The permeability of the primary decidual zone in the rat uterus: an ultrastructural tracer and freeze-fracture study

Abstract

The rat primary decidual zone (PDZ) is a transitory avascular region of transformed fibroblasts surrounding the implanting embryo. Studies using fluorescein-labeled tracers have shown that the PDZ is selectively permeable to macromolecules, permeability decreasing with increasing molecular weight. In the present study we investigated the morphologic basis of the permeability barrier. Horseradish peroxidase (HRP) or HRP-labeled immunoglobulin G (IgG-HRP) was administered i.v. to rats on Day 7 of pregnancy, and the animals were killed 30 min to 2 h later. The reaction product of HRP was the same density in uterine blood vessels as in the intercellular spaces of the endometrium and PDZ at 30 min and 1 h after administration. Two hours after administration, the reaction product of IgG-HRP was dense in uterine blood vessels, much less dense in the interstitial spaces of the endometrium, and was not detected in the PDZ. There was an abrupt change in the density of the IgG-HRP reaction product at the intercellular clefts between endothelial cells, where cellular junctions were observed in control tissue. This suggests that the passage of large macromolecules from blood to the implantation chamber is limited initially by cellular junctions between capillary endothelial cells. The exclusion of IgG-HRP from the PDZ indicates that an additional barrier(s) to macromolecules in this region. Lanthanum nitrate tracer was uniformly present throughout the intercellular spaces of the PDZ except at tight junctions between decidual cells. Freeze-fracture replicas of the PDZ showed tight junctions that varied from single strands to interconnected networks of strands oriented mainly parallel to the long axis of the PDZ. Some strands were discontinuous. The tight junctions between decidual cells appear to be functionally discontinuous because HRP readily penetrated the PDZ, but such junctions may retard larger macromolecules such as IgG-HRP. The biological significance of the permeability barrier of the PDZ is discussed.

Embryonic signals direct the formation of tight junctional permeability barrier in the decidualizing stroma during embryo implantation

“…This is probably supportive of the formation of incomplete tight junctions in the PDZ Tung et al, 1986). Normal fertility in occludin-deficient mice suggests that it is not crucial during pregnancy (Saitou et al, 2000).…”

Immunolocalization of collagen type I and laminin in the uterus on days 5 to 8 of embryo implantation in the rat

“…This removal was evident on the evening of day 5 and raises the possibility that matrix changes may play an inductive role in regulating cellular phenotype (Bissell et al, 1982) and consequently in the process of decidualization (Aplin, 1989). Conversely, transformed cells have been associated with reduced expression of collagen (Kleinman et al, 1981) and thus 1986; Tung et al, 1986) protecting the embryo from the mother's immune response. If such a concept is correct the removal of the fibrillar collagen type I from throughout the decidua should allow closer cellular adhesion.…”

Localization of chondromodulin-I at the feto-maternal interface and its inhibitory actions on trophoblast invasion in vitro

“…Along with the invasion of trophoblasts into the maternal endometrium, sequential decidual reactions occur and lead to the formation of two distinct zones: the differentiated zone proximal to an implanting embryo termed the primary decidual zone, and the distal peripheral zone consisting of immature mitotic decidual cells, termed the secondary decidual zone [22,23]. In our present study, we have demonstrated that ChM-I is expressed in the primary decidual zone during early pregnancy in mice.…”