Survival of embryos transferred into the IUD-bearing uterus of the rat

Mechanisms of action of intrauterine devices

The major effect of all intrauterine devices (IUD) is to induce a local inflammatory reaction in the endometrium whose cellular and humoral components are released into the uterine cavity. This inflammatory reaction has a variable effect on the reproductive strategy of the species studied. For example, this foreign body reaction can be localized within the uterus of rodents; and in farm animals it can have striking extrauterine effects. Thus, the action of IUDs in humans cannot be discerned from animals. In humans, copper ions released from Cu-IUDs enhance the inflammatory response and reach concentrations in the luminal fluids of the genital tract that are toxic for spermatozoa and embryos. In women using the IUD, the entire genital tract seems affected, at least in part, because of luminal transmission of the fluids that accumulates in the uterine lumen. This affects the function or viability of gametes, decreasing the rate of fertilization and lowering the chances of survival of any embryo that may be formed, even before it reaches the uterus. Studies on the recovery of eggs from women using IUDs and from women not using contraception show that embryos are formed in the tubes of IUD users at a much lower rate compared with nonusers. This is believed to be the major action of IUDs. Therefore, the common belief that the major mechanism of action of IUDs in women is through destruction of embryos in the uterus (i.e., abortion) is not supported by the available evidence. In Cu-IUD users, it is likely that few spermatozoa reach the distal segment of the fallopian tube, those that encounter an egg may be in poor condition. Thus, the few eggs that are fertilized have little chance for development and their possibility for survival in the altered tubal milieu become worse as they approach the uterine cavity.

Embryotoxicity of leukocyte extracts and its relationship to intrauterine contraception in humans

Twelve human uteri containing intrauterine contraceptive devices (IUDs) and ten uteri without IUDs were obtained at hysterectomy. Samples of fluid were collected from the uterine lumina by absorbing the fluid in small pieces of lens paper. In the samples of luminal fluid we measured the concentration of beta-galactosidase, an enzyme which is present in human neutrophilic leukocytes and whose concentration in luminal fluid should correlate with the local inflammatory response to the intrauterine foreign body. In the samples of fluid from IUD-bearing uteri, the concentration of beta-galactosidase was significantly (P less than 0.0005) greater than that in luminal fluid from control uteri, the averages of the two groups differing by 3.8 units. To determine whether a foreign-body response of this magnitude could have any effect on preimplantation embryos, we cultured mouse embryos from day 4 to day 7 of development in culture media to which extracts of human leukocytes were added. All mouse embryos were killed when the culture media contained enough leukocyte extract to give beta-galactosidase concentrations of 0.5 unit or higher. Thus mouse embryos were killed by leukocyte extracts whose beta-galactosidase concentrations were actually less than the concentration of this marker enzyme measured in IUD uterine fluid. This comparison indicates that the luminal fluid in IUD-bearing uteri contains leukocyte break-down products in sufficient concentration to be lethal for preimplantation embryos.

Effects of intrauterine devices on nuclear deoxyribonucleic acid metabolism in rabbit blastocysts: an autoradiographic study

A metabolic parameter, DNA synthesis, was measured in rabbit blastocysts exposed to Silastic intrauterine devices (IUDs) and compared with those without IUD exposure. Autoradiographic detection of 3H-thymidine uptake showed that the IUD-exposed blastocysts contained fewer labeled cells than their IUD-free equivalents. The depressed DNA synthesis may be caused by either a block in the cell cycle or a block in DNA synthesis itself. Either way, the result could be consistent with the observation that embryo deaths occur at all growth stages, preimplantation, during implantation, and postimplantation.

Neutrophils and the mechanism of IUD action in rats

Current research on the mechanism of action of the IUD has focused on a local, low-grade endometritis in preventing blastocystic implantation. With rabbit antisera to rat neutrophils, a neutropenic state was induced in rats having a silk suture in one uterine horn. Assay for nidation sites in the severely polymorphdepleted rats revealed no implantation sites in the IUD horn and an average of 5.8 sites in the control horn, suggesting that inflammation plays a relatively minor role, if any, in the mechanism of action of the IUD.