Relaxins are endocrine and autocrine/paracrine hormones belonging to the insulin gene superfamily. In several mammalian species, relaxin is best known for its role during pregnancy and parturition, when it is produced by the corpora lutea of ovaries and other reproductive tissues. The secretion of relaxin 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. Also, by inhibiting uterine contractions, relaxin may influence the timing of parturition. Two previously characterized orphan receptors designated relaxin receptor 1 (LGR7) and 2 (LGR8) bind relaxin in several tissues, including reproductive tissues, brain, and heart. Upon ligand binding, the relaxin receptors activate adenylate cyclases through Gs proteins. Expression of the relaxin receptors in tissues other than reproductive ones suggests that they have additional physiological functions, such as regulating blood pressure and controlling vascular volume in the heart.