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. High expression in the brain localized to the pons/medulla with highest levels in pars ventromedialis of the dorsal tegmental nucleus. Significant expression is also detected in the spleen, thymus, lung, testis and ovary. Belongs to the insulin family.