Role of intrauterine environment in the disappearance of eggs in rats bearing an IUD

Experiments were done in rats with the purpose of gaining insight into the mechanism by which eggs disappear from the uterine lumen in the presence of an IUD. On day 4 of pregnancy a ligature was placed either between the IUD and the cervix or between the IUD and tubo-uterine junction, so as to divide the uterine lumen in two portions. Autopsy was done on day 5 to determine the number and state of the eggs in the uterus. It was found that eggs disappear when they enter the portion containing the IUD, but they stay intact when they enter into the portion with the IUD excluded by the ligature. The results support the concept that the uterine segment in direct contact with the IUD confers lytic properties upon the intrauterine fluid which diffuse throughout the lumen and cause the disintegration of the eggs.