Summary
During pregnancy the increase in mass of the rat uterus has been accounted for mainly by hypertrophy rather than hyperplasia of the smooth muscle cells and by an increase in collagen content. Following parturition the rat uterus regains its non-pregnant weight within little more than a week. Autophagy is a likely mechanism for the reduction in size of the smooth muscle cells. However, many previous investigations have failed to demonstrate an extensive lysosomal apparatus in uterine smooth muscle cells, a morphologically detectable prerequisite for augmented autophagy. The superfluous collagen has been assumed to be digested by macrophages.
In the present electron microscopical study the involution of the rat uterus was followed at various time points post-partum. The results indicated that three pathways were involved namely, autophagocytosis, heterophagocytosis and crinophagy. Autophagocytosis was noted in smooth muscle cells — apparently a means to reduce their size. In some instances extensive autophagy appeared to lead to cell death. Macrophages and also to some extent fibroblasts have the ability to endocytose collagen and cell debris including split off portions of smooth muscle cell cytoplasm. The evidence obtained suggested that at the time of parturition the (pro)collagen synthesized but not yet secreted was retained within the fibroblasts and degraded by means of crinophagy.
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Henell, F., Ericsson, J.L.E. & Glaumann, H. An electron microscopic study of the post-partum involution of the rat uterus. Virchows Archiv B Cell Pathol 42, 271–287 (1983). https://doi.org/10.1007/BF02890390
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DOI: https://doi.org/10.1007/BF02890390