Ultrastructure of mouse uterine surface epithelium under different estrogenic influences

Local and systemic factors and implantation: what is the evidence?

Significant progress has been made in the understanding of embryonic competence and endometrial receptivity since the inception of assisted reproductive technology. The endometrium is a highly dynamic tissue that plays a crucial role in the establishment and maintenance of normal pregnancy. In response to steroid sex hormones, the endometrium undergoes marked changes during the menstrual cycle that are critical for acceptance of the nascent embryo. There is also a wide body of literature on systemic factors that impact assisted reproductive technology outcomes. Patient prognosis is impacted by an array of factors that tip the scales in her favor or against success. Recognizing the local and systemic factors will allow clinicians to better understand and optimize the maternal environment at the time of implantation. This review will address the current literature on endometrial and systemic factors related to impaired implantation and highlight recent advances in this area of reproductive medicine.

Hemoglobin absorption by the cells of the proximal convoluted tubule in mouse kidney

The formation of protein absorption droplets in the cells of the proximal convolution was studied in mouse kidney. Ox hemoglobin was administered intraperitoneally and kidney specimens were collected at intervals of 30 minutes to 4 days after injection. In the lumen of the nephron, hemoglobin was concentrated to an opaque mass whose relations with the brush border and the epithelium could be easily followed. It was found that hemoglobin passes through the brush border in between the microvilli, enters the channels of tubular invaginations at the bases of the brush border, and is transported in bulk into vacuoles in the intermediate cell zone. These vacuoles increase in size and are transformed through further concentration into dense absorption droplets. Using the opaque hemoglobin content of the nephron as a tracer, functional continuity of the system of the tubular invaginations with the lumen on one side and the vacuoles on the other was demonstrated. Mitochondria lie closely apposed to vacuoles and droplets, but are not primarily involved in droplet formation. 15 hours after injection and later, ferritin and systems of layered membranes become visible in the droplets as their density decreases. These membranes are interpreted as lipoprotein membranes; similar membranes are found in the lumen of the tubuli. It is suggested that phospholipids enter into the vacuoles together with hemoglobin from the tubular lumen and form membrane systems of lipoproteins in the droplets. At 3 to 4 days the droplets contain aggregates of ferritin, and the iron reaction becomes positive in the tubule cells. No significant changes were found in the Golgi apparatus or in the microbodies during hemoglobin absorption. At all time points investigated, the terminal bars seal the intercellular spaces against penetration by hemoglobin in the proximal and distal convolutions and in the collecting ducts.

AN ELECTRON MICROSCOPE STUDY OF THE GLAND CELLS OF THE MINK ENDOMETRIUM

Portions of mink endometrium in delayed implantation, early postimplantation, and pseudo pregnancy were fixed in buffered osmium tetroxide with sucrose, or potassium permanganate. After rapid dehydration the portions of endometrium were embedded in either methacrylate or epoxy resin. Examination of the cells from the body of the glands of the endometrium of delayed implantation revealed the presence of prominent terminal bars, numerous secretion granules, and membrane discs in the apical region of the cell. In the supranuclear and infranuclear regions, mildly dilated cisternae of the endoplasmic reticulum were present, and in many cells unusually large mitochondria were seen. Numerous changes were noted in the gland cells of the post implantation stage. The endoplasmic reticulum in the basal region was extensively dilated, and the nuclei were situated more centrally. Giant mitochondria were no longer present. The large secretion granules were not present, but smaller granules were seen, especially in the Golgi region. Some of the Golgi cisternae were dilated and the pattern of parallel membranes was consequently less distinct. It is suggested that gland cells in the postimplantation and pseudopregnancy stages exhibit evidence of greater secretory activity than those in the delayed implantation stage.

Induction of nucleolar changes in rat luminal cells by single injection or low-dose infusion of estradiol

The nucleolar area of rat uterine luminal epithelial cells was measured for 41 h after beginning either of two dosage regimens of estradiol (E2): a single injection of 1.0 microgram E2 or a continuous infusion of E2 at a rate of 1.0 microgram/24 h. In response to a single injection of E2, mean nucleolar area was significantly elevated above control levels by 10 h. Nucleolar morphology showed slight changes, but the fibrillar component was always associated with 2-3 fibrillar centers by 10 h. In response to a continuous infusion of E2, mean nucleolar area was elevated by 10 h, reached a maximum by 18 h, and remained relatively constant thereafter. Nucleolar morphology showed significant changes by 10 h; the fibrillar component was commercially denser. Bivariate histograms of nuclear versus nucleolar areas showed a bimodal distribution after both injection and infusion, suggesting that two size classes of nuclei existed after estrogen stimulation. The results suggest that: 1) a continuous infusion of E2 at a rate of 1.0 microgram/24 h was more effective in inducing larger increases in nucleolar area and transcription than a single injection of 1.0 microgram E2 at time 0; 2) using analysis of nuclear and nucleolar areas two subpopulations of cells were identified; and 3) continuous infusion of E2 produced a steady state of ribosome production and cytoplasmic transport by 18 h.

Rat luminal cell nuclear area changes correlated with uterine growth responses induced by a low dose infusion or injection of estradiol-17 beta

Rat uterine luminal epithelial cells (LEC) responded differently when exposed to an injection of 1.0 microgram estradiol-17 beta (E2) compared to a continuous infusion of E2 at the rate of 1.0 microgram/24 hours. After injection or beginning infusion, LEC mean nuclear area significantly decreased by 4 h, then increased thereafter. After injection, nuclear area distributions were determined at each time point. The percentage of large nuclei (greater than 40 mu 2) decreased by 4h postinjection and remained a relatively small proportion of the population, while the percentage of nuclei of 20-30 mu 2 areas increased throughout the experiment. During infusion, the percentage of large nuclei decreased by 4h after pump implantation, then increased. Only infusion induced sustained, increased uterine protein content, DNA synthesis and ornithine decarboxylase activity. This study suggests that E2 treatment modality induces differences in nuclear size in target cells as well as in biochemical parameters.

Ultrastructural effects of estrogen replacement on postmenopausal endometrium

Endometrial adenocarcinoma occurs almost exclusively in postmenopausal women, and excessive or unopposed estrogen stimulation is suspect as a causative factor in its pathogenesis. Furthermore, the incidence of endometrial adenocarcinoma has increased in women undergoing estrogen replacement therapy. In the present study, the cellular response of premenopausal and postmenopausal endometrium to estrogenic stimulation was compared with endometrial adenocarcinoma by the electron microscope. Tissues were obtained at hysterectomy, endometrial biopsy, or endometrial curettage and were processed routinely for light and electron microscopy. Ultrastructurally the endometrium from postmenopausal patients undergoing estrogen replacement therapy was similar to normal cyclic endometrium in the late proliferative phase. At least three features of the estrogen-treated postmenopausal tissue resembled those observed in adenocarcinoma of the endometrium: accumulation of lipid droplets, irregular nuclei, and perinuclear whorls of microfibrils.

Estrogen and antagonist-induced changes in endometrial topography of immature and cycling rats

The topographical changes of the luminal surface of the endometrium of immature and ovariectomized rats treated with estrogen, antagonists to estrogen, and progesterone. and during various stages of the estrous cycle and in pregnancy were examined by scanning electron microscopy. Massive increases in numbers and length of endometrial cell microvilli were observed at estrus, after injection of estradiol-17beta, diethylstilbestrol, estrogen plus progesterone. or the inhibitor C1628 to immature and ovariectomized rats. Withdrawal of the estrogen stimulus results in diminution of microvilli, producing a state identical to diestrus, during pregnancy, and after injection of progesterone, The estrogen antagonist appears to have both estrogenic and progestogenic properties, stimulating endometrial cell hypertrophy, secretion of protein, and production of numerous apical microvilli.