Comparative enzyme histochemistry of the early and term rat decidua with special attention to decidual regression

Mode of cell death in the rat metrial gland during peripartum regression

In the rodent uterus, the metrial gland develops during midpregnancy and undergoes regression prior to parturation. The involution of the gland is reported to be accompanied by the loss of gland cells due to their death in situ. Cell death has been classified by using morphological criteria into two types: necrosis and apoptosis. To study the mechanism involved in the peripartum regression of the rat metrial gland, we examined the mode of cell death in the gland during the last week of gestation. We identified apoptotic cells in the regressing metrial gland by using DNA fragmentation, in situ DNA 3'-end labeling, and electron microscopy. Expression of progesterone receptor (PR) and estrogen receptor (ER) was also demonstrated by immunohistochemistry in the gland. The mean weight of metrial gland nodes decreased after day 18 of pregnancy. The apoptotic granulated metrial gland (GMG) cells that were detected by using the in situ DNA 3'-end labeling method were observed on day 16 of pregnancy, and they increased in number after day 20 of pregnancy. Intense fragmentation of DNA was also found from day 20 to day 22 of pregnancy. Electron microscopy demonstrated apoptotic GMG cells in the regressing metrial glands, confirming the results of the labeling studies. Immunohistochemical study revealed that expression of PR and ER, which were localized mainly in fibroblast-like stromal cells but not in GMG cells, was almost unchanged during late pregnancy. Apoptotic cell death is the major mode of rat metrial gland cell death in the peripartum loss of metrial gland cells.

Demonstration of extracellular acid phosphatase activity in the involuting, antimesometrial decidua in fed and acutely fasted mice by combined cytochemistry and electron microscopy

An ultrastructural cytochemical study of acid phosphatase activity in the antimesometrial decidua on days 9-11 of pregnancy was performed in fed and acutely fasted mice. Specimens were fixed in a buffered mixture of paraformaldehyde and glutaraldehyde and were incubated in a buffered medium containing sodium beta-glycerophosphate and cerium chloride for ultrastructural localization of acid phosphatase activity. Fed and fasted animals showed extracellular acid phosphatase reaction product in the decidual-trophoblast interface, in the region of loosely and tightly packed, mature decidual cells, and in the region of predecidual cells. Reaction product was absent in the region of nondecidualized stromal cells. Extracellular acid phosphatase activity was more conspicuous in the region of mature decidual cells in fasted mice than in fed mice, and it was apparently similar in the region of predecidual cells in both fed and fasted mice. Acid phosphatase reaction product was also observed in lysosomes in all cells studied. Because acid phosphatase activity reflects the presence of lysosomal hydrolases in general, our results suggest that there is matrix degradation by lysosomal enzymes in both fed and fasted mice. These events may be part of the process of tissue remodeling in regions of predecidual cells and mature decidual cells. However, it is also possible that, in the region of mature decidual cells, breakdown of matrix constituents is a mechanism to provide nutrients for the growing fetus. This mechanism is probably enhanced in fasted mice.

Developmental expression of extracellular glutathione peroxidase suggests antioxidant roles in deciduum, visceral yolk sac, and skin

Extracellular glutathione peroxidase (EGPx) is a secreted selenium-dependent enzyme that reduces hydroperoxides and organic hydroperoxides. Selenium deficiency in females is associated with infertility and spontaneous abortion, suggesting a role for selenium-requiring proteins during embryonic development. To gain insight into functions of EGPx in vivo, we determined sites of murine EGPx synthesis by in situ hybridization during embryogenesis and in adult tissues. At E7.5 of development, high EGPx expression was found in the maternally derived deciduum, with lower levels of accumulation in the embryonic visceral endoderm. At E9.5, the major sites of expression were the yolk sac endoderm and heart musculature. By E16.5, EGPx mRNA expression persisted in yolk sac endoderm but also accumulated significantly in atrially derived myocytes, ossification centers, adipose tissue, intestinal epithelium, and in a ventral-to-dorsal gradient in developing skin. Glutathione peroxidase activity due to EGPx protein was identified in the fluids surrounding the developing mouse embryo at midgestation. The expression of EGPx in tissues at the maternal-fetal interface--deciduum, visceral yolk sac, and skin--suggests that EGPx may serve to protect the embryo from oxidant damage. In adult mice, we identified the S1 segment of the kidney proximal tubules as the primary site of EGPx mRNA accumulation, with lower EGPx levels in atrial cardiac muscle, intestine, skin, and adipose tissue. These findings suggest that EGPx may serve a wider antioxidant role than previously recognized in the interstitium of multiple localized tissues, particularly those associated with the active transport of lipids.

Immunohistochemical analysis of beta 1-integrin receptors displayed by murine uterine natural killer cells over the course of successful pregnancy

Granulated metrial gland (GMG) cells are a natural killer (NK) cell-like population present in large numbers in the pregnant rodent uterus. By day 8 of gestation GMG cells are large and granulated and localized to the mesometrial side of each implantation site. GMG cells appear to be highly migratory both in vivo and in vitro; however, little is known regarding their functions. Using indirect fluorescence immunohistochemistry, murine uteri and implantation sites were studied on successive days of gestation to characterize the extracellular matrix receptors of the VLA-integrin family displayed by GMG cells. On days 3 and 6 of gestation, double immunostaining using the monoclonal antibody LGL-1 was employed to recognize GMG cells because their morphology early in pregnancy resembles that of other lymphocytes. Between days 8-15 of gestation, GMG cells can be recognized by their unique morphology. The day 3 and day 6 LGL-1+ cells were positive for all antigens examined; that is, beta 1 plus alpha 1, alpha 3, alpha 4, alpha 5 and alpha 6. From days 8-15 of gestation, GMG cells were beta 1+, alpha 4+, alpha 5+ but alpha 1-, alpha 3-, alpha 6-. Thus, between days 6-8 of gestation, major changes occur in the uterine NK/GMG cell population which include the loss of the surface molecules VLA alpha 1, alpha 3 and alpha 6 or the rapid expansion of NK cells not expressing these proteins. It is postulated that major changes in the functions of uterine NK cells are likely to be associated with these alterations in cell surface phenotype and that functional studies of uterine NK cells should focus upon this relatively early gestational time point.

Granulated metrial gland cells: hypotheses concerning possible functions during murine gestation

Granulated metrial gland (GMG) cells are morphologically distinctive lymphoid cells found in the murine uterus only during gestation. The life history of GMG cells suggests that they have important roles during mammalian gestation but these roles have been difficult to define. Genetic and immunologic data suggest that GMG cells may be a specialized subset of natural killer (NK) lymphocytes. This has directed research on GMG cell functions towards questions of effector cell-target cell interactions. A broader range of potential functions is discussed and shifts in functional roles played by GMG cells are proposed over the course of gestation.