Post-implantation development of demi-embryos and induction of decidual cell reaction in mice

Mouse demi-embryos that developed from bisected morulae were transferred to recipients. The eu-blastocysts (distinct inner cell mass and well-developed trophectoderm) contained cells equal to 51% of the controls that developed from zona-free morulae. The rate of decidual cell reaction induced by the eu-blastocysts was not significantly different from that of the controls, but the size of the deciduum containing the egg cylinder was significantly smaller on Day 5.5 of pregnancy (P < 0.001). A significant increase in embryonic loss was observed from Day 7.5 to Day 9.5 in the eu-blastocysts (P < 0.05), while the controls exhibited no significant difference. Although the embryos from the eu-blastocysts showed retardation of developmental stages and decreased size, they attained normal stages and size regulation up to 90% of that of the control on Day 10.5. The pseudo-blastocysts (poorly developed inner cell mass enclosed by trophectoderm) contained cells equal to 25% of those of the controls and showed less than a 10% developmental rate to the egg cylinder stage. The trophectodermal vesicles (no enclosed cells) and nonintegrated forms (disorganized clusters of cells) contained cells less than 18% of those of the controls. They showed lower rates of decidual cell reaction than those in the controls (P < 0.05), and no egg cylinder was found in the deciduum. The results indicate that a severe decrease in the number of embryonic cells affects the regulation of embryonic development and decidual cell reaction in the uterus.     

Tissue spaces during development and regression of the decidual cell reaction in ovariectomized, steroid-treated mice

Changes in the extracellular and blood spaces of the uterus were assessed from the distribution volumes of 51Cr-EDTA and 51Cr-labelled red blood cells during the development and regression of the artificially induced decidual cell reaction in ovariectomized, steroid-treated mice. The normally high values for uterine extracellular space (0.35-0.40 microliter/mg) fell to less than 0.20 microliter/mg in association with decidual growth. Uterine blood space increased from around 0.02 microliter/mg to 0.03-0.05 microliter/mg with decidual development. Induction of decidual regression by removal of s.c. progesterone implants caused a rapid decline in tissue blood volume to reach control values (0.01-0.02 microliter/mg) within 24 h and preceded any reduction in uterine weight. Uterine vascular permeability, as determined from the tissue accumulation of 125I-labelled human serum albumin, fell with a similar time course. Tissue extracellular space returned to the higher control values within 48 h of initiating decidual regression.     

Uterine blood flow during the development and regression of the decidual cell reaction in ovariectomized, steroid-treated mice

Uterine blood flow was assessed in mice by measuring organ uptake of intravenously injected [14C]butanol. In ovariectomized mice, injection of 100 ng oestradiol-17 beta increased blood flow 5-fold over that of untreated controls. The injection of oestradiol-17 beta in progesterone-treated mice also increased uterine blood flow at the time of maximal sensitivity to a decidual stimulus, but not 4 days later. Absolute values of blood flow increased during development of the decidual cell reaction in proportion to the increase in uterine weight, reaching maximal values 96 h after decidual induction. When progesterone injections were stopped 72 h after decidual induction, a rapid decrease in absolute and relative blood flow values preceded the decrease in uterine weight. This decrease in uterine blood flow occurred within 12 h of removing a subcutaneous implant containing progesterone. These results are consistent with the view that increased uterine blood flow during decidual development may be necessary to support the rapid increase in uterine weight at implantation and the subsequent decrease in both relative and absolute uterine blood flow on withdrawal of progesterone may promote decidual regression in the mouse.     

The action of high doses of oestradiol on implantation and decidual reaction in the rat

The action of high doses of oestradiol on ovum implantation and decidual reaction was studied in pseudo-pregnant rats. It is shown that anomalies of ovum implantation take place after the injection of 10 μg of oestradiol on the 4th day of pregnancy, in that the decidual reaction is inhibited as demonstrated by ponderal evolution, lower ³H uridine uptake, ultrastructural features and the ploidy level of stromal cell nuclei.     

6-Keto-prostaglandin E1 and the decidual cell reaction in rats

Although there is considerable evidence that prostaglandins (PGs) are involved in the decidual cell reaction in rats, which PGs are involved is uncertain. In the present study, we investigated the possibility that 6-keto-PGE1 is involved. To determine its ability to induce decidualization, 6-keto-PGE1 was infused unilaterally from Alzet osmotic minipumps into the uterine lumen of ovariectomized rats treated with estrogen and progesterone to sensitize their uteri for the decidual cell reaction. To reduce endogenous PG production, indomethacin was injected 2-3 h prior to pump insertion and was included in the vehicle for PG infusion. As determined by uterine weights 5 days after pump insertion, 6-keto-PGE1 and PGE2 produced decidualization which was equivalent. As indicated by a dose-response study, 6-keto-PGE1 and PGE2 did not differ in their ability to bring about decidualization. To determine if a deciduogenic stimulus resulted in increased uterine production of 6-keto-PGE1, as assessed by uterine concentrations, 6-keto-PGE1 and PGE concentrations in the uterus were determined after the unilateral intrauterine injection of 100 microliters sesame oil. There were no significant differences between stimulated and non-stimulated horns in 6-keto-PGE1 concentrations, whereas the concentrations of PGE2 were elevated in the stimulated horns. These data indicate that while both exogenous 6-keto-PGE1 and PGE2 induce decidualization, only uterine PGE concentrations are elevated by deciduogenic stimuli. Thus it is unlikely that 6-keto-PGE1 plays a role in decidualization.     

A study of the early morphological changes initiated in the uterine luminal epithelium by substances (oil and carrageenan) which induce the decidual cell reaction in mice

Oil, carrageenan or saline were injected into the uteri of ovariectomized mice treated with hormones on schedules which would sensitize, partly sensitize or not sensitize the uterus to an intraluminal decidual stimulus. The uterine epithelium was examined histologically at various times over the succeeding 5 h. Saline did not produce any morphological change whereas almost immediately after the injection of oil or carrageenan epithelial cell death was apparent in the uterus, regardless of hormone treatment. Within 45 min the dead cells had been removed and the epithelium was re-established. Oil droplets were still present in the uterus after 5 h and these were able to stimulate a decidual reaction in partly sensitized animals when oestrogen was administered 18-44 h after the oil instillation, well after the re-establishment of the epithelium. It is suggested that the early transient cell death in the uterine epithelium is not responsible for triggering the decidual reaction but that it is the contact of the oil droplet with an intact epithelium which triggers the response when the hormonal conditions so allow.     

Secretion of plasminogen activator by cultured rat endometrial stromal cells from uteri differentially sensitized for the decidual cell reaction

Endometrial stromal cells from rat uteri differentially sensitized for the decidual cell reaction in vivo and which undergo differing degrees of decidualization in vitro were cultured and plasminogen activator (PA) in the medium determined. The cells were obtained by enzymatic dispersion from the uteri of ovariectomized, steroid-treated rats at the equivalent of day 4, 5, or 6 of pseudopregnancy or on day 5 from rats treated on day 4 with 0, 0.3, or 1.0 μg estradiol (low, intermediate, or high dose of estradiol, respectively) and cultured for 24, 48, or 72 hr. For cells from day 4, 5, and 6 uteri cultured under control conditions, PA activity in the medium was greatest for day 5 cells, which were from uteri maximally sensitized for decidualization both in vivo and in vitro. By contrast, for cells from low-, intermediate-, and high-estradiol uteri, PA activity in the medium was greatest for the high-estradiol cells; these cells do not undergo decidualization in vivo or in vitro to the same extent as intermediate-estradiol cells. Indomethacin, an inhibitor of prostaglandin (PG) synthesis, reduced PGE₂ accumulation to nondetectable amounts and for most cultures decreased PA activity in the medium, suggesting that endogenous PG production regulated in part PA secretion under control conditions. The addition of PGE₂ with indomethacin increased PA activities above those under control conditions, but activities were still lower for day 4 and 6 cells compared with day 5 cells, and for low- and intermediate-estradiol cells compared with high-estradiol cells. This indicates that the differences in PA secretion are not explainable by differences in PGE₂ production. Northern blot analysis of RNA from cells cultured for 72 hr under control conditions did not reveal significant differences in steady-state concentrations of mRNA for urokinase-type PA or plasminogen activator inhibitor 1, but those for tissue-type PA were lower in day 6 cells compared with day 4 and 5 cells. It is concluded that PA activity secreted by the cultured endometrial stromal cells, although controlled in part by the endocrine milieu to which they were exposed prior to culture, does not simulate decidualization in vitro and, therefore, that PA activity is not a marker for decidualization in vitro. Mol. Reprod. Dev. 49:268–276, 1998. © 1998 Wiley-Liss, Inc.     

Role of platelet-activating factor (PAF) in the initiation of the decidual reaction in the rat

Injection of PAF into the left uterine horn induced a dose-dependent decidua-like reaction in the pseudopregnant rat. This reaction was maximal when PAF was injected at Day 5 of pseudopregnancy and was blocked by the specific PAF antagonist, BN 52021. BN 52021 did not interfere with the decidual reaction induced by prostaglandin E-2 or insertion of a cotton thread in the uterine horn. In contrast, a decidua-like reaction was not evoked by the inactive lyso-PAF, demonstrating the specificity of the action of PAF. The decidua-like reaction induced by PAF involves the generation of cyclooxygenase metabolites of arachidonic acid since it was inhibited by indomethacin. The histological alterations induced by PAF were similar to those observed after embryo implantation, strengthening the postulate for a role of the autacoid in the early stages of pregnancy.     

Effects of ethanol on the decidual cell reaction in rats.

The effects of ethanol on uterine sensitivity to induction of decidualization and deciduoma growth were determined. Rats were ovariectomized, given an oestrogen-progesterone regimen to optimize induction and growth of deciduoma and randomly assigned to one of three ethanol treatment groups: (i) days 1-4 (pre-induction/period of sensitivity), (ii) days 5-9 (post-induction/period of growth), (iii) days 1-9 (periods of sensitivity and growth); or to a control group not treated with ethanol (pair-fed to treated groups). Ethanol (0, 1, 2, or 4 g kg-1) diluted in water was administered by stomach tube on the days prescribed. Decidualization was induced in one uterine horn by intraluminal injection of sodium phosphate buffer. Uterine sensitivity and decidual growth were assessed as cornu weight. Blood alcohol concentrations were measured by gas chromatography. Alcohol treatment reduced uterine sensitivity, but increased deciduoma growth. Blood alcohol concentrations rose to 133 mg% at 30 min, remained high for 90 min and declined to 82 mg% at 120 min. Thus, blood alcohol concentrations sufficient to induce mild intoxication in humans suppressed uterine sensitivity to decidualization and enhanced deciduoma growth in rats. As all ovarian steroid hormone support was exogenous, the effects of ethanol on deciduoma induction and growth were not due to alterations in the hypothalamic-pituitary-ovarian axis.