Concentrations of free steroids in the jugular and hepatic portal veins of pigs after ingestion of testosterone, estrogen, or progesterone or transplantation of ovaries to the intestine.

Estrogen, progesterone or testosterone were administered orally to ovariectomized gilts fitted with indwelling catheters. Blood samples were taken from the jugular and hepatic portal veins at intervals varying from a few minutes to daily over periods that varied from 1 d to several months. Concentrations of free steroids rose dramatically in the hepatic portal vein within a few min of feeding steroids and remained high for 3-8 hr before declining to base levels. Concentrations in the jugular vein sometimes rose very slightly for the same period. At 48 hr after administration the concentrations remained at baseline in the hepatic portal vein, but rose several-fold in the jugular and remained elevated for several days. Autotransplantation of the ovaries to the intestine resulted in very large ovaries consisting of many large, heavily luteinized cystic follicles. Concentrations of progesterone and estrogen in the hepatic portal vein were very high, but were low in the jugular vein. The gut wall allows for passage of some orally administered free steroids to the liver via the hepatic portal vein. The free steroids are essentially metabolized before they reach the jugular vein, but can be recirculated via the enterohepatic route.