Morphologic changes in the rat uterus following natural mating and embryo transfer

In order to gain some insight into the putative immune suppression that may be induced at the placental implantation sites, the morphological changes at these sites following natural matings and following the transfer of embryos fertilized in vivo were studied. The only histologic parameter that showed a significant difference was the number of granulated metrial gland (GMG) cells. More GMG cells were present in allogeneic than in syngeneic pregnancies, and more GMG cells were present following embryo transfer into an allogeneic female than following the comparable natural mating. The role of the GMG cells in pregnancy is, however, still unresolved.