Relaxin increases secretion of tissue inhibitor of matrix metalloproteinase-1 and -2 during uterine and cervical growth and remodeling in the pig.

Remodeling of reproductive organs during pregnancy requires degradation and resynthesis of structural barriers to cell invasion. Matrix metalloproteinases (MMPs) are enzymes that break down components of the extracellular matrix (ECM) and are essential for tissue remodeling processes. Tissue inhibitors of metalloproteinases (TIMPs) are important regulators of MMP activity. In the pig, relaxin stimulates growth and remodeling of the uterus and cervix during pregnancy, effects that include the ability to alter elements of the ECM. Therefore, the objective of this study was to determine whether relaxin alters the production and/or activity of TIMP-1 and TIMP-2 in the porcine uterus or cervix. The growth-promoting effects of relaxin were elicited by administering relaxin to prepubertal gilts every 6 h for 54 h. Expression of TIMP-1 and TIMP-2 was characterized by immunoblotting. Total enzyme activity was measured using an MMP-specific fluorescent substrate assay. TIMP-1 and TIMP-2 proteins were present in the uterus and cervix of control and relaxin-treated pigs, and both proteins were increased by relaxin in the uterine flushes and tissues (P < 0.05). Inhibitor activity in uterine tissue extracts and uterine flushes from relaxin-treated animals was greater than that in controls; however, this activity was restricted to inhibition of MMP-2. In the uterine cervix, relaxin enhanced expression of TIMP-1 and TIMP-2 (P < 0.05), whereas expression of both TIMP proteins was similar in the vaginal cervix of control and relaxin-treated animals. Likewise, inhibitor activity against MMP-2 in the uterine cervix was enhanced in response to relaxin (P < 0.05). In contrast, inhibitor activity was attenuated in extracts from the vaginal cervix (P < 0.05). This study highlights the complex nature of MMP/TIMP regulation during reproductive tissue growth and suggests that TIMP-1 and TIMP-2 may be involved in other aspects of the growth process. These data support a role for relaxin in regulating the activity of TIMPs during growth and remodeling of reproductive connective tissue.