Stromal cell interaction and relevance to predecidual events and menstruation.

Endometrial stromal cells play a vital role during decidualization and implantation. The aim of this study was to analyse the cyclic ultrastructural variations of stromal fibroblasts, granulocytes and blood-derived cells which invade the stroma during various stages of the menstrual cycle. Diverse opinions exist in the literature regarding the origin, fate and function of the endometrial granulocytes. Our study is in agreement with available immunological data and shows that (i) fibroblasts and granulocytes are distinct cell types in the stroma, (ii) they exhibit distinct changes across the menstrual cycle and (iii) fibroblasts are not the common progenitor for granulocytes and predecidual cells in the secretory phase endometrium, as suggested by previous investigators. The infiltration of eosinophils, platelets, macrophages, neutrophils, etc., during the menstrual phase makes the stroma a potential source of growth factors and cytokines which may regulate the process of regression and regeneration of the endometrium. Furthermore, we propose that endometrial granulocytes could be the source of decidual prolactin because the ultrastructural morphology of their secretory granules closely resembles that of the prolactin-secreting cells in the pituitary.