Kallikreins and kinins in inflammatory-like events in the reproductive tract

The normal reproductive events of proliferation of the endometrial lining of the uterus during the menstrual cycle and ovulation have been likened to inflammatory-like events. The kallikrein-kinin system is involved in inflammatory processes in many tissues. In this review, we identify which components of the kallikrein-kinin system--the enzyme, tissue kallikrein; the substrate, low molecular weight kininogen and the effector receptor for the generated bradykinin peptide, the B2 receptor--have been identified in the uterus and ovary and their known involvement in the function of these organs. All three components have been localized to the glandular epithelial cells of the human endometrium. Tissue kallikrein gene expression is elevated midcycle when estrogens levels are also rising. This is also a time of extensive endometrial proliferation and tissue remodelling in preparation for embryo implantation, an event which is likened to other inflammatory processes. Similarly, tissue kallikrein gene expression was elevated following the estrogen surge at proestrous in the rat uterus, suggesting tissue kallikrein gene expression may be regulated by estrogens. Tissue kallikrein enzyme activity and gene expression has been demonstrated in the rat ovary and shown to be variously altered at the time of ovulation. Bradykinin has also been implicated in the expulsion of the ovum at the time of ovulation. These findings show that various components of the kallikrein-kinin system are present in the uterus and ovary. Further studies are required to more fully delineate their role in reproductive function.