Estimation of Proteolytic Activity at Mouse Implantation Sites by the Gelatin Digestion Method

Summary. A faint proteolysis without any appreciable peak intensity on Days 5 to 9 of normal pregnancy surrounds the implantation sites in mice. Neither the antimesometrial trophoblastic zone nor the ectoplacental cone showed more activity than the rest of the tissue. Uterine epithelium during this period showed a slightly stronger and more distinctly localized proteolysis. No epithelial activity was found during early pregnancy. Day-4 blastocysts, studied in vitro, showed no activity. It is concluded that the uterine epithelium at the time of implantation has an intrinsic ability to undergo autolysis and that the autolysis can be elicited by the trophoblast.