Relaxin is a peptide hormone produced by the corpora lutea of ovaries during pregnancy in many mammalian species, including man. The secretion of the hormone into the blood stream just before parturition results in a marked softening and lengthening of the pubic symphysis and a softening of the cervix, which facilitates the birth process. By inhibiting uterine contractions, relaxin may influence the timing of parturition. Like insulin, relaxin consists of two peptide chains, A and B, covalently linked by disulfide bonds. By further analogy to insulin, the two peptides are synthesized as a single-chain precursor polypeptide with the B chain at the NH2-terminus.