Granulated metrial gland cells.

Granulated metrial gland (GMG) cells take their name from the metrial gland. The metrial gland is formed during pregnancy in many rodents with the appearance of GMG cells in the mesometrium at each implantation site. This paper reviews knowledge about GMG cells in rats and mice: the species most extensively studied. Granulated metrial gland cells are characterised by their cytoplasmic granules which contain glycoproteins and hydrolytic enzymes. The cytoplasm of some GMG cells contains extensive deposits of glycogen and moderate amounts of rough endoplasmic reticulum and Golgi bodies are usually present. Some GMG cells are binucleate and at certain stages of pregnancy many undergo mitosis. A few GMG cells are present in the endometrium (in mice) before implantation but in rats and mice during the week following implantation their numbers rapidly increase. During the 2nd week of gestation GMG cells are a prominent cell population in the decidua basalis and they appear in the circular layer of the myometrium and within the mesometrial triangle. By the beginning of the 3rd week of gestation they are present in the metrial gland in large numbers but they disappear and are relatively scarce at parturition. Rat and mouse GMG cells are readily distinguished by differences in the ultrastructure of their electron-dense granules. These differences have made it possible to show that GMG cells differentiate from bone marrow cell precursors by studying GMG cells in radiation-induced chimeric mice. The disappearance of GMG cells from the decidua basalis and metrial gland as pregnancy proceeds is accounted for by their death in situ and by their migration into blood vessels. Some GMG cells probably become trapped in lung capillary beds but the GMG cells in the maternal blood spaces of the placental labyrinth appear to interact with some layer 1 trophoblast cells and degeneration of the trophoblast and GMG cells occurs. Other cell types present in the uterus are described and their relationships to GMG cells considered. A close morphological relationship exists between cells in the decidua basalis and GMG cells and between fibroblast-like stromal cells in the metrial gland and GMG cells. Although initially GMG cells are closely packed between smooth muscle cells at the base of the mesometrium, the organisation of muscle cells in this region is disrupted with the formation of the metrial gland. Macrophages are considered, particularly in relationship to endocytotic activity of cells in the uterus, and it is argued that "it is not appropriate simply to dismiss GMG cells as macrophages".(ABSTRACT TRUNCATED AT 400 WORDS)