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Effect of physical enlargement of the cervical lumen on the preimplantation loss of eggs in rabbits.

The function of the cervix in holding embryos in the uterine cavity during early pregnancy was re-evaluated in rabbits in which cervical devices had been installed to expand the cervical lumen. The cervical device, consisting of either intact (Type A) or fenestrated (Type B) polyethylene tubing (intracervical part) attached to a base of sili-cone rubber, was inserted into a unilateral cervical canal. The animals were mated and given an iv injection of hCG (20 IU), and examined for fertilization, implantation and loss of eggs.The devices installed in the cervix did not interfere with fertilization, implantation and sperm transport, although the implantation rate was low on the side in which Type-B devices had been installed. At autopsies performed 3 to 5 days post coitum (p.c.), the reproductive tract was flushed and the embryos were examined. A significant (P<O.05) loss of ova on day 5 p. c. was observed on the side containing Type-B devices. In vivo vaginal washing conducted in intact does 48 to 168 h p. c. revealed that about 10% of the eggs ovulated had been expelled into the vagina during the preimplantation stage.The present findings indicate that a structural characteristic of the cervix, namely the narrow lumen, contributes to prevention of egg expulsion, and that the expulsion mecha-nism may depend on some function of the cervical epithelium, probably ciliary action.