Seems to play a role in testicular function. May be a trophic hormone with a role in testicular descent in fetal life. Is a ligand for LGR8 receptor (By similarity). Heterodimer of a B chain and an A chain linked by two disulfide bonds. Expressed in Leydig cells of the testis, and weakly in the theca interna cells of antral follicles and the corpus luteum of the ovary. Highly expressed in adult testis and low expression in the ovary. Highly up-regulated in testes of day 19 embryos, but not in later neonatal stages, nor any ovarian tissue from this period. Belongs to the insulin family.