INVITRO METABOLISM OF 17-ALPHA-ETHYNYLSTEROIDS

The rates of metabolism of synthetic gestagens derived from 19-nortestosterone by rabbit liver tissue in vitro were compared. Over a period of 1 h norethisterone was metabolised as rapidly as 19-nortestosterone whereas d-norgestrel and lynestrenol were metabolised at a slightly lower rate. Less than 5% of l-norgestrel was metabolised. In all cases the reaction product was the tetrahydrosteroid. Lynestrenol was metabolised through norethisterone. Skeletal muscle, lung and small intestine also metabolised norethisterone and d-norgestrel but at a slower rate than liver tissue. Small amounts of norethisterone were metabolised by adipose tissue but heart and spleen were inactive. Lynestrenol and l-norgestrel were not metabolised by any of the extra-hepatic tissues studied. © 1979.