Hormone that acts as a ligand for natriuretic peptide receptor NPR3/NPR-C and promotes bone growth and physical endurance in muscle. Acts as a regulator of osteoblast differentiation and bone growth by binding to natriuretic peptide receptor NPR3/NPR-C, thereby preventing binding between NPR3/NPR-C and natriuretic peptides, leading to increase cGMP production. Required to enhance physical endurance: induced following physical exercise in muscle and promotes cGMP production, probably by interacting with NPR3/NPR-C. May act as an autocrine and paracrine factor linked to glucose metabolism in skeletal muscle. Interacts with NPR3. Highly expressed in skeletal muscle (PubMed:15044443). Also expressed in leg tendons/ligaments and osteoblasts (PubMed:17951249). In long bones and teeth, present in knee joint and periodontal ligaments (at protein level) (PubMed:17951249). Expression was highest in embryos and neonates, peaking at 4 days of age in both calvaria and long bones and decreasing steadily with age to very low levels in 8-month-old long bones. The age-related decrease was less marked in calvaria by 8 months. Is down-regulated by 1,25-dihydroxy vitamin D3. Belongs to the Osteocrin family.