Absorption and metabolism of estrogens from the stomach and duodenum of pigs

Abstract

To determine the absorption and metabolism of 17β-estradiol (E 2) by the stomach and liver of the pig, crystalline E 2 was placed in the stomach of prepubertal gilts. Blood samples were subsequently obtained from the hepatic portal and jugular veins and plasma was assayed for E 2, estrone (E 1), 17β-estradiol-glucuronide (E 2G), estrone-glucuronide (E 1G) and estrone-sulfate (E 1S). Concentrations of E 2, E 1, E 2G and E 1S rose in the hepatic portal vein within five min and remained elevated for several hr. Concentration of E 2 represented only 6% of the total estrogen detected in the hepatic portal vein during the sampling period, indicating that most of the E 2 was converted or conjugated prior to entering the hepatic portal vein. The metabolism of E 2 presumably occurred in the stomach mucosa because food had been withheld for 26 hr before infusion of E 2. Concentrations of E 2G, E 1G and E 1S, but not E 2 and E 1, rose in the jugular vein and remained elevated for several hr. The lack of a rise in E 2 and E 1 in the jugular vein indicates that the E 2 and E 1 from the hepatic portal vein were completely converted and/or removed by the liver. Most of E 2 was converted to E 1 and then to E 1G. The infusion of bile containing normal estrogens from pregnant gilts into the duodenum of prepubertal gilts resulted in a peak of E 1G and E 2G in the hepatic portal and jugular veins within a few minutes. This was followed in about 180 min by a second sustained rise. The first peak was essentially abolished by extracting E 1 and E 2 from the bile before infusion. The second peak failed to occur in gilts given antibiotics orally to reduce gut bacteria before infusion of bile.