Assay of estrogens in human feces

A radioimmunological method for the determination of unconjugated and conjugated estrone (E1), estradiol (E2) and estriol (E3) in feces of women and men is described and validated. Positive proof of specificity was obtained by GC/MS identification of the three estrogens in feces of a non-pregnant woman. In addition estradiol-17 alpha was detected in the estradiol fraction and an unknown tetrol in the E3 fraction. It is shown that the method fulfills the reliability criteria and that it is possible to measure these estrogens in 1 g feces samples. Estrogen excretion varies during the menstrual cycle with the greatest excretion around ovulation time. The relative amount of E2 is much higher in feces than in urine and bile reflecting reductive metabolism in the gut. About 10-15% of E1, E2 and E3 occurs in the conjugated form in feces. Quantitative data for young women during the menstrual cycle, for postmenopausal women and for men are presented. Men and postmenopausal women excrete similar amounts of estrogen in feces, but during the menstrual cycle much higher concentrations are found. Calculations reveal that fecal excretion of these estrogens represents about 5-10% of total excretion of estrogens in urine and feces. It is concluded that estrogen metabolism in the intestinal tract may be of similar biological significance to that in the liver.