MMP13 and adenomyosis: Moreover, the enzymes responsible for collagen degradation, MMP1, MMP8 and MMP13, and their natural inhibitor, tissue inhibitor of metallopeptidase 1 (TIMP1), also increased in the endometrium of women with adenomyosis (P = 0.002, P = 0.001, P = 0.008 and P = 0.0085, respectively), although changes in COL1A1, COL1A2 and COL3A1 mRNAs were not observed (FIGURE 3B and 3C).