IN-VITRO MOLECULAR ASSESSMENT OF THE MECHANISMS OF ACTION OF 19-NOR PROGESTINS USED AS CONTRAGESTATIONAL AGENTS

Norethisterone (NET) and levonorgestrel (LNG) are synthetic progestins used as contragestational agents, Both compounds are biotransformed a t target tissues into A-ring reduced metabolites which possess differe nt pharmacological properties, The aim of this study was to determine the molecular mechanisms of the progestational and antiprogestational effects of NET, LNG and their metabolites by using a highly efficient, sensitive in vitro molecular assay based on the detection of a report er gene expression (the bacterial chloramphenicol acetyltransferase (C AT) inserted downstream of a minimal promoter containing two progester one responsive elements (PRE2) and the TATA box. For this purpose we u sed CV-1 monkey kidney cells, which do not possess steroid receptors. These cells were cotransfected with a progesterone receptor expression vector and the reporter vector PRE(2)-TATA-CAT. Data obtained using t his model showed that NET and LNG induced CAT activity in a manner sim ilar to that of the potent progestin R5020. NET and LNG metabolites ex hibited a weak progestational activity; however, when 5 alpha-NET meta bolite was simultaneously administered with R5020, a clear antiprogest ational effect similar to that of the antiprogestin RU486 was observed . Therefore, the results clearly demonstrate that the use of the repor ter CAT vector containing hormone responsive elements is a suitable as say for the screening and evaluation of new synthetic steroids with ag onist or antagonist progestational activities in transfected CV-1 cell line.