Dispersal of rat uterine mast cells and their functional response to an embryo-derived histamine releasing factor: a possible model for embryo implantation

Increased appearance of inducible nitric oxide synthase in the uterus and embryo at implantation

The aim of this study was to investigate the presence of iNOS in the murine uterus and embryo at implantation. Western blot analysis showed the presence of a 130-kDa band with strong reactivity to anti-iNOS antibody in the pre- and peri-implantation stage uteri. This band was faint in the postimplantation uteri. Immunocytochemical studies showed a heavy localization of iNOS specifically on the apical cells of the uterine endometrium in the pre- and peri-implantation stages. But the postimplantation uteri showed resorbed endometrium showing weaker expression of iNOS. The iNOS was induced by estrogen and the induction was intensified when progesterone was given along with estrogen. This truly mimics the in vivo situation since implantation in mice occurs when an estrogen surge occurs on a background of progesterone. The embryos too express iNOS at the peri-implantation stage. We suggest that iNOS expressed at peri-implantation would lead to enhanced NO production, which could act as a vasodilator and an angiogenic mediator. These effects could promote the attachment of the blastocyst to the uterus.

Inhibitory effect of neuraminidase on SP-induced histamine release and TNF-alpha mRNA in rat mast cells: evidence of a receptor-independent mechanism

The neuropeptide substance P (SP) is a mediator of neuro-inflammation and can play a role by induction of histamine release (HR) and TNF-alpha. However, its effect on the heterogeneous response of mast cells (MC) has not been completely studied. We have established that the SR can induce 25% of HR in highly purified rat uterine MC at diestrous but not at proestrous phases of the reproductive cycle and 88% of HR in peritoneal mast cells (PMC). We also found 2.2 fold increase in TNF-alpha mRNA at diestrous, in SP stimulated uterine MC versus control and 2.7 fold increase in PMC; RT and competitive PCR were used to amplify the TNF-alpha mRNA. We have thereafter investigated the mechanism whereby the binding of SP to sialic acid on the MC membrane, could trigger secretion of histamine and induction of TNF-alpha mRNA. The neuraminidase pretreatment (0.1 U/ml) inhibited SP-stimulated HR from either uterine MC and PMC (98% and 50%, respectively) and totally inhibited SP-stimulated TNF-alpha mRNA levels. The neuraminidase effect was not toxic, since it was not observed in IgE mediated HR and TNF-alpha mRNA levels. In conclusion, the inhibitory effect of the neuraminidase on the SP-mediated increase of histamine and TNF-alpha mRNA, suggests that the SP-sialic acid interaction could have a role in the MC heterogeneous response.

Changes in vascular permeability and deciduoma formation during the peri-implantation period of the rat in response to exogenous gonadotropins

BACKGROUND

Permeability of thin-walled vessels of the endometrium could be a prerequisite for deciduoma formation. Exogenous gonadotropins alter endometrial morphology and inhibit vascular permeability on the day of implantation. The aim of this study was to investigate the effect of exogenous gonadotropins on vascular permeability in the peri-implantation period and relate this to deciduoma formation.

METHODS

Female rats were hyperstimulated with follicle-stimulating hormone and human chorionic gonadotropin prior to mating. Control animals were not injected. Endometrial tissue was collected at 4.5, 5.5, and 6.5 days after mating. Tissue was processed for electron microscopy.

RESULTS

The presence of thin-walled fenestrated vessels and decidualised stromal cells were found in all control groups. With the exception of one fenestration, which occurred in a vessel from one hyperstimulated animal on 5.5 days of pregnancy, no fenestrations were found in the vessels of hyperstimulated animals. Decidualisation of stromal cells did not occur in these animals.

CONCLUSION

Hyperstimulation with exogenous gonadotropins inhibits vascular permeability and subsequent decidualisation. Implantation thus fails to occur.

Cytological aspects of vascular invasion by the trophoblast of Calomys callosus in hepatic tissues

Ectoplacental cones isolated from embryos on the seventh day of pregnancy were transplanted beneath the hepatic capsule of recipient adult animals to document the morphological patterns of vascular invasion by the trophoblast in the absence of the maternal environment and the influence of its peculiar vasculature. Females, and females and males of Calomys callosus, a cricetid rodent, were used, respectively, as embryo donors and recipient animals. Three to 5 days later, the grafted regions were excised and processed for light and electron microscopy. Invasion of the liver parenchyma by the trophoblast progressed along the vascular beds, associated with gradual phagocytosis of hepatic cells, greatly favoring the morphological characterization of invasive steps exhibited by the trophoblast to access the different kinds of vessels, to trespass the various vascular components and the different levels of the surrounding hepatic parenchyma. It is possible that either in utero during the establishment of embryomaternal circulation in early pregnancy or ex utero under experimental conditions, the trophoblast exhibits similar vascular invasion behavior. In view of this, our findings may contribute to a better understanding of trophoblast cell migration to the maternal blood supply as well as the role of the trophoblast in the establishment of the placental circulation during pregnancy.

Effect of substance P on uterine mast cell cytokine release during the reproductive cycle

There is increasing evidence that neuropeptides, steroid hormones and inflammatory cytokines influence the immune response during the reproductive cycle. In the present study, we focus on the effects of neuropeptide Substance P (SP) during the pre-implantation stage of embryo development (day 4 of pregnancy), at pro-estrus and di-estrus (two phases with different hormonal states). We found heterogeneous responses to SP and anti-IgE by the rat uterine mast cells (MCs), as detected by ELISA. In fact, MCs purified from uteri on day 4 of pregnancy released histamine, granulocyte macrophage-colony stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha) in response to anti-IgE, but not to SP. When pre-incubated with SP, the release to anti-IgE was significantly enhanced compared to anti-IgE alone. Exposure of SP to antibodies to SP, prior to pre-incubation with MCs, negated the SP effect on IgE-mediated release. At the pro-estrus phase SP showed similar behavior as on day 4 of pregnancy, whereas at the di-estrus phase SP alone was capable of inducing release of histamine and cytokines from purified uterine MCs. Moreover, non-quantitative RT-PCR analysis of the TNF-alpha mRNA level suggested an SP stimulation at the di-estrus phase, but neither on day 4 of pregnancy nor at the pro-estrus phase. Taken together, these data strongly suggest that SP can modulate IgE-mediated uterine MC release of histamine and inflammatory cytokines in different ways, depending on the phase of the reproductive cycle.

Initial vascularisation in the pig placenta: I. Demonstration of nonglandular areas by histology and corrosion casts

The vascular interrelationship of the well-established porcine placenta has previously been described from vascular casts and histology, but not its developmental stages. This study was performed using the same methods on 17 sows of well-known stages of gestation ranging from 9 1/2 to 43 days post coitum (p.c.). At the precontact stage, days 9 1/2 to 12 1/2 p.c., the subepithelial capillaries formed a wide open meshwork of variable diameter, 3-14 microns, without any difference between meso- and antimesometrial side. At the early contact and adhesion stages (days 13 to 18 p.c.), the first increase in vasculature was seen at the mesometrial side close to the embryonic disc of the very long blastocyst at day 15 p.c., 2 days after the first contact between trophoblast and maternal epithelium was seen. At day 18 p.c., the areas with dense capillaries increased markedly at the mesometrial side with the same parallel organization as seen at day 15 p.c., whereas the antimesometrial side still had a relative loose appearance comparable to the previous stages. At the early placental stages (days 20 1/2 to 23 p.c.), the capillary bed formed smooth folds, which in some areas at day 20 1/2 days developed into smaller folds or prerugae. Here the capillaries changed to convoluted forms with slightly bulbous dilations measuring about 30-35 microns in diameter. This developmental progress became more elaborate at day 23: capillaries of the low ridges of prerugae formed irregular dilations up to 50 microns in some areas. At this stage the parallel arrangement of the capillary meshwork characteristic of the previous stage was not longer discernable. By days 32-43 p.c., an increase in microscopic folding was present, and the maternal arterioles could be traced to the top of the ridges, creating the characteristic vascular architecture needed for an efficient exchange of oxygen, carbon dioxide, and nutrients of the basically developed porcine placenta.

Mast cell heterogeneity in man: unique functional properties of skin mast cells in response to a range of polycationic stimuli

Human mast cell heterogeneity was assessed by histochemical and detailed functional criteria using mast cells isolated from foreskin, uterine myometrium and lung parenchyma. The skin mast cells were histochemically distinct from their counterparts in the other two tissues by being predominantly insensitive to blockage of dye-binding following formalin fixation (ca. 80%). Functionally, a wide range of structurally diverse polycationic compounds induced selective histamine release from the skin mast cells (ca. 10% at top concentrations) although these cells were less responsive to immunological ligands and calcium ionophores when compared with the uterine and lung cells. The basic compounds, polyarginine and histone, proved to be more generalised histamine liberators as compared with their structural analogues, polylysine and protamine sulphate, probably by virtue of their high content of arginine residues and hydrophobic nature (histone). Studies with the anaphylatoxin, C3a, and its analogues 21R and C3ades Arg on skin mast cells emphasized the importance of basic amino acids for histamine-liberating peptides. Skin mast cells also proved more susceptible than their uterine counterparts to lysis by the detergents, Triton X-100 and Tween 20, suggesting that fundamental differences in membrane structure and/or fluidity might account for functional heterogeneity within the human mast cell population.

The human skin mast cell: a comparison with the human lung cell and a novel mast cell type, the uterine mast cell

The functional and histochemical properties of isolated mast cells from human skin, uterine myometrium and lung parenchyma were compared. The skin cell showed a marked difference in responsiveness to both secretagogues and anti-allergic compounds when compared to mast cells from the uterus and lung. The latter cell types responded more strongly to immunologically-directed ligands and calcium ionophores than the skin cell. However, the skin cell released histamine in response to a wide variety of polycationic compounds whilst the lung and uterine cells were essentially refractory to these agents. The antiallergic drugs, disodium cromoglycate (DSCG) and nedocromil sodium, were weakly inhibitory against the skin cell but were in contrast more effective against the lung and uterine cells.

Sites of endometrial vascular leakage during implantation in the rabbit

Vascular labelling with carbon suspension was used to identify endometrial vessels demonstrating macromolecular leakage at implantation sites in the rabbit. Extravasation was seen first in venous components of the deep endometrial stroma on the mesometrial aspect of implantation sites. Carbon labelling was apparent in such vessels at 7 d, 0 hr post coitum, (p.c.), and was attributed to gap formation between endothelial cells. Later in the implantation process, leakage was seen as microextravasations of carbon in the lateral and antimesometrial walls of implantation chambers. Here, penetration of vessels by trophoblast was apparent and membranous processes from the trophoblast projected into vessel lumina. Extravasated material (carbon, platelets) was localized to a labyrinthine system of membranes within the trophoblast, and a potential role for the labyrinth in handling of ingested plasma constituents is discussed. A similar process of trophoblastic penetration of vessels occurred on the mesometrial aspect of implantation sites several hours later. Systemic administration of the anti-inflammatory agent indomethacin blocked vascular leakage due to endothelial gap formation but had little or no effect on trophoblast knob penetration of vessels. This observation may explain the results of previous studies in which treatment with anti-inflammatory agents reduced, but could not inhibit completely, the vascular permeability changes at implantation sites.