In rats provided with a surgically created anastomosis between the two uterine horns and subsequently mated, implantation occurs with great regularity. Implantation sites were seen in twenty-six out of the thirty-two rats examined at laparotomy on Day 10 of pregnancy.
In rats with such an anastomosis and unilaterally ovariectomized, implantation occurred in both uterine horns. There was evidence of implantation in nine out of twelve rats in the left uterine horn, even though the left ovary had been removed, indicating that the anastomosis was patent.
Out of fifteen successfully mated rats with a connection between the two uterine horns and a silk suture in the lumen of the left uterine horn, only one rat showed evidence of implantation in the left uterine horn on Day 10 of pregnancy. There were no signs of implantation sites in the right horn in any animal in this series. The results demonstrated inhibition of implantation in the control horn when an intra-uterine device was placed in the experimental horn in rats with an anastomosis between the two horns. This suggests that the presence of a device in one horn led to the liberation of a substance which passed to the control horn through the surgically created anastomosis and there prevented implantation.