum an d in ovarian follicular fluid. Methods: After extraction from serum or follicular fluid, estradiol fatty a cid esters were separated from nonesterified estradiol by Sephadex LH-20 co lumn chromatography. The estradiol ester fraction was hydrolyzed by saponif ication and further purified by several chromatographic steps. The hydrolyz ed estradiol esters were measured by time-resolved fluoroimmunoassay. Results: The average estradiol fatty acid ester concentration in serum incr eased 10-fold during pregnancy, from 40.4 pmol/L (expressed as pmol/L estra diol; range, 25.0-64.2 pmol/L) in early pregnancy (n = 8) to 404 pmol/L (19 6-731 pmol/L) in late pregnancy (n = 10). The ratio of estradiol ester to n onesterified estradiol remained relatively constant during pregnancy, at 0. 4-0.6%. In 10 follicular fluid samples, the mean estradiol ester concentrat ion was 106 nmol/L (56.9-262 nmol/L). Compared with serum, a greater propor tion of estradiol in follicular fluid (3.0-10%) was in the esterified form. Conclusion: The new method provides a means to measure circulating estradio l fatty acid ester concentrations in human pregnancy serum. (C) 2001 Americ an Association for Clinical Chemistry.