Actions of Relaxin on Non-Reproductive Tissues

Initially thought of as primarily a reproductive hormone, relaxin is emerging as a multi-functional factor in a broad range of target tissues including the cardiovascular, renal, and respiratory systems, in addition to the brain, skin, liver and other less studied organs. The ever-increasing detection of H2/relaxin and the newly discovered H3/relaxin-3 gene transcripts and/or immunostaining in several non-reproductive organs suggests that these tissues may act as nonovarian sources of relaxin production in numerous mammalian species. Furthermore, the recent discovery that the relaxin receptor was identified as an orphan leucine-rich repeat containing G-protein coupled receptor-7 (LGR7), and subsequent detection of LGR7 expression in several non-reproductive tissues have confirmed these organs as targets for relaxin binding and activity. This review, discusses evidence from several studies that collectively demonstrate the many diverse and vital roles that relaxin plays in male and non-pregnant female mammals, each with significant therapeutic and clinical implications. Relaxin has been reported to decrease extracellular matrix turnover, when stimulated by chemical, surgical and genetic means, in addition to organ scarring (fibrosis) in the heart, lung, kidney, liver and skin. Relaxin also protects many non-reproductive organs through its ability to promote vasodilation of the vasculature, angiogenesis and wound healing, while counteracting allergic reactions via its anti-inflammatory actions. Furthermore, the identification of relaxin peptides and receptors in numerous regions of the brain, involved in a range of sensory and autonomic functions has expanded the biological significance of the relaxin peptide family. Keywords: relaxin, cardiovascular system, kidney, lung, brain, skin, liver, connective tissue, fibrosis, inflammation