Estriol conjugates in human breast cyst fluid and in serum of premenopausal women

A sensitive method was developed for the assay of the lour major estriol (E₃) conjugates in human breast cyst fluid and in serum during the menstrual cycle. In the cyst fluid, estriol-3-sulfate (E₃-3S) was found in each of ten samples, the concentrations ranging from 240-4310 pg/ml. Estriol- 16-glucosiduronate (E₃-16G) was detected in six samples at levels of 19-153 pg/ml; estriol-3-glucosiduronate (E₃-3G) in five samples, 13-79 pg/ml and estriol-3-sulfate-16-glucosiduronate (E₃-3S-16G) in four samples, 28-152 pg/ml. Unconjugated estriol was found in three of the ten cases (12-30 pg/ml). Serum samples obtained in the follicular and luteal phases of the cycle from eight different subjects were assayed in the same way. There was considerable variation between subjects and many values were indistinguishable from zero. But preliminary data suggest that E₃-3G is the predominant E₃ conjugate in the serum and E₃-3S-16G is quantitatively least important. It appears that E₃ conjugates in the cyst fluid are not derived from the blood directly, but are produced locally from precursors which have not been identified.