Rabbit endosalpinx suppresses ectopic implantation.

This study was undertaken to elucidate the mechanism underlying the absence of oviductal ectopic pregnancies in infraprimates. Endosalpingeal circumferential grafts were substituted for endometrium in a group of rabbits. The endosalpingeal grafts interfered with implantation as evidenced by four observations: (1) The nidation indices were lowered, (2) no implantations occurred on the grafted endosalpinx, (3) unattached blastocysts were found in animals grafted with endosalpinx, and (4) the implantation sites were significantly smaller in uterine horns containing endosalpingeal grafts. These findings suggest the presence of a factor in rabbit endosalpinx that actively suppresses ectopic implantation in the oviduct.