Relaxin: new peptides, receptors and novel actions.

Relaxin has long been known as a hormone of pregnancy. Until recently, little was known of potential roles for relaxin in non-pregnant females and males. The identification of a new gene encoding relaxin-3 (RLN3), the discovery of the elusive relaxin receptor and a novel role for relaxin-1 in regulating the normal turnover of collagen has provided us with unique insights into potential new roles for this peptide family. The Rln3 gene appears to be predominantly expressed in the brain, and mapping studies indicate a highly developed network of Rln3, Rln1 and relaxin receptor-expressing cells in the brain, suggesting that relaxin peptides might have important roles in the central nervous system. Rln1-knockout mice show progressive tissue fibrosis as they age, and this fibrosis leads to functional changes in both the heart and lungs. Hence, the biological significance of this enigmatic peptide family is expanding, as are its potential clinical uses.