Removal of collagen bundles in murine uterus during postpartum involution

The localization of collagenolytic activity within the tissue compartments of the mouse uterus was investigated during postpartum involution. The rate of collagenase activity was measured by analysis of tissue levels of hydroxyproline from the day of parturition to the 10th postpartum day. Collagen bonding was analyzed by viewing birefringence induced by the picrosirius red-binding technique. An attempt was made to interrelate quantitative analysis with the histologic distribution of collagen during postpartum days 1-10. Histologic and quantitative evidence indicated the following: 1) The collagenous compartments of the endometrium and myometrium differ in their response to the postpartum rise in collagenase activity; collagen degradation occurs primarily in the endometrium, that is, the myometrial collagen remains, but much of the endometrial collagen is removed. 2) Endometrial collagen is degraded particularly in the immediate subluminal compartment.