Phagocytotic and iron-storing capacities of stromal cells in the rat endometrium. A histochemical and ultrastructural study

Cytoplasmic pigment inclusions of rat endometrial stromal cells were studied by histology, histochemistry, fluorescence microscopy, electron microscopy and X-ray microprobe analysis. It is shown that a number of endometrial perivascular stromal cells contain numerous free cytoplasmic ferritin particles as well as hemosiderin vacuoles. The larger pigment inclusions reveal also positive PAS- and Schmorl reactions indicating that they contain polysaccharide and lipofuscin material, respectively. These pigment-storing stromal cells also display acid phosphatase activity; they avidly phagocytose instillated latex particles. No pigment-storing cells occur within the surface or glandular epithelium, either in the basal endometrium or in the myometrium. It is demonstrated that the endometrial iron-storing cells function as iron depots; they take part in the phagocytosis and endocytosis of extracellular tissue components and therefore can be named phagocytes. Our data show that "fibroblastoid" endometrial stromal cells may differentiate into endometrial resident phagocytes, which ensure interstitial proteolysis and hence facilitate the drainage of extracellular fluid into the venous blood capillaries.