Understanding Relaxin in the Female Reproductive System

Recent advances in our understanding of the hormone relaxin, and the discovery of its specific receptor LGR7, have provided a series of new tools and paradigms, with which to re-examine many aspects of female reproductive physiology classically associated with this hormone. It is important to distinguish those effects resulting from the endocrine actions of relaxin, due to secretion of the hormone, and possibly its precursor, from the corpus luteum of pregnancy, notably in rodents and other non-primate mammals, from the many local effects possibly involving paracrine interactions between receptors and locally synthesized hormone. Because in many tissues relaxin serves to upregulate the common second messenger cAMP, its effects are hard to unravel from other cAMP stimulants, with which there is inevitably some degree of redundancy. In this review, particularly the important role of relaxin in implantation is addressed, and also briefly the more established functions relating to uterine growth, cervical softening, placental development and rupture of the amniotic membranes.