CIRCULATION OF ESTROGENS INTRODUCED INTO THE RECTUM OR DUODENUM IN PIGS

To determine the absorption and metabolism of 17 beta-estradiol (E(2)) by the rectum of the pig, 10 mg of crystalline E(2) was placed in the rectum of prepubertal gilts in Experiment 1. Blood samples were subse quently obtained from hepatic portal and jugular veins and plasma was assayed for E(2), estrone (E(1)), 17 beta-estradiol-glucuronide (E(2)G ), estrone-glucuronide (E(1)G) and estrone-sulfate (E(1)S). Concentrat ion of E(2), E(1), E(2)G, E(1)G, and E(1)S rose in the hepatic portal vein within 30 min and remained elevated for several hr. Concentration s of E(2) in the hepatic portal vein represented 3% of the total estro gen detected in the hepatic portal vein during the 5 hr sampling perio d, indicating that most of the E(2) was metabolized prior to entering the hepatic portal vein after absorption by the rectal mucosa. Concent rations of E(2), E(1), E(2)G, E(1)G, and E(1)S rose in the jugular vei n and remained elevated for several hr. The rise in E(2) and E(1) in t he jugular vein may have come from E(2) and E(1) in venous circulation from the rectum that entered the inferior vena cava bypassing the hep atic portal vein and liver. The net result of absorption of E(2) from the rectum of gilts was a large rise in unconjugated and conjugated E( 2) and E(1) in the peripheral circulation. In Experiment 2 prepubertal gilts fitted with jugular, hepatic portal, duodenal, and gall bladder catheters were infused into the duodenum with bile from pregnant gilt s. Concentrations of E(2), E(1), E(2)G, and E(1)G were determined in g allbladder bile of gilts before infusion and at 470 min. Concentration s of E(2)G and E(1)G were determined in hepatic portal and jugular pla sma before and after infusion of bile. A cholagogue was given at 480 m in and E(2)G and E(1)G were measured in plasma from 490 min to 960 min . Concentrations of E(2) and E(1) in gallbladder bile rose at 470 min and fell to basal concentrations at 970 min. In gilts given the cholag ogue, E(2)G and E(1)G in both the jugular and hepatic portal veins ros e significantly over those in gilts not given the cholagogue. Bile est rogens circulate via the enterohepatic route and factors that influenc e secretion of estrogens in bile can influence concentrations of circu lating estrogens.