Results indicate the primary site of progesterone metabolism is the liver.
Summary Heifers were used to evaluate progesterone metabolism in the liver and brain during the estrous cycle. Blood samples were collected from the carotid artery and jugular, portal and hepatic veins. Progesterone concentrations in the hepatic vein were less than in portal and jugular veins and the carotid artery, but there were no differences between the carotid artery and jugular and portal veins. During the estrous cycle much of the progesterone in blood is metabolized by the liver. The amount of any hormone in circulation is regulated by the rate of hormone release from the endocrine gland and the rate of hormone degradation in the organs that metabolize it.