The role of progesterone in implantation and trophoblast invasion.

With its genomic and non-genomic actions, progesterone plays a role in preparing the endometrium for implantation and also in regulating trophoblast invasion and migration. The genomic actions of progesterone are mediated by the classical nuclear progesterone receptors, PR-A and PR-B. In addition to their genomic actions, nuclear progesterone receptors may also trigger rapid cytoplasmic signalling events. Membrane-bound progesterone receptors have been implicated in the rapid non-genomic actions of progesterone. Both genomic and extra-nuclear actions of progesterone are crucial for adequate decidualisation and implantation. Progesterone plays a role in establishing uterine receptivity by blocking the proliferative effect of oestrogen, by inducing genes that allow the endometrium to permit embryo attachment, and also acts as a negative regulator of trophoblast invasion by controlling matrix metalloproteinase (MMP) activity.