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

To determine the absorption and metabolism of 17β-estradiol (E₂) by the stomach and liver of the pig, crystalline E₂ 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 E₂, estrone (E₁), 17β-estradiol-glucuronide (E₂G), estrone-glucuronide (E₁G) and estrone-sulfate (E₁S). Concentrations of E₂, E₁, E₂G and E₁S rose in the hepatic portal vein within five min and remained elevated for several hr. Concentration of E₂ represented only 6% of the total estrogen detected in the hepatic portal vein during the sampling period, indicating that most of the E₂ was converted or conjugated prior to entering the hepatic portal vein. The metabolism of E₂ presumably occurred in the stomach mucosa because food had been withheld for 26 hr before infusion of E₂. Concentrations of E₂G, E₁G and E₁S, but not E₂ and E₁, rose in the jugular vein and remained elevated for several hr. The lack of a rise in E₂ and E₁ in the jugular vein indicates that the E₂ and E₁ from the hepatic portal vein were completely converted and/or removed by the liver. Most of E₂ was converted to E₁ and then to E₁G. The infusion of bile containing normal estrogens from pregnant gilts into the duodenum of prepubertal gilts resulted in a peak of E₁G and E₂G 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 E₁ and E₂ from the bile before infusion. The second peak failed to occur in gilts given antibiotics orally to reduce gut bacteria before infusion of bile.