May play a role in neuropeptide signaling processes. Ligand for LGR7, relaxin-3 receptor-1 and relaxin-3 receptor-2 (By similarity). Heterodimer of a B chain and an A chain linked by two disulfide bonds. Highly abundant expression is detected in neurons within the ventomedial dorsal tegmental nucleus and the laterally central gray alpha of the pons. Also detected at much lower levels within the hippocampus. Belongs to the insulin family.