Timing of implantation in New Zealand White rabbits

Abstract

The timing of implantation was investigated in Kbl:NZW rabbits to assess the appropriate period of administration of test compounds recommended in the ICH Guideline for reproductive and developmental toxicity studies. After copulating in the morning (day 0 of gestation), pregnant rabbits were euthanized in the morning daily on days 6-9 of gestation. Their uteri were morphologically examined and the process of implantation was investigated. On day 6 of gestation, blastocysts had fixed their position in the uterine lumen for implantation, but they had not yet attached to the uterine mucosa. On day 7 of gestation, implantation sites were macroscopically recognized as protrusions of the uterine wall. Histological examination revealed that ob-placental implantation occurs in the antimesometrial region on days 7 and 8, while placental implantation occurs in the mesometrial region on days 8 and 9 of gestation. It was also found that organogenesis progresses in parallel with implantation.