Conversion of pregnenolone to progesterone by mouse morulae and blastocysts

When mouse morulae, early blastocysts and implanting blastocysts were cultured with tritiated pregnenolone, tritiated progesterone and its metabolites, 5 alpha-pregnan-3,20-dione and 3 alpha-hydroxy-5 alpha-pregnan-20-one, were isolated from the medium. It appears that mouse embryos can make progesterone from pregnenolone and the progesterone is quickly metabolized into various metabolites. These abilities increase with development. It is suggested that the mouse embryo can make progesterone and may regulate its own progesterone level for optimal development.