Cellular mechanisms involved in cyclic stromal renewal of the uterus. II. The albino rat

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Abstract
During the first four days postpartum, heterophils (polymorphonuclear leucocytes) and macrophages occur in the intercellular compartment of the luminal epithelium of the uterine endometrium. Cytochemical and ultrastructural evidence indicates that transepithelial emigration of these stromal cells to the uterine cavity is occurring. This event takes place while the luminal epithelium is proliferating in response to the estrogenic stimulus of the postpartum estrus.Heterophil emigration precedes that of the macrophages and is most conspicuous during days 1 and 2. Although it has been established that collagen fibrils occur in uterine phagocytes (Schwarz and Güldner, 1967) assumed to be macrophages (Parakkal, 1969, 1972), their precise role in collagen degradation remains undefined. It seems likely that the emigrating macrophages, heavily laden with phagolysosomal derivatives and lipid droplets, are hauling the remnants of the intercellular substance out of the endometrium during days 2–4 postpartum. Ultrastructural evidence indicates that the emigrating macrophage punctures the basal lamina and passes through the intercellular compartment of the luminal epithelium by active penetration.Another mode of macrophagic egress operates in the deep stroma of the endometrium and myometrium where lymphatic drainage occurs. Macrophages accumulate in the perilymphatic stroma as well as within lymphatic vessels.Thus macrophagic emigration through the luminal epithelium and lymphatic vessels may provide a cellular mechanism for elimination of the intercellular stromal substance in the regressing uterus. Transepithelial emigration is a mechanism which operates also in the marsupial uterus (Padykula and Taylor, 1976), and thus may be a fundamental mechanism among subprimate mammals that fulfills in part the function that menstruation effects in primates.