Collagen degradation and mucosal mast cell in endometrium of mouse uterus during early postpartum period.

On the morning of the day of parturition, several parts in the endometrium showed edema in which collagen birefringence was not observed, indicating that collagen degradation occurs firstly in the endematous area. Undegradated collagen might be redistributed wholly in the endometrium on postpartum day 1 when the area of endometrium has diminished. The number of mucosal mast cells in the endometrium did not fluctuate in parallel with the endometrial collagen-degrading process, suggesting that mucosal mast cells do not participate in the collagen degradation during the early postpartum period.