RESUMEN
In mammals, extensive remodeling of uterine endometrial matrix occurs during reproductive cycle and blastocyst implantation. This is regulated by a variety of molecules such as hormones, growth factors, cytokines and proteases. In this article, we review the current state of knowledge available on various proteases and their inhibitors functionally involved in the embryo-endometrial tissues and present some data on endometrial proteases in hamsters and rats during estrous cycle and early pregnancy. We demonstrate the presence of at least four gelatinolytic activities in endometrial samples, belonging to gelatinase-A and -B categories and their dependence on calcium/zinc ions for enzyme activity and, their interrelationships between zymogen and active forms. We believe that the embryo-endometrial proteases are essential for hatching of blastocysts and for the dynamic remodeling of endometrial tissues, occurring during the critical peri-implantation period.