Steroid metabolism by rabbit embryos: time of onset of steroidogenic activity

Twenty four hour incubations of the days 5 and 6 pre-implantation and the days 7 and 8 post-implantation rabbit embryos were carried out in the presence of 3H-labelled steroid substrates viz. dehydroepiandrosterone (DHEA), androstenedione (Ad) and testosterone (Te). While both the pre- as well as the post-implantation embryos were able to actively metabolize the various neutral steroid substrates into other neutral, mostly 5 alpha-reduced, steroid metabolites, the conversion of DHEA to Ad or that of DHEA, Ad and Te to estrogens was exhibited only by the days 7 and 8 post-implantation embryos. The findings suggest that pre-implantation blastocysts of rabbit lack the potentiality to synthesize steroids and acquire this ability only after implantation.