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a hormone formed mainly in the ovaries that produces relaxation of the ligaments of the pubic symphysis of the pubic bones during pregnancy; as a result, the pelvis widens and normal childbirth is facilitated. Relaxin also characteristically inhibits the spontaneous contractions of the uterus.
Chemically relaxin is a polypeptide. Refined sow relaxin exhibits pronounced basic properties; it has molecular weight of about 6,500 and a structure of two subunits, consisting respectively of 22 and 28–31 amino-acid residues, joined by a disulfide bond. The primary structure has not been determined. The biosynthesis of either relaxin or the polypeptides that are closely related to it structurally is also possible in tissues found in the uterus and placenta.