A possible role of progesterone receptor in mouse oocyte in vitro fertilization regulated by norethisterone and its reduced metabolite

Background: The contraceptive effect of the progestogen norethisterone (NET) and its main metabolites 5 alpha-NFT and 3 beta,5 alpha-NET has been demonstrated in several species, and most studies have focused on the effects of these compounds in the uterus. We previously reported that 5 alpha-NET inhibits the progesterone (P-4)-induced acrosome reaction in pig and Mouse Spermatozoa and induces severe morphological damage in two-cell fertilized mouse oocytes. Study Design: The main goal of this study was to analyze the possible role of P-4 receptor (PR) in the effects of NET and 5 alpha-NET on the oocyte fertilization process. Different steroid treatments were used with or without cumulus-enclosed oocytes. Results: It was demonstrated that NET increases the percentage of fertilized oocytes in the same manner as P-4 does, while 5 alpha-NET reduces the percentage of fertilized oocytes. This effect was not reversed by P-4 in the same concentrations. Conclusion: A possible molecular mechanism for the effects of 5 alpha-NET may be through a PR localized in the oocyte plasma membrane. (C) 2008 Elsevier Inc. All rights reserved.