THE ISOLATION AND CHARACTERIZATION OF ESTRADIOL-FATTY ACID-ESTERS IN HUMAN OVARIAN FOLLICULAR-FLUID - IDENTIFICATION OF AN ENDOGENOUS LONG-LIVED AND POTENT FAMILY OF ESTROGENS

The estradiol-fatty acid esters are highly potent and long-lived estro gens that were first isolated and identified from in vitro biosyntheti c experiments (Mellon-Nussbaum S., Ponticorvo, L., Schatz, F., and Hoc hberg, R. B. (1982) J. Biol. Chem. 257, 5678-5684). Other studies have indicated that these esters exist endogenously, but the evidence is i ndirect, resting solely on the presence of a nonpolar saponifiable met abolite. Although there are similar reports of other naturally occurri ng fatty acid esters of biologically active steroid hormones, likewise , none has been isolated and characterized. In this study we have foun d that follicular fluid from the ovaries of women stimulated with gona dotrophins contains relatively large amounts of a nonpolar saponifiabl e derivative of estradiol (approximately 10(-7) M), which we presumed to be fatty acid esters. Using a combination of chromatographic techni ques we isolated these estradiol metabolites and identified them by ma ss spectral analysis. They are a mixture of five different estradiol-1 7 fatty acid esters, The amount of each present was determined by sepa rating the esters by reversed phase high performance liquid chromatogr aphy and then quantifying each peak by radioimmunoassay and UV absorpt ion. The esters of estradiol are predominantly unsaturated, with linol eate the most abundant comprising 43% of the total. The other esters a re: palmitate (20%), arachidonate (19%), oleate (14%), and stearate (4 %). Thus these studies conclusively demonstrate the existence of these unusually powerful estrogens.