Enterohepatic Metabolism of Estriol-3-sulfate-16-glucosiduronate in Women1

Abstract

The metabolism of estriol-3-sulfate-16-glucosiduronate (E₃-3S,16G), the major biliary metabolite of estriol (E₃), was studied in human subjects in 2 types of experiments. In the first type, labeled E₃-3S, 16G was injected into the duodenum (via the T-tube) of 2 subjects with bile fistulas and the biliary and urinary metabolites were identified and quantitated. An average of 53 % of the radioactivity was excreted in the urine and 23 % in the bile. The biliary conjugates consisted mainly of E₃-3S, 16G. Lesser amounts of E₃-16G but no E₃-3G were found. The urine contained E₃-3G, lesser amounts of E₃-16G, but no E₃-3S,16G. Following the intravenous injection of E₃-3S,16G into intact subjects (second type of study), the nature of the urinary conjugates changed with time. In the early hours of the study E₃-3S,16G and E₃-16G predominated, while E₃-3G was absent. Later, the level of E₃-3S,16G declined, while E₃-3G appeared in significant amounts. These data are consistent with the following proposed pathway for the intermediary metabolism of biliary E₃-3S,16G. The bulk is efficiently reabsorbed by the intestine. In the process a large part of the E₃-3S,16G is converted into E₃-3G, of which the preferred route of excretion is the urine. The intestine also releases E₃-16G into the liver via the portal circulation. Most of the E₃-16G is excreted in the urine and a minor part into the bile. The liver converts some of the E₃-16G into E₃-3S,16G which is secreted mainly in the bile.