Decidualisation: origin and role of associated cells.

Proliferation of peri- and subluminal stroma following a stimulus from the blastocyst leads to the appearance of decidual cells in the mammalian endometrium. Decidualisation can also be elicited by artificial stimuli in pseudopregnant animals. A variety of histophysiological reactions accompany decidualisation and distinct morphological features characterize decidual cells localized in the antimesometrial and mesometrial area. Granulated metrial gland cells, arising in the endometrium of decidualising uterus, form a separate class of cells and become prominent in the mesometrial triangle as pregnancy advances. This review deals with factors related to induction of decidualisation; structural characteristics of decidual and metrial gland cells; the origin and postulated roles of decidualisation-associated cells. The functional role of decidual and metrial gland cells is discussed in relation to their structural complexity and recent observations on the haemopoietic origin of these cells.