Structurally, relaxin is a heterodimer of two peptide chains of 24 and 29 amino acids that are linked by disulfide bridges and it appears related to insulin.
Relaxin is produced from its prohormone, “pro-relaxin”, by splitting off one additional peptide chain.
The function of relaxin in humans is not clear, although it has several functions in animals.
In women relaxin levels rise after ovulation as a result of its production by the corpus luteum. In the absence of pregnancy its level declines at menstruation. During the first trimester of pregnancy levels rise and additional relaxin is produced by the decidua.
Relaxin's role or necessity in human pregnancy remains under investigation, as in humans its peak is reached during the first trimester, not toward the end of pregnancy.
In animals relaxin widens the pubic bone and facilitates labor, it also softens the cervix (cervical ripening), and relaxes the uterine musculature. Thus, for a long time, relaxin was looked at as a pregnancy hormone. However, its significance may reach much further. Relaxin affects collagen metabolism, inhibiting collagen synthesis and enhancing its breakdown by increasing matrix metalloproteinases. It also enhances angiogenesis and is a potent renal vasodilator.
Relaxin interacts with the relaxin receptor LGR7 (RXFP1) and LGR8 (RXFP2) which belong to the G-protein-coupled receptor superfamily. They contain a heptahelical transmembrane domain and a large glycosylated ectodomain, distantly related to the receptors for the glycoproteohormones, such as the LH-receptor or FSH-receptor.
^ Becker G, Hewitson T (2001). "Relaxin and renal fibrosis". Kidney Int59 (3): 1184-5. PMID 11231378.
^ Mookerjee I, Solly N, Royce S, Tregear G, Samuel C, Tang M (2006). "Endogenous relaxin regulates collagen deposition in an animal model of allergic airway disease". Endocrinology147 (2): 754-61. PMID 16254028.
^ Van Der Westhuizen E, Summers R, Halls M, Bathgate R, Sexton P (2007). "Relaxin receptors--new drug targets for multiple disease states". Curr Drug Targets8 (1): 91-104. PMID 17266534.