Vascular permeability to plasma proteins in uterine implantation and non-implantation sites (i.e. dye sites and non-dye sites) was assessed quantitatively by a method which accounts for steady-state volumes of distribution. Extracellular fluid volume and uterine blood flow were also determined. On both the evening of Day 5 and the morning of Day 6, vascular permeability to 125I-labelled human serum albumin, extracellular fluid volume and blood flow were significantly increased in implantation sites compared to non-implantation sites. Vascular permeability in implantation sites was increased significantly between Days 5 and 6, whereas that in non-implantation sites was unchanged. This increase in vascular permeability between Days 5 and 6 was not accompanied by further increases in extracellular fluid volume and blood flow. This result shows a dissociation between vascular permeability and extracellular fluid volume immediately after the onset of implantation and raises important questions as to whether the rat uterus undergoes a truly oedematous response at implantation as has been generally accepted.
Pregnant mice were injected 32 h post coitum (p.c.) with a monoclonal antibody against progesterone (5.7 or 9.5 nmol immunoglobulin G (IgG)) or 0.9% (w/v) NaCl (controls). Progesterone was injected starting on day 2, 3, 4 or 5 p.c. Progesterone reversed the antifertility effect of the lower dose of antibody when replacement began on day 2, 3 or 4, though the number of implantation sites was reduced when treatment started on day 3 or 4. By day 5 only one of six treated animals remained pregnant, showing that antibody action was reversible only up to day 4. At the higher dose of antibody, exogenous nidatory oestrogen was also required. Pseudopregnant mice were injected 32 h p.c. with this antibody (5.7 nmol IgG) or 0.9% NaCl (controls). At 16.00 h on day 4 p.c., oil was injected into the lumen of one uterine horn and the magnitude of the decidual cell reaction was assessed 72 h later. Injected horns of antibody-treated females did not respond to intraluminal oil, whereas those of control mice increased fivefold in weight. Steroid treatment after the induction stimulus did not promote decidual growth, indicating that passive immunization reduced endometrial sensitivity. The results show that in the event that antibody fails to arrest the development of all embryos, the absence of endometrial sensitization will preclude the initiation of implantation, unless progesterone is given within 48 h of antibody treatment.
Summary. The concept of a blood-tissue barrier defines the rates at which matter exchanges among the vascular and extravascular fluids of the tissue. The remarkably slow rates at which substances such as mannitol ( M , 182) enter uterine fluid from plasma demonstrate the existence of a blood-uterine lumen barrier. Available evidence indicates that the uterine microvascular endothelium and the uterine epithelium behave as lipoid layers interrupted by water-filled channels. Furthermore, both cell layers appear to select actively certain substances over others for exchange with opposing extracellular fluids. In contrast to these similarities, the uterine epithelium and endothelium differ considerably with regard to restrictiveness. For most substances the primary rate-limiting boundary between blood and the uterine lumen is the epithelium. The extracellular fluid compartments of the lumen and endometrium are also influenced by the internalization and release of materials into and out of intracellular compartments including those of the stromal and migratory cells of the endometrium, the epithelium and the developing conceptus. Considerable evidence suggests that the luminal milieu of the developing embryo is created and maintained by the transport and permeability properties o r the blood-uterine lumen barrier in conjunction with the cellular activities of the endometrium and embryo. This milieu probably fulfils the informational and nutritional needs of the developing embryo.
A scoring scheme was devised to characterize visually the morphological differentiation of whole-mount, unfixed mouse blastocysts. Embryos were recovered from groups of intact mice (implanting embryos) and mice ovariectomized on Day 3 of pregnancy (implantation-delayed embryos) every 3 h from 18:00 h on Day 4 until 12:00 h on Day 5. Blastocyst differentiation was assessed according to the presence of a zona pellucida, the appearance of the outer margin of trophectoderm cells, the visibility of the blastocoele and the relative size of the inner cell mass. The results obtained indicate that, during this period, implanting and implantation-delayed mouse blastocysts lose the zona as well as exhibit rounded trophectoderm cells, an enlarged inner cell mass and an increasing opacity of the blastocoele. In contrast, the trophectoderm cells of implanting blastocysts only exhibit extensive cytoplasmic projections, probably due to remodelling of the intracellular cytoskeleton. Growth of the inner cell mass appeared to precede the other morphological changes in the majority of blastocysts, and thus might be a prerequisite for further differentiation. The rate of blastocyst differentiation and the survival of embryos were adversely affected by the condition of delayed implantation, induced by ovariectomy. This study suggests that the appearance of cytoplasmic projections from trophectoderm cells is central to the control of blastocyst implantation.
To investigate the influence of molecular size on the abilities of polar, nonelectrolytic substances to diffuse passively across the blood-uterine lumen barrier, the abilities of [3H] mannitol, [3H] sucrose and [3H] inulin (mol. wt. 182, 342 and 5200, respectively) to enter uterine luminal fluid from blood were compared in immature, ovariectomized rats implanted for 3 days with Silastic capsules containing estradiol. Relatively constant serum radioactivity concentrations were achieved for the period of 1-4 h after intravenous injection of the test substances by tightly ligating the renal pedicles of all animals prior to injection. Although uterine fluid radioactivity concentrations for [3H] inulin increased significantly between 1 and 4 h after injection, those for [3H] sucrose and [3H] mannitol did not change significantly with time, thus preventing calculation of conventional permeability indices. Therefore, the ratios of uterine fluid to serum radioactivity concentrations 2 h after intravenous injection of the test substances into animals with ligated renal pedicles were determined; the ratios (means +/- SEM) for [3H] mannitol, [3H] sucrose and [3H]-inulin were 0.11 +/- 0.015, 0.038 +/- 0.011 and 0.037 +/- 0.012, respectively. As indicated by these ratios, the rate of transfer into the uterine lumen of [3H] mannitol relative to that of [3H] sucrose was markedly greater than predicted by the ratio of their respective aqueous diffusion coefficients at body temperature. This disproportionality suggested that diffusion across the blood-uterine lumen barrier by some substances is governed by molecular sieving (sterically restricted diffusion) and therefore that this barrier is selectively permeable to these substances on the basis of molecular size.(ABSTRACT TRUNCATED AT 250 WORDS)
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