Abstract
ABSTRACT The metabolism of oestradiol-16-14C,17α-3H and oestriol-16-14C,16β-3H was studied following the intravenous administration of each compound to two women at midgestation. In addition, the foeto-placental metabolism of oestriol-16-14C,17α-3H was investigated in a subject following the administration of the tracer into the umbilical circulation at laparotomy. The 3H/14C ratios of urinary, foetal and placental oestriol conjugates were estimated following reverse isotope dilution of the oestriol moiety and its triacetate. The 3H/14C-ratios of the oestriol-16-glucosiduronate (OE3-16GL) and oestriol-3-sulphate,16glucosiduronate (OE3-3S,16GL) fractions isolated from all urine specimens, as well as those of unconjugated oestriol (OE3), oestriol-3-sulphate (OE3-3S) and OE3-16GL isolated from the foeto-placental unit did not differ from each other and agreed with that of the administered material. Also, the 3H/14C-ratio of the oestriol-3-glucosiduronate (OE3-3GL) isolated from the urine excreted during the first 24 h, agreed with those of the other conjugates. However, a statistically highly significant drop was found in the 3H/14C-ratio of the OE3-3GL isolated from the second and third 24 h urine collections. Relatively more 3H was lost from oestriol-16β-3H, than from oestriol-17α-3H. It is concluded that OE3-3GL underwent a limited oxidation both at C-atoms 16 and 17. This oxidation seems to take place in the gastrointestinal tract and might be due to the activity of microorganisms. It is suggested that the same steroid molecule present in the form of various conjugates may be metabolized differently.
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