Endogenous activator of intestinal guanylate cyclase. It stimulates this enzyme through the same receptor binding region as the heat-stable enterotoxins. May be a potent physiological regulator of intestinal fluid and electrolyte transport. May be an autocrine/paracrine regulator of intestinal salt and water transport. Small and large intestine and atria and ventricles of heart. Both uroguanylin and prouroguanylin are found in plasma. Belongs to the guanylin family.