Embryo implantation remains superficial (epithelio-chorial type) in most marsupials including the Macropodidae, but does involve formation of specialized contact zones of the trophoblast with the uterine epithelium. Since in eutherian mammals proteinases appear to play a central role in implantation-initiation mechanisms, a systematic histochemical investigation of proteinase patterns as related to implantation was performed in the tammar wallaby, Macropus eugenii (Macropodidae). Tammar uteri with embryos were collected at diapause and at days 7, 17, 18, 19, 20, 21 and 26 of the 27-day gestational period. Proteinase patterns were studied using a sensitive histochemical gelatin-substrate-film test previously optimized for the detection of trophoblast-dependent proteinase (blastolemmase) in the rabbit. Proteinase patterns were correlated with light-microscopical morphology of the processes of shedding of the extracellular embryo coverings (shell membrane) and attachment of the trophoblast to the uterine epithelium. At acid pH values an intracellular proteinase is detected in yolk sac endoderm and trophoblast as well as in endometrial glands and certain stromal cells. This enzyme is proposed to be a cathepsin indicating high catabolic activity connected particularly with protein transport from the endometrium into the yolk sac. Peak activity is found in the avascular (bilaminar) yolk sac at the phase when contact with the endometrium is being established. A particularly interesting proteinase active at alkaline pH values is detected in the trophoblast-endoderm complex. This enzyme appears to be extruded into the interface between trophoblast and uterine epithelium where it shows maximal activity for only approximately one day, around day (18-)19, exclusively in the bilaminar (avascular) yolk sac. The activity is correlated with the process of shedding of the extracellular embryo coverings (shell membrane) and of subsequent attachment of the trophoblast to the uterine epithelium, in the bilaminar but not the trilaminar (vascular) yolk-sac region. This is the first report on an extracellular (alkaline) proteinase activity possibly serving a specific function in embryo implantation in a marsupial.
Daily blood samples were taken for progesterone (P) and estradiol (E2) measurements from women who showed a platelet response consistent with the presence of viable embryos after in vitro fertilization and embryo transfer procedures. A comparison of steroid levels between those women who became pregnant and those who did not revealed the following: at and after the time of transfer, women who failed to become pregnant had significantly higher E2 levels and a lower ratio of P/E2 than women who became pregnant. The P/E2 ratio was a better predictor of implantation failure than was the absolute level of either hormone. Experiments were done in mice to test the hypothesis that P could protect implantation of the embryo against the inhibitory effects of high E2. In mice, implantation was inhibited by relatively high levels of E2. This effect was overcome by concomitant administration of P. There was a significant dose-response-related interaction of P with the E2.
The uptake of pyruvate and glucose by single, cultured mouse embryos has been measured non-invasively throughout the pre-implantation period. The embryos, derived from CBA x C57F1 females and F1 males were removed from the oviducts on day 1 or day 2 following mating, and cultured to the blastocyst stage in M16 medium. Each day they were removed from culture and incubated in 20 nl medium M2 for 3 h. Serial approximately 0.5-nl samples were analysed for pyruvate and glucose by an ultramicrofluorescence technique. Pyruvate uptake exceeded that of glucose until the 8-cell/morula stage, when glucose consumption increased dramatically. The morphological development and patterns of nutrient uptake by embryos removed on day 2 resembled more closely those of freshly collected embryos than of embryos removed on day 1. These methods will enable the biochemistry of early embryos to be monitored non-invasively prior to transferring them into the uterus of recipient females.
The implantation rates and subsequent pregnancy rates in in vitro fertilization (IVF) programs are lower than those currently seen in the normal fertile population. During IVF treatment regimens, intercourse is not allowed and artificial insemination is normally excluded. This trial, involving the deposition of semen in the high vaginal area, was undertaken for evaluation of the influence of sperm in the reproductive tract on subsequent implantation rates. The results show that the implantation rate, as assessed by a rise in the human chorionic gonadotropin levels in inseminated patients, was 53%, compared with 23% in the control group. The implantation rate of 54% in the group who had tubal occlusion or no fallopian tubes was not significantly different from the implantation rate of 50% in the group with patent tubes, which suggests that the site of sperm influence was on the endometrium and that the absence of the fallopian tube has no significant effect upon this influence.
Four hatched human blastocysts obtained after in-vitro fertilization and development were placed on monolayer cell cultures of human endometrial epithelium, and subsequently examined by transmission electron microscopy. All four blastocysts became adherent to the monolayer and three implanted and exhibited outgrowth of their trophoblastic cells. During implantation the blastocysts differentiated into mural and polar trophoblastic cells, and embryonic cells including endodermal cells. The endometrial cells were displaced and stacked into a multilayer at the periphery of the implantation sites, allowing the trophoblastic cells to come in contact with the culture dish. The endometrial cells displayed local exo- or endo-cytosis where they contacted the trophoblastic cells. The trophoblastic cells were not observed to be phagocytosing endometrial cells. These observations suggest that human blastocysts portray an intrusive type of implantation during the initial stages.