Uroguanylin and guanylin (GUCA2A; MIM 139392), peptide homologs of the bacterial heat-stable enterotoxins (e.g., the E. coli ST toxin; STa), are endogenous activators of the guanylate cyclase-2C receptor (GUCY2C; MIM 601330), which synthesizes cyclic GMP (cGMP), a key component of several intracellular signal transduction pathways.