Additionally, PGE2 exhibits functions on immune cells that are not regulated by PGF2a (or PGI2) and that could be critical to maternal tolerance of the con-ceptus. Such functions include the differentiation of leukocytes into cells that are less lytic, more granulated, or that produce growth factors or Th2-type cytokines. It would be interesting to look at the spatio-temporal expression of both PGE synthase and PGF synthase in the endometrium to monitor any regulation in the expression of enzymes downstream of COX-2.
In summary, we propose that the up-regulation of COX-2 is beneficial in establishing pregnancy even if it is accompanied by higher PGF2a, because endogenous PGF2a is unable to trigger luteolysis at this time, probably because it lacks pulsatility and is counterbalanced by the concomitant increase in PGE2, which also has the potential to prevent immune rejection of the conceptus.
We report here that GM-CSF was localized on the bovine trophectoderm for only a short period, between d18P and d24P, in regions of the trophectoderm where attachment was not advanced. It was also found to be expressed in human and murine trophoblast, although it was undetectable in d17 ovine conceptus.