In vitro metabolism of catechol estrogens by human fecal microflora.

Intestinal bacterial metabolism of the catechol estrogens, 2-hydroxyestrone (2-OHE1), 2-methoxyestrone (2-MeOE1) and 2-hydroxyestradiol (2-OHE2), was studied by incubation of the steroid with mixed fecal flora. 3-Methoxyestrone (3-MeOE1) was included in order to evaluate whether demethylation occurs also with regard to noncatecholic estrogens. The purification of the samples and separation into fractions was carried out by ion exchange chromatography and the metabolites formed were identified by combined gas chromatography-mass spectrometry (GC-MS). Mixed human fecal flora was able to interconvert 2-OHE1 and 2-OHE2 both in aerobic and anaerobic conditions. Demethylation occurred both for 2-MeOE1 and 3-MeOE1.

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.

Identification of 4-hydroxyestriol in pregnancy urine.

After enzymatic hydrolysis and various chromatographic steps, an estrogen metabolite behaving like 4-hydroxyestriol in capillary gas chromatography on several stationary phases was detected in pregnancy urine. The mass spectrum of its trimethylsilyl ether derivative showed the very characteristic fragmentation pattern of catechol estrogens and was found to be practically identical with that of the corresponding derivative of the reference standard. In addition, selected ion monitoring evidence of the identity of the new estrogen metabolite with 4-hydroxyestriol was obtained. It is concluded that the results confirm previous studies indicating formation of 4-hydroxylated estrogen metabolites in human tissues.

Steroid absorption and enterohepatic recycling.

A short review on steroid absorption and enterohepatic recycling in man with special emphasis on contraceptive and related steroids is presented. Some new experimental data on the intestinal metabolism of steroids is described and includes further observations on the effect of antimicrobial agents on steroid hormone metabolism. Evidence is presented that plasma levels of steroids may be influenced if the intestinal microflora is altered. Some formation of biologically active steroids, like estradiol, may occur in the intestinal tract and this may have both biological and pathological consequences and may be influenced by such factors as diet and sex. It is concluded that our knowledge of the intestinal and especially, the mucosal metabolism of steroids is scanty and further studies are needed to clarify the role of the intestine and enterohepatic circulation in determining the bioavailability of natural and synthetic steroids.

PIP: The present knowledge on absorption and enterohepatic recycling of contraceptive steroids in human subjects is outlined and some recent results obtained are discussed in this review. The new experimental data relate to the effects of antimicrobial agents on steroid hormone metabolism The plasma levels of steroids may be influenced if the intestinal microflora are altered (as in antibiotic therapy). Some formation of biologically active steroids, such as estradiol, may occur in the intestinal tract and this may be consequential both biologically and pathologically, influenced by factors such as diet and sex. Knowlege of bioavailability of natural and synthetic hormones in terms of their metabolism in the intestine and enterohepatic circulation is scanty. Further studies are called for.