Regulation and restricted expression of interstitial collagenase suggest a pivotal role in the initiation of menstruation.

Collagenases are the only mammalian enzymes able to cleave, at neutral pH, the triple helical domain of fibrillar collagens, major constituents of the extracellular matrix of the endometrium. Interstitial collagenase is expressed, secreted and activated in human endometrium only just before and during menstruation. The expression of interstitial collagenase is restricted to the areas of the functional layer of the endometrium which are breaking down and to fragments which have been shed. In endometrial explants, combined sex steroids tightly control the expression, secretion and activation of interstitial collagenase, as well as the preservation of the extracellular matrix. These observations imply a pivotal role for this proteinase in the initiation of menstruation.