Steroid Hormone Action Sex steroids are characterized by their affinity for specific estrogen, progesterone, or androgen receptors, and by their biologic effects in different systems (108). Steroids are rapidly absorbed in the gut but go directly into the liver through the portal circulation, where they are rapidly metabolized and inactivated. Therefore, large doses of steroids are required when they are administered orally. The addition of the ethinyl group to carbon-17 of the steroid molecule hinders degradation by the liver enzyme 17-hydroxysteroid dehydrogenase and allows potent biological activity after oral doses of only micrograms.