Estradiol fatty acid esters. The isolation and identification of the lipoidal derivative of estradiol synthesized in the bovine uterus.

The bovine uterus, like other estrogen-responsive organs of man and rat, synthesizes an unusual nonpolar metabolite of estradiol (Schatz, F., and Hochberg, R. B. (1981) Endocrinology 109, 697-703). This compound, the lipoidal derivative of estradiol (LE2), was synthesized from estradiol by bovine endometrial tissue in vitro, and it was purified by extensive chromatography on two adsorption columns, a reversed phase partition celite column and three different high pressure liquid chromatography columns. LE2 was separated into nine fractions which were analyzed by direct probe mass spectroscopy and by gas chromatography mass spectroscopy after cleavage of the lipoidal moieties. In this manner, 10 fatty acid esters of estradiol, exclusively esterified at C-17 of the steroid nucleus, were identified. The unsaturated fatty acid esters of estradiol comprise more than 85% of the total LE2 and estradiol 17 beta-arachidonate is the most abundant component. The cholesterol esters and phospholipids of the bovine endometrium were also purified and it was found that the distribution of fatty acids in these lipids is far different from that of LE2.